[project @ 2001-03-23 16:36:20 by simonmar]
[ghc-hetmet.git] / ghc / rts / Schedule.c
index afd73f8..5451cc5 100644 (file)
@@ -1,11 +1,78 @@
-/* -----------------------------------------------------------------------------
- * $Id: Schedule.c,v 1.21 1999/05/11 16:47:57 keithw Exp $
+/* ---------------------------------------------------------------------------
+ * $Id: Schedule.c,v 1.95 2001/03/23 16:36:21 simonmar Exp $
  *
  *
- * (c) The GHC Team, 1998-1999
+ * (c) The GHC Team, 1998-2000
  *
  * Scheduler
  *
  *
  * Scheduler
  *
- * ---------------------------------------------------------------------------*/
+ * Different GHC ways use this scheduler quite differently (see comments below)
+ * Here is the global picture:
+ *
+ * WAY  Name     CPP flag  What's it for
+ * --------------------------------------
+ * mp   GUM      PAR       Parallel execution on a distributed memory machine
+ * s    SMP      SMP       Parallel execution on a shared memory machine
+ * mg   GranSim  GRAN      Simulation of parallel execution
+ * md   GUM/GdH  DIST      Distributed execution (based on GUM)
+ * --------------------------------------------------------------------------*/
+
+//@node Main scheduling code, , ,
+//@section Main scheduling code
+
+/* 
+ * Version with scheduler monitor support for SMPs (WAY=s):
+
+   This design provides a high-level API to create and schedule threads etc.
+   as documented in the SMP design document.
+
+   It uses a monitor design controlled by a single mutex to exercise control
+   over accesses to shared data structures, and builds on the Posix threads
+   library.
+
+   The majority of state is shared.  In order to keep essential per-task state,
+   there is a Capability structure, which contains all the information
+   needed to run a thread: its STG registers, a pointer to its TSO, a
+   nursery etc.  During STG execution, a pointer to the capability is
+   kept in a register (BaseReg).
+
+   In a non-SMP build, there is one global capability, namely MainRegTable.
+
+   SDM & KH, 10/99
+
+ * Version with support for distributed memory parallelism aka GUM (WAY=mp):
+
+   The main scheduling loop in GUM iterates until a finish message is received.
+   In that case a global flag @receivedFinish@ is set and this instance of
+   the RTS shuts down. See ghc/rts/parallel/HLComms.c:processMessages()
+   for the handling of incoming messages, such as PP_FINISH.
+   Note that in the parallel case we have a system manager that coordinates
+   different PEs, each of which are running one instance of the RTS.
+   See ghc/rts/parallel/SysMan.c for the main routine of the parallel program.
+   From this routine processes executing ghc/rts/Main.c are spawned. -- HWL
+
+ * Version with support for simulating parallel execution aka GranSim (WAY=mg):
+
+   The main scheduling code in GranSim is quite different from that in std
+   (concurrent) Haskell: while concurrent Haskell just iterates over the
+   threads in the runnable queue, GranSim is event driven, i.e. it iterates
+   over the events in the global event queue.  -- HWL
+*/
+
+//@menu
+//* Includes::                 
+//* Variables and Data structures::  
+//* Main scheduling loop::     
+//* Suspend and Resume::       
+//* Run queue code::           
+//* Garbage Collextion Routines::  
+//* Blocking Queue Routines::  
+//* Exception Handling Routines::  
+//* Debugging Routines::       
+//* Index::                    
+//@end menu
+
+//@node Includes, Variables and Data structures, Main scheduling code, Main scheduling code
+//@subsection Includes
 
 #include "Rts.h"
 #include "SchedAPI.h"
 
 #include "Rts.h"
 #include "SchedAPI.h"
 #include "Schedule.h"
 #include "StgMiscClosures.h"
 #include "Storage.h"
 #include "Schedule.h"
 #include "StgMiscClosures.h"
 #include "Storage.h"
-#include "Evaluator.h"
+#include "Interpreter.h"
+#include "Exception.h"
 #include "Printer.h"
 #include "Main.h"
 #include "Signals.h"
 #include "Printer.h"
 #include "Main.h"
 #include "Signals.h"
-#include "Profiling.h"
 #include "Sanity.h"
 #include "Sanity.h"
+#include "Stats.h"
+#include "Itimer.h"
+#include "Prelude.h"
+#if defined(GRAN) || defined(PAR)
+# include "GranSimRts.h"
+# include "GranSim.h"
+# include "ParallelRts.h"
+# include "Parallel.h"
+# include "ParallelDebug.h"
+# include "FetchMe.h"
+# include "HLC.h"
+#endif
+#include "Sparks.h"
+
+#include <stdarg.h>
+
+//@node Variables and Data structures, Prototypes, Includes, Main scheduling code
+//@subsection Variables and Data structures
+
+/* Main threads:
+ *
+ * These are the threads which clients have requested that we run.  
+ *
+ * In an SMP build, we might have several concurrent clients all
+ * waiting for results, and each one will wait on a condition variable
+ * until the result is available.
+ *
+ * In non-SMP, clients are strictly nested: the first client calls
+ * into the RTS, which might call out again to C with a _ccall_GC, and
+ * eventually re-enter the RTS.
+ *
+ * Main threads information is kept in a linked list:
+ */
+//@cindex StgMainThread
+typedef struct StgMainThread_ {
+  StgTSO *         tso;
+  SchedulerStatus  stat;
+  StgClosure **    ret;
+#ifdef SMP
+  pthread_cond_t wakeup;
+#endif
+  struct StgMainThread_ *link;
+} StgMainThread;
+
+/* Main thread queue.
+ * Locks required: sched_mutex.
+ */
+static StgMainThread *main_threads;
+
+/* Thread queues.
+ * Locks required: sched_mutex.
+ */
+#if defined(GRAN)
+
+StgTSO* ActiveTSO = NULL; /* for assigning system costs; GranSim-Light only */
+/* rtsTime TimeOfNextEvent, EndOfTimeSlice;            now in GranSim.c */
+
+/* 
+   In GranSim we have a runable and a blocked queue for each processor.
+   In order to minimise code changes new arrays run_queue_hds/tls
+   are created. run_queue_hd is then a short cut (macro) for
+   run_queue_hds[CurrentProc] (see GranSim.h).
+   -- HWL
+*/
+StgTSO *run_queue_hds[MAX_PROC], *run_queue_tls[MAX_PROC];
+StgTSO *blocked_queue_hds[MAX_PROC], *blocked_queue_tls[MAX_PROC];
+StgTSO *ccalling_threadss[MAX_PROC];
+/* We use the same global list of threads (all_threads) in GranSim as in
+   the std RTS (i.e. we are cheating). However, we don't use this list in
+   the GranSim specific code at the moment (so we are only potentially
+   cheating).  */
+
+#else /* !GRAN */
 
 StgTSO *run_queue_hd, *run_queue_tl;
 StgTSO *blocked_queue_hd, *blocked_queue_tl;
 
 StgTSO *run_queue_hd, *run_queue_tl;
 StgTSO *blocked_queue_hd, *blocked_queue_tl;
-StgTSO *ccalling_threads;
+StgTSO *sleeping_queue;                /* perhaps replace with a hash table? */
 
 
-#define MAX_SCHEDULE_NESTING 256
-nat next_main_thread;
-StgTSO *main_threads[MAX_SCHEDULE_NESTING];
+#endif
+
+/* Linked list of all threads.
+ * Used for detecting garbage collected threads.
+ */
+StgTSO *all_threads;
+
+/* Threads suspended in _ccall_GC.
+ */
+static StgTSO *suspended_ccalling_threads;
 
 static void GetRoots(void);
 static StgTSO *threadStackOverflow(StgTSO *tso);
 
 
 static void GetRoots(void);
 static StgTSO *threadStackOverflow(StgTSO *tso);
 
+/* KH: The following two flags are shared memory locations.  There is no need
+       to lock them, since they are only unset at the end of a scheduler
+       operation.
+*/
+
 /* flag set by signal handler to precipitate a context switch */
 /* flag set by signal handler to precipitate a context switch */
+//@cindex context_switch
 nat context_switch;
 nat context_switch;
+
 /* if this flag is set as well, give up execution */
 /* if this flag is set as well, give up execution */
-static nat interrupted;
+//@cindex interrupted
+rtsBool interrupted;
 
 
-/* Next thread ID to allocate */
+/* Next thread ID to allocate.
+ * Locks required: sched_mutex
+ */
+//@cindex next_thread_id
 StgThreadID next_thread_id = 1;
 
 /*
 StgThreadID next_thread_id = 1;
 
 /*
@@ -50,14 +208,7 @@ StgThreadID next_thread_id = 1;
  * Rule of thumb: if CurrentTSO != NULL, then we're running a Haskell
  * thread.  If CurrentTSO == NULL, then we're at the scheduler level.
  */
  * Rule of thumb: if CurrentTSO != NULL, then we're running a Haskell
  * thread.  If CurrentTSO == NULL, then we're at the scheduler level.
  */
-StgTSO      *CurrentTSO;
-StgRegTable  MainRegTable;
-
-/*
- * The thread state for the main thread.
- */
-StgTSO   *MainTSO;
-
 /* The smallest stack size that makes any sense is:
  *    RESERVED_STACK_WORDS    (so we can get back from the stack overflow)
  *  + sizeofW(StgStopFrame)   (the stg_stop_thread_info frame)
 /* The smallest stack size that makes any sense is:
  *    RESERVED_STACK_WORDS    (so we can get back from the stack overflow)
  *  + sizeofW(StgStopFrame)   (the stg_stop_thread_info frame)
@@ -70,399 +221,1929 @@ StgTSO   *MainTSO;
 
 #define MIN_STACK_WORDS (RESERVED_STACK_WORDS + sizeofW(StgStopFrame) + 2)
 
 
 #define MIN_STACK_WORDS (RESERVED_STACK_WORDS + sizeofW(StgStopFrame) + 2)
 
-/* -----------------------------------------------------------------------------
- * Static functions
- * -------------------------------------------------------------------------- */
-static void unblockThread(StgTSO *tso);
-
-/* -----------------------------------------------------------------------------
-   Create a new thread.
-
-   The new thread starts with the given stack size.  Before the
-   scheduler can run, however, this thread needs to have a closure
-   (and possibly some arguments) pushed on its stack.  See
-   pushClosure() in Schedule.h.
-
-   createGenThread() and createIOThread() (in SchedAPI.h) are
-   convenient packaged versions of this function.
-   -------------------------------------------------------------------------- */
+/* Free capability list.
+ * Locks required: sched_mutex.
+ */
+#ifdef SMP
+//@cindex free_capabilities
+//@cindex n_free_capabilities
+Capability *free_capabilities; /* Available capabilities for running threads */
+nat n_free_capabilities;       /* total number of available capabilities */
+#else
+//@cindex MainRegTable
+Capability MainRegTable;       /* for non-SMP, we have one global capability */
+#endif
 
 
-StgTSO *
-createThread(nat stack_size)
-{
-  StgTSO *tso;
+#if defined(GRAN)
+StgTSO *CurrentTSO;
+#endif
 
 
-  /* catch ridiculously small stack sizes */
-  if (stack_size < MIN_STACK_WORDS + TSO_STRUCT_SIZEW) {
-    stack_size = MIN_STACK_WORDS + TSO_STRUCT_SIZEW;
-  }
+/*  This is used in `TSO.h' and gcc 2.96 insists that this variable actually 
+ *  exists - earlier gccs apparently didn't.
+ *  -= chak
+ */
+StgTSO dummy_tso;
 
 
-  tso = (StgTSO *)allocate(stack_size);
-  TICK_ALLOC_TSO(stack_size-sizeofW(StgTSO),0);
-  
-  initThread(tso, stack_size - TSO_STRUCT_SIZEW);
-  return tso;
-}
+rtsBool ready_to_gc;
 
 
-void
-initThread(StgTSO *tso, nat stack_size)
-{
-  SET_INFO(tso,&TSO_info);
-  tso->whatNext     = ThreadEnterGHC;
-  tso->id           = next_thread_id++;
-  tso->blocked_on   = NULL;
+/* All our current task ids, saved in case we need to kill them later.
+ */
+#ifdef SMP
+//@cindex task_ids
+task_info *task_ids;
+#endif
 
 
-  tso->splim        = (P_)&(tso->stack) + RESERVED_STACK_WORDS;
-  tso->stack_size   = stack_size;
-  tso->max_stack_size = round_to_mblocks(RtsFlags.GcFlags.maxStkSize) 
-                              - TSO_STRUCT_SIZEW;
-  tso->sp           = (P_)&(tso->stack) + stack_size;
+void            addToBlockedQueue ( StgTSO *tso );
 
 
-#ifdef PROFILING
-  tso->prof.CCCS = CCS_MAIN;
+static void     schedule          ( void );
+       void     interruptStgRts   ( void );
+#if defined(GRAN)
+static StgTSO * createThread_     ( nat size, rtsBool have_lock, StgInt pri );
+#else
+static StgTSO * createThread_     ( nat size, rtsBool have_lock );
 #endif
 
 #endif
 
-  /* put a stop frame on the stack */
-  tso->sp -= sizeofW(StgStopFrame);
-  SET_HDR((StgClosure*)tso->sp,(StgInfoTable *)&stg_stop_thread_info,CCS_MAIN);
-  tso->su = (StgUpdateFrame*)tso->sp;
+static void     detectBlackHoles  ( void );
 
 
-  IF_DEBUG(scheduler,belch("Initialised thread %ld, stack size = %lx words\n", 
-                          tso->id, tso->stack_size));
+#ifdef DEBUG
+static void sched_belch(char *s, ...);
+#endif
 
 
-  /* Put the new thread on the head of the runnable queue.
-   * The caller of createThread better push an appropriate closure
-   * on this thread's stack before the scheduler is invoked.
-   */
-  tso->link = run_queue_hd;
-  run_queue_hd = tso;
-  if (run_queue_tl == END_TSO_QUEUE) {
-    run_queue_tl = tso;
-  }
+#ifdef SMP
+//@cindex sched_mutex
+//@cindex term_mutex
+//@cindex thread_ready_cond
+//@cindex gc_pending_cond
+pthread_mutex_t sched_mutex       = PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t term_mutex        = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t  thread_ready_cond = PTHREAD_COND_INITIALIZER;
+pthread_cond_t  gc_pending_cond   = PTHREAD_COND_INITIALIZER;
+
+nat await_death;
+#endif
 
 
-  IF_DEBUG(scheduler,printTSO(tso));
-}
+#if defined(PAR)
+StgTSO *LastTSO;
+rtsTime TimeOfLastYield;
+rtsBool emitSchedule = rtsTrue;
+#endif
 
 
-/* -----------------------------------------------------------------------------
- * initScheduler()
- *
- * Initialise the scheduler.  This resets all the queues - if the
- * queues contained any threads, they'll be garbage collected at the
- * next pass.
- * -------------------------------------------------------------------------- */
+#if DEBUG
+char *whatNext_strs[] = {
+  "ThreadEnterGHC",
+  "ThreadRunGHC",
+  "ThreadEnterInterp",
+  "ThreadKilled",
+  "ThreadComplete"
+};
+
+char *threadReturnCode_strs[] = {
+  "HeapOverflow",                      /* might also be StackOverflow */
+  "StackOverflow",
+  "ThreadYielding",
+  "ThreadBlocked",
+  "ThreadFinished"
+};
+#endif
 
 
-void initScheduler(void)
-{
-  run_queue_hd      = END_TSO_QUEUE;
-  run_queue_tl      = END_TSO_QUEUE;
-  blocked_queue_hd  = END_TSO_QUEUE;
-  blocked_queue_tl  = END_TSO_QUEUE;
-  ccalling_threads  = END_TSO_QUEUE;
-  next_main_thread  = 0;
+#ifdef PAR
+StgTSO * createSparkThread(rtsSpark spark);
+StgTSO * activateSpark (rtsSpark spark);  
+#endif
 
 
-  context_switch = 0;
-  interrupted    = 0;
+/*
+ * The thread state for the main thread.
+// ToDo: check whether not needed any more
+StgTSO   *MainTSO;
+ */
 
 
-  enteredCAFs = END_CAF_LIST;
-}
+//@node Main scheduling loop, Suspend and Resume, Prototypes, Main scheduling code
+//@subsection Main scheduling loop
 
 
-/* -----------------------------------------------------------------------------
+/* ---------------------------------------------------------------------------
    Main scheduling loop.
 
    We use round-robin scheduling, each thread returning to the
    scheduler loop when one of these conditions is detected:
 
    Main scheduling loop.
 
    We use round-robin scheduling, each thread returning to the
    scheduler loop when one of these conditions is detected:
 
-      * stack overflow
       * out of heap space
       * timer expires (thread yields)
       * thread blocks
       * thread ends
       * out of heap space
       * timer expires (thread yields)
       * thread blocks
       * thread ends
-   -------------------------------------------------------------------------- */
+      * stack overflow
 
 
-SchedulerStatus schedule(StgTSO *main, StgClosure **ret_val)
+   Locking notes:  we acquire the scheduler lock once at the beginning
+   of the scheduler loop, and release it when
+    
+      * running a thread, or
+      * waiting for work, or
+      * waiting for a GC to complete.
+
+   GRAN version:
+     In a GranSim setup this loop iterates over the global event queue.
+     This revolves around the global event queue, which determines what 
+     to do next. Therefore, it's more complicated than either the 
+     concurrent or the parallel (GUM) setup.
+
+   GUM version:
+     GUM iterates over incoming messages.
+     It starts with nothing to do (thus CurrentTSO == END_TSO_QUEUE),
+     and sends out a fish whenever it has nothing to do; in-between
+     doing the actual reductions (shared code below) it processes the
+     incoming messages and deals with delayed operations 
+     (see PendingFetches).
+     This is not the ugliest code you could imagine, but it's bloody close.
+
+   ------------------------------------------------------------------------ */
+//@cindex schedule
+static void
+schedule( void )
 {
   StgTSO *t;
 {
   StgTSO *t;
+  Capability *cap;
   StgThreadReturnCode ret;
   StgThreadReturnCode ret;
-  StgTSO **MainTSO;
-  rtsBool in_ccall_gc;
+#if defined(GRAN)
+  rtsEvent *event;
+#elif defined(PAR)
+  StgSparkPool *pool;
+  rtsSpark spark;
+  StgTSO *tso;
+  GlobalTaskId pe;
+  rtsBool receivedFinish = rtsFalse;
+# if defined(DEBUG)
+  nat tp_size, sp_size; // stats only
+# endif
+#endif
+  rtsBool was_interrupted = rtsFalse;
+  
+  ACQUIRE_LOCK(&sched_mutex);
 
 
-  /* Return value is NULL by default, it is only filled in if the
-   * main thread completes successfully.
-   */
-  if (ret_val) { *ret_val = NULL; }
+#if defined(GRAN)
 
 
-  /* Save away a pointer to the main thread so that we can keep track
-   * of it should a garbage collection happen.  We keep a stack of
-   * main threads in order to support scheduler re-entry.  We can't
-   * use the normal TSO linkage for this stack, because the main TSO
-   * may need to be linked onto other queues.
-   */
-  main_threads[next_main_thread] = main;
-  MainTSO = &main_threads[next_main_thread];
-  next_main_thread++;
-  IF_DEBUG(scheduler,
-          fprintf(stderr, "Scheduler entered: nesting = %d\n", 
-                  next_main_thread););
+  /* set up first event to get things going */
+  /* ToDo: assign costs for system setup and init MainTSO ! */
+  new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
+           ContinueThread, 
+           CurrentTSO, (StgClosure*)NULL, (rtsSpark*)NULL);
 
 
-  /* Are we being re-entered? 
-   */
-  if (CurrentTSO != NULL) {
-    /* This happens when a _ccall_gc from Haskell ends up re-entering
-     * the scheduler.
-     *
-     * Block the current thread (put it on the ccalling_queue) and
-     * continue executing.  The calling thread better have stashed
-     * away its state properly and left its stack with a proper stack
-     * frame on the top.
-     */
-    threadPaused(CurrentTSO);
-    CurrentTSO->link = ccalling_threads;
-    ccalling_threads = CurrentTSO;
-    in_ccall_gc = rtsTrue;
-    IF_DEBUG(scheduler,
-            fprintf(stderr, "Re-entry, thread %d did a _ccall_gc\n", 
-                    CurrentTSO->id););
-  } else {
-    in_ccall_gc = rtsFalse;
-  }
+  IF_DEBUG(gran,
+          fprintf(stderr, "GRAN: Init CurrentTSO (in schedule) = %p\n", CurrentTSO);
+          G_TSO(CurrentTSO, 5));
 
 
-  /* Take a thread from the run queue.
-   */
-  t = run_queue_hd;
-  if (t != END_TSO_QUEUE) {
-    run_queue_hd = t->link;
-    t->link = END_TSO_QUEUE;
-    if (run_queue_hd == END_TSO_QUEUE) {
-      run_queue_tl = END_TSO_QUEUE;
-    }
-  }
+  if (RtsFlags.GranFlags.Light) {
+    /* Save current time; GranSim Light only */
+    CurrentTSO->gran.clock = CurrentTime[CurrentProc];
+  }      
 
 
-  while (t != END_TSO_QUEUE) {
-    CurrentTSO = t;
+  event = get_next_event();
 
 
-    /* If we have more threads on the run queue, set up a context
-     * switch at some point in the future.
-     */
-    if (run_queue_hd != END_TSO_QUEUE) {
-      context_switch = 1;
-    } else {
-      context_switch = 0;
-    }
-    IF_DEBUG(scheduler, belch("Running thread %ld...\n", t->id));
+  while (event!=(rtsEvent*)NULL) {
+    /* Choose the processor with the next event */
+    CurrentProc = event->proc;
+    CurrentTSO = event->tso;
 
 
-    /* Be friendly to the storage manager: we're about to *run* this
-     * thread, so we better make sure the TSO is mutable.
-     */
-    if (t->mut_link == NULL) {
-      recordMutable((StgMutClosure *)t);
-    }
+#elif defined(PAR)
 
 
-    /* Run the current thread */
-    switch (t->whatNext) {
-    case ThreadKilled:
-    case ThreadComplete:
-      /* thread already killed.  Drop it and carry on. */
-      goto next_thread;
-    case ThreadEnterGHC:
-      ret = StgRun((StgFunPtr) stg_enterStackTop);
-      break;
-    case ThreadRunGHC:
-      ret = StgRun((StgFunPtr) stg_returnToStackTop);
-      break;
-    case ThreadEnterHugs:
-#ifdef INTERPRETER
-      {  
-         IF_DEBUG(scheduler,belch("entering Hugs"));     
-         LoadThreadState();
-         /* CHECK_SENSIBLE_REGS(); */
-         {
-             StgClosure* c = (StgClosure *)Sp[0];
-             Sp += 1;
-             ret = enter(c);
-         }     
-         SaveThreadState();
-         break;
-      }
+  while (!receivedFinish) {    /* set by processMessages */
+                               /* when receiving PP_FINISH message         */ 
 #else
 #else
-      barf("Panic: entered a BCO but no bytecode interpreter in this build");
-#endif
-    default:
-      barf("schedule: invalid whatNext field");
-    }
 
 
-    /* We may have garbage collected while running the thread
-     * (eg. something nefarious like _ccall_GC_ performGC), and hence
-     * CurrentTSO may have moved.  Update t to reflect this.
-     */
-    t = CurrentTSO;
-    CurrentTSO = NULL;
+  while (1) {
 
 
-    /* Costs for the scheduler are assigned to CCS_SYSTEM */
-#ifdef PROFILING
-    CCCS = CCS_SYSTEM;
 #endif
 
 #endif
 
-    switch (ret) {
+    IF_DEBUG(scheduler, printAllThreads());
 
 
-    case HeapOverflow:
-      IF_DEBUG(scheduler,belch("Thread %ld stopped: HeapOverflow\n", t->id));
-      threadPaused(t);
-      PUSH_ON_RUN_QUEUE(t);
-      GarbageCollect(GetRoots);
-      break;
+    /* If we're interrupted (the user pressed ^C, or some other
+     * termination condition occurred), kill all the currently running
+     * threads.
+     */
+    if (interrupted) {
+      IF_DEBUG(scheduler, sched_belch("interrupted"));
+      deleteAllThreads();
+      interrupted = rtsFalse;
+      was_interrupted = rtsTrue;
+    }
 
 
-    case StackOverflow:
-      IF_DEBUG(scheduler,belch("Thread %ld stopped, StackOverflow\n", t->id));
-      { 
-       nat i;
-       /* enlarge the stack */
-       StgTSO *new_t = threadStackOverflow(t);
-       
-       /* This TSO has moved, so update any pointers to it from the
-        * main thread stack.  It better not be on any other queues...
-        * (it shouldn't be)
-        */
-       for (i = 0; i < next_main_thread; i++) {
-         if (main_threads[i] == t) {
-           main_threads[i] = new_t;
+    /* Go through the list of main threads and wake up any
+     * clients whose computations have finished.  ToDo: this
+     * should be done more efficiently without a linear scan
+     * of the main threads list, somehow...
+     */
+#ifdef SMP
+    { 
+      StgMainThread *m, **prev;
+      prev = &main_threads;
+      for (m = main_threads; m != NULL; m = m->link) {
+       switch (m->tso->what_next) {
+       case ThreadComplete:
+         if (m->ret) {
+           *(m->ret) = (StgClosure *)m->tso->sp[0];
+         }
+         *prev = m->link;
+         m->stat = Success;
+         pthread_cond_broadcast(&m->wakeup);
+         break;
+       case ThreadKilled:
+         *prev = m->link;
+         if (was_interrupted) {
+           m->stat = Interrupted;
+         } else {
+           m->stat = Killed;
          }
          }
+         pthread_cond_broadcast(&m->wakeup);
+         break;
+       default:
+         break;
        }
        }
-       t = new_t;
       }
       }
-      PUSH_ON_RUN_QUEUE(t);
-      break;
+    }
 
 
-    case ThreadYielding:
-      IF_DEBUG(scheduler,
-               if (t->whatNext == ThreadEnterHugs) {
-                  /* ToDo: or maybe a timer expired when we were in Hugs?
-                   * or maybe someone hit ctrl-C
-                    */
-                   belch("Thread %ld stopped to switch to Hugs\n", t->id);
-               } else {
-                   belch("Thread %ld stopped, timer expired\n", t->id);
-               }
-               );
-      threadPaused(t);
-      if (interrupted) {
-          IF_DEBUG(scheduler,belch("Scheduler interrupted - returning"));
-         deleteThread(t);
-         while (run_queue_hd != END_TSO_QUEUE) {
-             run_queue_hd = t->link;
-             deleteThread(t);
+#else
+# if defined(PAR)
+    /* in GUM do this only on the Main PE */
+    if (IAmMainThread)
+# endif
+    /* If our main thread has finished or been killed, return.
+     */
+    {
+      StgMainThread *m = main_threads;
+      if (m->tso->what_next == ThreadComplete
+         || m->tso->what_next == ThreadKilled) {
+       main_threads = main_threads->link;
+       if (m->tso->what_next == ThreadComplete) {
+         /* we finished successfully, fill in the return value */
+         if (m->ret) { *(m->ret) = (StgClosure *)m->tso->sp[0]; };
+         m->stat = Success;
+         return;
+       } else {
+         if (was_interrupted) {
+           m->stat = Interrupted;
+         } else {
+           m->stat = Killed;
          }
          }
-         run_queue_tl = END_TSO_QUEUE;
-         /* ToDo: should I do the same with blocked queues? */
-          return Interrupted;
+         return;
+       }
       }
       }
+    }
+#endif
 
 
-      /* Put the thread back on the run queue, at the end.
-       * t->link is already set to END_TSO_QUEUE.
-       */
-      ASSERT(t->link == END_TSO_QUEUE);
-      if (run_queue_tl == END_TSO_QUEUE) {
-        run_queue_hd = run_queue_tl = t;
-      } else {
-        ASSERT(get_itbl(run_queue_tl)->type == TSO);
-       if (run_queue_hd == run_queue_tl) {
-         run_queue_hd->link = t;
-         run_queue_tl = t;
+    /* Top up the run queue from our spark pool.  We try to make the
+     * number of threads in the run queue equal to the number of
+     * free capabilities.
+     */
+#if defined(SMP)
+    {
+      nat n = n_free_capabilities;
+      StgTSO *tso = run_queue_hd;
+
+      /* Count the run queue */
+      while (n > 0 && tso != END_TSO_QUEUE) {
+       tso = tso->link;
+       n--;
+      }
+
+      for (; n > 0; n--) {
+       StgClosure *spark;
+       spark = findSpark(rtsFalse);
+       if (spark == NULL) {
+         break; /* no more sparks in the pool */
        } else {
        } else {
-         run_queue_tl->link = t;
-         run_queue_tl = t;
+         /* I'd prefer this to be done in activateSpark -- HWL */
+         /* tricky - it needs to hold the scheduler lock and
+          * not try to re-acquire it -- SDM */
+         createSparkThread(spark);       
+         IF_DEBUG(scheduler,
+                  sched_belch("==^^ turning spark of closure %p into a thread",
+                              (StgClosure *)spark));
        }
       }
        }
       }
-      break;
-
-    case ThreadBlocked:
-      IF_DEBUG(scheduler,belch("Thread %ld stopped, blocking\n", t->id));
-      threadPaused(t);
-      /* assume the thread has put itself on some blocked queue
-       * somewhere.
+      /* We need to wake up the other tasks if we just created some
+       * work for them.
        */
        */
-      break;
-
-    case ThreadFinished:
-      IF_DEBUG(scheduler,belch("Thread %ld finished\n", t->id));
-      t->whatNext = ThreadComplete;
-      break;
+      if (n_free_capabilities - n > 1) {
+         pthread_cond_signal(&thread_ready_cond);
+      }
+    }
+#endif /* SMP */
 
 
-    default:
-      barf("schedule: invalid thread return code");
+    /* Check whether any waiting threads need to be woken up.  If the
+     * run queue is empty, and there are no other tasks running, we
+     * can wait indefinitely for something to happen.
+     * ToDo: what if another client comes along & requests another
+     * main thread?
+     */
+    if (blocked_queue_hd != END_TSO_QUEUE || sleeping_queue != END_TSO_QUEUE) {
+      awaitEvent(
+          (run_queue_hd == END_TSO_QUEUE)
+#ifdef SMP
+       && (n_free_capabilities == RtsFlags.ParFlags.nNodes)
+#endif
+       );
     }
     }
+    /* we can be interrupted while waiting for I/O... */
+    if (interrupted) continue;
 
     /* check for signals each time around the scheduler */
 
     /* check for signals each time around the scheduler */
-#ifndef __MINGW32__
+#ifndef mingw32_TARGET_OS
     if (signals_pending()) {
       start_signal_handlers();
     }
 #endif
     if (signals_pending()) {
       start_signal_handlers();
     }
 #endif
-    /* If our main thread has finished or been killed, return.
-     * If we were re-entered as a result of a _ccall_gc, then
-     * pop the blocked thread off the ccalling_threads stack back
-     * into CurrentTSO.
+
+    /* 
+     * Detect deadlock: when we have no threads to run, there are no
+     * threads waiting on I/O or sleeping, and all the other tasks are
+     * waiting for work, we must have a deadlock of some description.
+     *
+     * We first try to find threads blocked on themselves (ie. black
+     * holes), and generate NonTermination exceptions where necessary.
+     *
+     * If no threads are black holed, we have a deadlock situation, so
+     * inform all the main threads.
      */
      */
-    if ((*MainTSO)->whatNext == ThreadComplete
-       || (*MainTSO)->whatNext == ThreadKilled) {
-      next_main_thread--;
-      if (in_ccall_gc) {
-       CurrentTSO = ccalling_threads;
-       ccalling_threads = ccalling_threads->link;
-       /* remember to stub the link field of CurrentTSO */
-       CurrentTSO->link = END_TSO_QUEUE;
-      }
-      if ((*MainTSO)->whatNext == ThreadComplete) {
-       /* we finished successfully, fill in the return value */
-       if (ret_val) { *ret_val = (StgClosure *)(*MainTSO)->sp[0]; };
-       return Success;
-      } else {
-       return Killed;
-      }
+#ifdef SMP
+    if (blocked_queue_hd == END_TSO_QUEUE
+       && run_queue_hd == END_TSO_QUEUE
+       && sleeping_queue == END_TSO_QUEUE
+       && (n_free_capabilities == RtsFlags.ParFlags.nNodes))
+    {
+       IF_DEBUG(scheduler, sched_belch("deadlocked, checking for black holes..."));
+       detectBlackHoles();
+       if (run_queue_hd == END_TSO_QUEUE) {
+           StgMainThread *m;
+           for (m = main_threads; m != NULL; m = m->link) {
+               m->ret = NULL;
+               m->stat = Deadlock;
+               pthread_cond_broadcast(&m->wakeup);
+           }
+           main_threads = NULL;
+       }
     }
     }
-
-  next_thread:
-    t = run_queue_hd;
-    if (t != END_TSO_QUEUE) {
-      run_queue_hd = t->link;
-      t->link = END_TSO_QUEUE;
-      if (run_queue_hd == END_TSO_QUEUE) {
-       run_queue_tl = END_TSO_QUEUE;
-      }
+#elif defined(PAR)
+    /* ToDo: add deadlock detection in GUM (similar to SMP) -- HWL */
+#else /* ! SMP */
+    if (blocked_queue_hd == END_TSO_QUEUE
+       && run_queue_hd == END_TSO_QUEUE
+       && sleeping_queue == END_TSO_QUEUE)
+    {
+       IF_DEBUG(scheduler, sched_belch("deadlocked, checking for black holes..."));
+       detectBlackHoles();
+       if (run_queue_hd == END_TSO_QUEUE) {
+           StgMainThread *m = main_threads;
+           m->ret = NULL;
+           m->stat = Deadlock;
+           main_threads = m->link;
+           return;
+       }
     }
     }
-  }
-
-  if (blocked_queue_hd != END_TSO_QUEUE) {
-    return AllBlocked;
-  } else {
-    return Deadlock;
-  }
-}
-
-/* -----------------------------------------------------------------------------
-   Where are the roots that we know about?
+#endif
 
 
-        - all the threads on the runnable queue
-        - all the threads on the blocked queue
-       - all the thread currently executing a _ccall_GC
-        - all the "main threads"
-     
-   -------------------------------------------------------------------------- */
+#ifdef SMP
+    /* If there's a GC pending, don't do anything until it has
+     * completed.
+     */
+    if (ready_to_gc) {
+      IF_DEBUG(scheduler,sched_belch("waiting for GC"));
+      pthread_cond_wait(&gc_pending_cond, &sched_mutex);
+    }
+    
+    /* block until we've got a thread on the run queue and a free
+     * capability.
+     */
+    while (run_queue_hd == END_TSO_QUEUE || free_capabilities == NULL) {
+      IF_DEBUG(scheduler, sched_belch("waiting for work"));
+      pthread_cond_wait(&thread_ready_cond, &sched_mutex);
+      IF_DEBUG(scheduler, sched_belch("work now available"));
+    }
+#endif
 
 
-static void GetRoots(void)
-{
-  nat i;
+#if defined(GRAN)
 
 
-  run_queue_hd      = (StgTSO *)MarkRoot((StgClosure *)run_queue_hd);
-  run_queue_tl      = (StgTSO *)MarkRoot((StgClosure *)run_queue_tl);
+    if (RtsFlags.GranFlags.Light)
+      GranSimLight_enter_system(event, &ActiveTSO); // adjust ActiveTSO etc
 
 
-  blocked_queue_hd  = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_hd);
-  blocked_queue_tl  = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_tl);
+    /* adjust time based on time-stamp */
+    if (event->time > CurrentTime[CurrentProc] &&
+        event->evttype != ContinueThread)
+      CurrentTime[CurrentProc] = event->time;
+    
+    /* Deal with the idle PEs (may issue FindWork or MoveSpark events) */
+    if (!RtsFlags.GranFlags.Light)
+      handleIdlePEs();
+
+    IF_DEBUG(gran, fprintf(stderr, "GRAN: switch by event-type\n"));
+
+    /* main event dispatcher in GranSim */
+    switch (event->evttype) {
+      /* Should just be continuing execution */
+    case ContinueThread:
+      IF_DEBUG(gran, fprintf(stderr, "GRAN: doing ContinueThread\n"));
+      /* ToDo: check assertion
+      ASSERT(run_queue_hd != (StgTSO*)NULL &&
+            run_queue_hd != END_TSO_QUEUE);
+      */
+      /* Ignore ContinueThreads for fetching threads (if synchr comm) */
+      if (!RtsFlags.GranFlags.DoAsyncFetch &&
+         procStatus[CurrentProc]==Fetching) {
+       belch("ghuH: Spurious ContinueThread while Fetching ignored; TSO %d (%p) [PE %d]",
+             CurrentTSO->id, CurrentTSO, CurrentProc);
+       goto next_thread;
+      }        
+      /* Ignore ContinueThreads for completed threads */
+      if (CurrentTSO->what_next == ThreadComplete) {
+       belch("ghuH: found a ContinueThread event for completed thread %d (%p) [PE %d] (ignoring ContinueThread)", 
+             CurrentTSO->id, CurrentTSO, CurrentProc);
+       goto next_thread;
+      }        
+      /* Ignore ContinueThreads for threads that are being migrated */
+      if (PROCS(CurrentTSO)==Nowhere) { 
+       belch("ghuH: trying to run the migrating TSO %d (%p) [PE %d] (ignoring ContinueThread)",
+             CurrentTSO->id, CurrentTSO, CurrentProc);
+       goto next_thread;
+      }
+      /* The thread should be at the beginning of the run queue */
+      if (CurrentTSO!=run_queue_hds[CurrentProc]) { 
+       belch("ghuH: TSO %d (%p) [PE %d] is not at the start of the run_queue when doing a ContinueThread",
+             CurrentTSO->id, CurrentTSO, CurrentProc);
+       break; // run the thread anyway
+      }
+      /*
+      new_event(proc, proc, CurrentTime[proc],
+               FindWork,
+               (StgTSO*)NULL, (StgClosure*)NULL, (rtsSpark*)NULL);
+      goto next_thread; 
+      */ /* Catches superfluous CONTINUEs -- should be unnecessary */
+      break; // now actually run the thread; DaH Qu'vam yImuHbej 
+
+    case FetchNode:
+      do_the_fetchnode(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case GlobalBlock:
+      do_the_globalblock(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case FetchReply:
+      do_the_fetchreply(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case UnblockThread:   /* Move from the blocked queue to the tail of */
+      do_the_unblock(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case ResumeThread:  /* Move from the blocked queue to the tail of */
+      /* the runnable queue ( i.e. Qu' SImqa'lu') */ 
+      event->tso->gran.blocktime += 
+       CurrentTime[CurrentProc] - event->tso->gran.blockedat;
+      do_the_startthread(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case StartThread:
+      do_the_startthread(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case MoveThread:
+      do_the_movethread(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case MoveSpark:
+      do_the_movespark(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    case FindWork:
+      do_the_findwork(event);
+      goto next_thread;             /* handle next event in event queue  */
+      
+    default:
+      barf("Illegal event type %u\n", event->evttype);
+    }  /* switch */
+    
+    /* This point was scheduler_loop in the old RTS */
+
+    IF_DEBUG(gran, belch("GRAN: after main switch"));
+
+    TimeOfLastEvent = CurrentTime[CurrentProc];
+    TimeOfNextEvent = get_time_of_next_event();
+    IgnoreEvents=(TimeOfNextEvent==0); // HWL HACK
+    // CurrentTSO = ThreadQueueHd;
+
+    IF_DEBUG(gran, belch("GRAN: time of next event is: %ld", 
+                        TimeOfNextEvent));
+
+    if (RtsFlags.GranFlags.Light) 
+      GranSimLight_leave_system(event, &ActiveTSO); 
+
+    EndOfTimeSlice = CurrentTime[CurrentProc]+RtsFlags.GranFlags.time_slice;
+
+    IF_DEBUG(gran, 
+            belch("GRAN: end of time-slice is %#lx", EndOfTimeSlice));
+
+    /* in a GranSim setup the TSO stays on the run queue */
+    t = CurrentTSO;
+    /* Take a thread from the run queue. */
+    t = POP_RUN_QUEUE(); // take_off_run_queue(t);
+
+    IF_DEBUG(gran, 
+            fprintf(stderr, "GRAN: About to run current thread, which is\n");
+            G_TSO(t,5));
+
+    context_switch = 0; // turned on via GranYield, checking events and time slice
+
+    IF_DEBUG(gran, 
+            DumpGranEvent(GR_SCHEDULE, t));
+
+    procStatus[CurrentProc] = Busy;
+
+#elif defined(PAR)
+    if (PendingFetches != END_BF_QUEUE) {
+        processFetches();
+    }
+
+    /* ToDo: phps merge with spark activation above */
+    /* check whether we have local work and send requests if we have none */
+    if (EMPTY_RUN_QUEUE()) {  /* no runnable threads */
+      /* :-[  no local threads => look out for local sparks */
+      /* the spark pool for the current PE */
+      pool = &(MainRegTable.rSparks); // generalise to cap = &MainRegTable
+      if (advisory_thread_count < RtsFlags.ParFlags.maxThreads &&
+         pool->hd < pool->tl) {
+       /* 
+        * ToDo: add GC code check that we really have enough heap afterwards!!
+        * Old comment:
+        * If we're here (no runnable threads) and we have pending
+        * sparks, we must have a space problem.  Get enough space
+        * to turn one of those pending sparks into a
+        * thread... 
+        */
+
+       spark = findSpark(rtsFalse);                /* get a spark */
+       if (spark != (rtsSpark) NULL) {
+         tso = activateSpark(spark);       /* turn the spark into a thread */
+         IF_PAR_DEBUG(schedule,
+                      belch("==== schedule: Created TSO %d (%p); %d threads active",
+                            tso->id, tso, advisory_thread_count));
+
+         if (tso==END_TSO_QUEUE) { /* failed to activate spark->back to loop */
+           belch("==^^ failed to activate spark");
+           goto next_thread;
+         }               /* otherwise fall through & pick-up new tso */
+       } else {
+         IF_PAR_DEBUG(verbose,
+                      belch("==^^ no local sparks (spark pool contains only NFs: %d)", 
+                            spark_queue_len(pool)));
+         goto next_thread;
+       }
+      }
+
+      /* If we still have no work we need to send a FISH to get a spark
+        from another PE 
+      */
+      if (EMPTY_RUN_QUEUE()) {
+      /* =8-[  no local sparks => look for work on other PEs */
+       /*
+        * We really have absolutely no work.  Send out a fish
+        * (there may be some out there already), and wait for
+        * something to arrive.  We clearly can't run any threads
+        * until a SCHEDULE or RESUME arrives, and so that's what
+        * we're hoping to see.  (Of course, we still have to
+        * respond to other types of messages.)
+        */
+       TIME now = msTime() /*CURRENT_TIME*/;
+       IF_PAR_DEBUG(verbose, 
+                    belch("--  now=%ld", now));
+       IF_PAR_DEBUG(verbose,
+                    if (outstandingFishes < RtsFlags.ParFlags.maxFishes &&
+                        (last_fish_arrived_at!=0 &&
+                         last_fish_arrived_at+RtsFlags.ParFlags.fishDelay > now)) {
+                      belch("--$$ delaying FISH until %ld (last fish %ld, delay %ld, now %ld)",
+                            last_fish_arrived_at+RtsFlags.ParFlags.fishDelay,
+                            last_fish_arrived_at,
+                            RtsFlags.ParFlags.fishDelay, now);
+                    });
+       
+       if (outstandingFishes < RtsFlags.ParFlags.maxFishes &&
+           (last_fish_arrived_at==0 ||
+            (last_fish_arrived_at+RtsFlags.ParFlags.fishDelay <= now))) {
+         /* outstandingFishes is set in sendFish, processFish;
+            avoid flooding system with fishes via delay */
+         pe = choosePE();
+         sendFish(pe, mytid, NEW_FISH_AGE, NEW_FISH_HISTORY, 
+                  NEW_FISH_HUNGER);
+
+         // Global statistics: count no. of fishes
+         if (RtsFlags.ParFlags.ParStats.Global &&
+             RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
+           globalParStats.tot_fish_mess++;
+         }
+       }
+      
+       receivedFinish = processMessages();
+       goto next_thread;
+      }
+    } else if (PacketsWaiting()) {  /* Look for incoming messages */
+      receivedFinish = processMessages();
+    }
+
+    /* Now we are sure that we have some work available */
+    ASSERT(run_queue_hd != END_TSO_QUEUE);
+
+    /* Take a thread from the run queue, if we have work */
+    t = POP_RUN_QUEUE();  // take_off_run_queue(END_TSO_QUEUE);
+    IF_DEBUG(sanity,checkTSO(t));
+
+    /* ToDo: write something to the log-file
+    if (RTSflags.ParFlags.granSimStats && !sameThread)
+        DumpGranEvent(GR_SCHEDULE, RunnableThreadsHd);
+
+    CurrentTSO = t;
+    */
+    /* the spark pool for the current PE */
+    pool = &(MainRegTable.rSparks); // generalise to cap = &MainRegTable
+
+    IF_DEBUG(scheduler, 
+            belch("--=^ %d threads, %d sparks on [%#x]", 
+                  run_queue_len(), spark_queue_len(pool), CURRENT_PROC));
+
+#if 1
+    if (0 && RtsFlags.ParFlags.ParStats.Full && 
+       t && LastTSO && t->id != LastTSO->id && 
+       LastTSO->why_blocked == NotBlocked && 
+       LastTSO->what_next != ThreadComplete) {
+      // if previously scheduled TSO not blocked we have to record the context switch
+      DumpVeryRawGranEvent(TimeOfLastYield, CURRENT_PROC, CURRENT_PROC,
+                          GR_DESCHEDULE, LastTSO, (StgClosure *)NULL, 0, 0);
+    }
+
+    if (RtsFlags.ParFlags.ParStats.Full && 
+       (emitSchedule /* forced emit */ ||
+        (t && LastTSO && t->id != LastTSO->id))) {
+      /* 
+        we are running a different TSO, so write a schedule event to log file
+        NB: If we use fair scheduling we also have to write  a deschedule 
+            event for LastTSO; with unfair scheduling we know that the
+            previous tso has blocked whenever we switch to another tso, so
+            we don't need it in GUM for now
+      */
+      DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC,
+                      GR_SCHEDULE, t, (StgClosure *)NULL, 0, 0);
+      emitSchedule = rtsFalse;
+    }
+     
+#endif
+#else /* !GRAN && !PAR */
+  
+    /* grab a thread from the run queue
+     */
+    ASSERT(run_queue_hd != END_TSO_QUEUE);
+    t = POP_RUN_QUEUE();
+    IF_DEBUG(sanity,checkTSO(t));
+
+#endif
+    
+    /* grab a capability
+     */
+#ifdef SMP
+    cap = free_capabilities;
+    free_capabilities = cap->link;
+    n_free_capabilities--;
+#else
+    cap = &MainRegTable;
+#endif
+    
+    cap->rCurrentTSO = t;
+    
+    /* context switches are now initiated by the timer signal, unless
+     * the user specified "context switch as often as possible", with
+     * +RTS -C0
+     */
+    if (RtsFlags.ConcFlags.ctxtSwitchTicks == 0
+       && (run_queue_hd != END_TSO_QUEUE
+           || blocked_queue_hd != END_TSO_QUEUE
+           || sleeping_queue != END_TSO_QUEUE))
+       context_switch = 1;
+    else
+       context_switch = 0;
+
+    RELEASE_LOCK(&sched_mutex);
+
+    IF_DEBUG(scheduler, sched_belch("-->> Running TSO %ld (%p) %s ...", 
+                             t->id, t, whatNext_strs[t->what_next]));
+
+    /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
+    /* Run the current thread 
+     */
+    switch (cap->rCurrentTSO->what_next) {
+    case ThreadKilled:
+    case ThreadComplete:
+       /* Thread already finished, return to scheduler. */
+       ret = ThreadFinished;
+       break;
+    case ThreadEnterGHC:
+       ret = StgRun((StgFunPtr) stg_enterStackTop, cap);
+       break;
+    case ThreadRunGHC:
+       ret = StgRun((StgFunPtr) stg_returnToStackTop, cap);
+       break;
+    case ThreadEnterInterp:
+       ret = interpretBCO(cap);
+       break;
+    default:
+      barf("schedule: invalid what_next field");
+    }
+    /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
+    
+    /* Costs for the scheduler are assigned to CCS_SYSTEM */
+#ifdef PROFILING
+    CCCS = CCS_SYSTEM;
+#endif
+    
+    ACQUIRE_LOCK(&sched_mutex);
+
+#ifdef SMP
+    IF_DEBUG(scheduler,fprintf(stderr,"scheduler (task %ld): ", pthread_self()););
+#elif !defined(GRAN) && !defined(PAR)
+    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: "););
+#endif
+    t = cap->rCurrentTSO;
+    
+#if defined(PAR)
+    /* HACK 675: if the last thread didn't yield, make sure to print a 
+       SCHEDULE event to the log file when StgRunning the next thread, even
+       if it is the same one as before */
+    LastTSO = t; 
+    TimeOfLastYield = CURRENT_TIME;
+#endif
+
+    switch (ret) {
+    case HeapOverflow:
+#if defined(GRAN)
+      IF_DEBUG(gran, 
+              DumpGranEvent(GR_DESCHEDULE, t));
+      globalGranStats.tot_heapover++;
+#elif defined(PAR)
+      // IF_DEBUG(par, 
+      //DumpGranEvent(GR_DESCHEDULE, t);
+      globalParStats.tot_heapover++;
+#endif
+      /* make all the running tasks block on a condition variable,
+       * maybe set context_switch and wait till they all pile in,
+       * then have them wait on a GC condition variable.
+       */
+      IF_DEBUG(scheduler,belch("--<< thread %ld (%p; %s) stopped: HeapOverflow", 
+                              t->id, t, whatNext_strs[t->what_next]));
+      threadPaused(t);
+#if defined(GRAN)
+      ASSERT(!is_on_queue(t,CurrentProc));
+#elif defined(PAR)
+      /* Currently we emit a DESCHEDULE event before GC in GUM.
+         ToDo: either add separate event to distinguish SYSTEM time from rest
+              or just nuke this DESCHEDULE (and the following SCHEDULE) */
+      if (0 && RtsFlags.ParFlags.ParStats.Full) {
+       DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC,
+                        GR_DESCHEDULE, t, (StgClosure *)NULL, 0, 0);
+       emitSchedule = rtsTrue;
+      }
+#endif
+      
+      ready_to_gc = rtsTrue;
+      context_switch = 1;              /* stop other threads ASAP */
+      PUSH_ON_RUN_QUEUE(t);
+      /* actual GC is done at the end of the while loop */
+      break;
+      
+    case StackOverflow:
+#if defined(GRAN)
+      IF_DEBUG(gran, 
+              DumpGranEvent(GR_DESCHEDULE, t));
+      globalGranStats.tot_stackover++;
+#elif defined(PAR)
+      // IF_DEBUG(par, 
+      // DumpGranEvent(GR_DESCHEDULE, t);
+      globalParStats.tot_stackover++;
+#endif
+      IF_DEBUG(scheduler,belch("--<< thread %ld (%p; %s) stopped, StackOverflow", 
+                              t->id, t, whatNext_strs[t->what_next]));
+      /* just adjust the stack for this thread, then pop it back
+       * on the run queue.
+       */
+      threadPaused(t);
+      { 
+       StgMainThread *m;
+       /* enlarge the stack */
+       StgTSO *new_t = threadStackOverflow(t);
+       
+       /* This TSO has moved, so update any pointers to it from the
+        * main thread stack.  It better not be on any other queues...
+        * (it shouldn't be).
+        */
+       for (m = main_threads; m != NULL; m = m->link) {
+         if (m->tso == t) {
+           m->tso = new_t;
+         }
+       }
+       threadPaused(new_t);
+       PUSH_ON_RUN_QUEUE(new_t);
+      }
+      break;
+
+    case ThreadYielding:
+#if defined(GRAN)
+      IF_DEBUG(gran, 
+              DumpGranEvent(GR_DESCHEDULE, t));
+      globalGranStats.tot_yields++;
+#elif defined(PAR)
+      // IF_DEBUG(par, 
+      // DumpGranEvent(GR_DESCHEDULE, t);
+      globalParStats.tot_yields++;
+#endif
+      /* put the thread back on the run queue.  Then, if we're ready to
+       * GC, check whether this is the last task to stop.  If so, wake
+       * up the GC thread.  getThread will block during a GC until the
+       * GC is finished.
+       */
+      IF_DEBUG(scheduler,
+               if (t->what_next == ThreadEnterInterp) {
+                  /* ToDo: or maybe a timer expired when we were in Hugs?
+                   * or maybe someone hit ctrl-C
+                    */
+                   belch("--<< thread %ld (%p; %s) stopped to switch to Hugs", 
+                        t->id, t, whatNext_strs[t->what_next]);
+               } else {
+                   belch("--<< thread %ld (%p; %s) stopped, yielding", 
+                        t->id, t, whatNext_strs[t->what_next]);
+               }
+               );
+
+      threadPaused(t);
+
+      IF_DEBUG(sanity,
+              //belch("&& Doing sanity check on yielding TSO %ld.", t->id);
+              checkTSO(t));
+      ASSERT(t->link == END_TSO_QUEUE);
+#if defined(GRAN)
+      ASSERT(!is_on_queue(t,CurrentProc));
+
+      IF_DEBUG(sanity,
+              //belch("&& Doing sanity check on all ThreadQueues (and their TSOs).");
+              checkThreadQsSanity(rtsTrue));
+#endif
+#if defined(PAR)
+      if (RtsFlags.ParFlags.doFairScheduling) { 
+       /* this does round-robin scheduling; good for concurrency */
+       APPEND_TO_RUN_QUEUE(t);
+      } else {
+       /* this does unfair scheduling; good for parallelism */
+       PUSH_ON_RUN_QUEUE(t);
+      }
+#else
+      /* this does round-robin scheduling; good for concurrency */
+      APPEND_TO_RUN_QUEUE(t);
+#endif
+#if defined(GRAN)
+      /* add a ContinueThread event to actually process the thread */
+      new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
+               ContinueThread,
+               t, (StgClosure*)NULL, (rtsSpark*)NULL);
+      IF_GRAN_DEBUG(bq, 
+              belch("GRAN: eventq and runnableq after adding yielded thread to queue again:");
+              G_EVENTQ(0);
+              G_CURR_THREADQ(0));
+#endif /* GRAN */
+      break;
+      
+    case ThreadBlocked:
+#if defined(GRAN)
+      IF_DEBUG(scheduler,
+              belch("--<< thread %ld (%p; %s) stopped, blocking on node %p [PE %d] with BQ: ", 
+                              t->id, t, whatNext_strs[t->what_next], t->block_info.closure, (t->block_info.closure==(StgClosure*)NULL ? 99 : where_is(t->block_info.closure)));
+              if (t->block_info.closure!=(StgClosure*)NULL) print_bq(t->block_info.closure));
+
+      // ??? needed; should emit block before
+      IF_DEBUG(gran, 
+              DumpGranEvent(GR_DESCHEDULE, t)); 
+      prune_eventq(t, (StgClosure *)NULL); // prune ContinueThreads for t
+      /*
+       ngoq Dogh!
+      ASSERT(procStatus[CurrentProc]==Busy || 
+             ((procStatus[CurrentProc]==Fetching) && 
+             (t->block_info.closure!=(StgClosure*)NULL)));
+      if (run_queue_hds[CurrentProc] == END_TSO_QUEUE &&
+         !(!RtsFlags.GranFlags.DoAsyncFetch &&
+           procStatus[CurrentProc]==Fetching)) 
+       procStatus[CurrentProc] = Idle;
+      */
+#elif defined(PAR)
+      IF_DEBUG(scheduler,
+              belch("--<< thread %ld (%p; %s) stopped, blocking on node %p with BQ: ", 
+                    t->id, t, whatNext_strs[t->what_next], t->block_info.closure));
+      IF_PAR_DEBUG(bq,
+
+                  if (t->block_info.closure!=(StgClosure*)NULL) 
+                    print_bq(t->block_info.closure));
+
+      /* Send a fetch (if BlockedOnGA) and dump event to log file */
+      blockThread(t);
+
+      /* whatever we schedule next, we must log that schedule */
+      emitSchedule = rtsTrue;
+
+#else /* !GRAN */
+      /* don't need to do anything.  Either the thread is blocked on
+       * I/O, in which case we'll have called addToBlockedQueue
+       * previously, or it's blocked on an MVar or Blackhole, in which
+       * case it'll be on the relevant queue already.
+       */
+      IF_DEBUG(scheduler,
+              fprintf(stderr, "--<< thread %d (%p) stopped: ", t->id, t);
+              printThreadBlockage(t);
+              fprintf(stderr, "\n"));
+
+      /* Only for dumping event to log file 
+        ToDo: do I need this in GranSim, too?
+      blockThread(t);
+      */
+#endif
+      threadPaused(t);
+      break;
+      
+    case ThreadFinished:
+      /* Need to check whether this was a main thread, and if so, signal
+       * the task that started it with the return value.  If we have no
+       * more main threads, we probably need to stop all the tasks until
+       * we get a new one.
+       */
+      /* We also end up here if the thread kills itself with an
+       * uncaught exception, see Exception.hc.
+       */
+      IF_DEBUG(scheduler,belch("--++ thread %d (%p) finished", t->id, t));
+#if defined(GRAN)
+      endThread(t, CurrentProc); // clean-up the thread
+#elif defined(PAR)
+      /* For now all are advisory -- HWL */
+      //if(t->priority==AdvisoryPriority) ??
+      advisory_thread_count--;
+      
+# ifdef DIST
+      if(t->dist.priority==RevalPriority)
+       FinishReval(t);
+# endif
+      
+      if (RtsFlags.ParFlags.ParStats.Full &&
+         !RtsFlags.ParFlags.ParStats.Suppressed) 
+       DumpEndEvent(CURRENT_PROC, t, rtsFalse /* not mandatory */);
+#endif
+      break;
+      
+    default:
+      barf("schedule: invalid thread return code %d", (int)ret);
+    }
+    
+#ifdef SMP
+    cap->link = free_capabilities;
+    free_capabilities = cap;
+    n_free_capabilities++;
+#endif
+
+#ifdef SMP
+    if (ready_to_gc && n_free_capabilities == RtsFlags.ParFlags.nNodes) 
+#else
+    if (ready_to_gc) 
+#endif
+      {
+      /* everybody back, start the GC.
+       * Could do it in this thread, or signal a condition var
+       * to do it in another thread.  Either way, we need to
+       * broadcast on gc_pending_cond afterward.
+       */
+#ifdef SMP
+      IF_DEBUG(scheduler,sched_belch("doing GC"));
+#endif
+      GarbageCollect(GetRoots,rtsFalse);
+      ready_to_gc = rtsFalse;
+#ifdef SMP
+      pthread_cond_broadcast(&gc_pending_cond);
+#endif
+#if defined(GRAN)
+      /* add a ContinueThread event to continue execution of current thread */
+      new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
+               ContinueThread,
+               t, (StgClosure*)NULL, (rtsSpark*)NULL);
+      IF_GRAN_DEBUG(bq, 
+              fprintf(stderr, "GRAN: eventq and runnableq after Garbage collection:\n");
+              G_EVENTQ(0);
+              G_CURR_THREADQ(0));
+#endif /* GRAN */
+    }
+#if defined(GRAN)
+  next_thread:
+    IF_GRAN_DEBUG(unused,
+                 print_eventq(EventHd));
+
+    event = get_next_event();
+
+#elif defined(PAR)
+  next_thread:
+    /* ToDo: wait for next message to arrive rather than busy wait */
+
+#else /* GRAN */
+  /* not any more
+  next_thread:
+    t = take_off_run_queue(END_TSO_QUEUE);
+  */
+#endif /* GRAN */
+  } /* end of while(1) */
+  IF_PAR_DEBUG(verbose,
+              belch("== Leaving schedule() after having received Finish"));
+}
+
+/* ---------------------------------------------------------------------------
+ * deleteAllThreads():  kill all the live threads.
+ *
+ * This is used when we catch a user interrupt (^C), before performing
+ * any necessary cleanups and running finalizers.
+ * ------------------------------------------------------------------------- */
+   
+void deleteAllThreads ( void )
+{
+  StgTSO* t;
+  IF_DEBUG(scheduler,sched_belch("deleting all threads"));
+  for (t = run_queue_hd; t != END_TSO_QUEUE; t = t->link) {
+      deleteThread(t);
+  }
+  for (t = blocked_queue_hd; t != END_TSO_QUEUE; t = t->link) {
+      deleteThread(t);
+  }
+  for (t = sleeping_queue; t != END_TSO_QUEUE; t = t->link) {
+      deleteThread(t);
+  }
+  run_queue_hd = run_queue_tl = END_TSO_QUEUE;
+  blocked_queue_hd = blocked_queue_tl = END_TSO_QUEUE;
+  sleeping_queue = END_TSO_QUEUE;
+}
+
+/* startThread and  insertThread are now in GranSim.c -- HWL */
+
+//@node Suspend and Resume, Run queue code, Main scheduling loop, Main scheduling code
+//@subsection Suspend and Resume
+
+/* ---------------------------------------------------------------------------
+ * Suspending & resuming Haskell threads.
+ * 
+ * When making a "safe" call to C (aka _ccall_GC), the task gives back
+ * its capability before calling the C function.  This allows another
+ * task to pick up the capability and carry on running Haskell
+ * threads.  It also means that if the C call blocks, it won't lock
+ * the whole system.
+ *
+ * The Haskell thread making the C call is put to sleep for the
+ * duration of the call, on the susepended_ccalling_threads queue.  We
+ * give out a token to the task, which it can use to resume the thread
+ * on return from the C function.
+ * ------------------------------------------------------------------------- */
+   
+StgInt
+suspendThread( Capability *cap )
+{
+  nat tok;
+
+  ACQUIRE_LOCK(&sched_mutex);
+
+  IF_DEBUG(scheduler,
+          sched_belch("thread %d did a _ccall_gc", cap->rCurrentTSO->id));
+
+  threadPaused(cap->rCurrentTSO);
+  cap->rCurrentTSO->link = suspended_ccalling_threads;
+  suspended_ccalling_threads = cap->rCurrentTSO;
+
+  /* Use the thread ID as the token; it should be unique */
+  tok = cap->rCurrentTSO->id;
+
+#ifdef SMP
+  cap->link = free_capabilities;
+  free_capabilities = cap;
+  n_free_capabilities++;
+#endif
+
+  RELEASE_LOCK(&sched_mutex);
+  return tok; 
+}
+
+Capability *
+resumeThread( StgInt tok )
+{
+  StgTSO *tso, **prev;
+  Capability *cap;
+
+  ACQUIRE_LOCK(&sched_mutex);
+
+  prev = &suspended_ccalling_threads;
+  for (tso = suspended_ccalling_threads; 
+       tso != END_TSO_QUEUE; 
+       prev = &tso->link, tso = tso->link) {
+    if (tso->id == (StgThreadID)tok) {
+      *prev = tso->link;
+      break;
+    }
+  }
+  if (tso == END_TSO_QUEUE) {
+    barf("resumeThread: thread not found");
+  }
+  tso->link = END_TSO_QUEUE;
+
+#ifdef SMP
+  while (free_capabilities == NULL) {
+    IF_DEBUG(scheduler, sched_belch("waiting to resume"));
+    pthread_cond_wait(&thread_ready_cond, &sched_mutex);
+    IF_DEBUG(scheduler, sched_belch("resuming thread %d", tso->id));
+  }
+  cap = free_capabilities;
+  free_capabilities = cap->link;
+  n_free_capabilities--;
+#else  
+  cap = &MainRegTable;
+#endif
+
+  cap->rCurrentTSO = tso;
+
+  RELEASE_LOCK(&sched_mutex);
+  return cap;
+}
+
+
+/* ---------------------------------------------------------------------------
+ * Static functions
+ * ------------------------------------------------------------------------ */
+static void unblockThread(StgTSO *tso);
+
+/* ---------------------------------------------------------------------------
+ * Comparing Thread ids.
+ *
+ * This is used from STG land in the implementation of the
+ * instances of Eq/Ord for ThreadIds.
+ * ------------------------------------------------------------------------ */
+
+int cmp_thread(const StgTSO *tso1, const StgTSO *tso2) 
+{ 
+  StgThreadID id1 = tso1->id; 
+  StgThreadID id2 = tso2->id;
+  if (id1 < id2) return (-1);
+  if (id1 > id2) return 1;
+  return 0;
+}
+
+/* ---------------------------------------------------------------------------
+   Create a new thread.
+
+   The new thread starts with the given stack size.  Before the
+   scheduler can run, however, this thread needs to have a closure
+   (and possibly some arguments) pushed on its stack.  See
+   pushClosure() in Schedule.h.
+
+   createGenThread() and createIOThread() (in SchedAPI.h) are
+   convenient packaged versions of this function.
+
+   currently pri (priority) is only used in a GRAN setup -- HWL
+   ------------------------------------------------------------------------ */
+//@cindex createThread
+#if defined(GRAN)
+/*   currently pri (priority) is only used in a GRAN setup -- HWL */
+StgTSO *
+createThread(nat stack_size, StgInt pri)
+{
+  return createThread_(stack_size, rtsFalse, pri);
+}
+
+static StgTSO *
+createThread_(nat size, rtsBool have_lock, StgInt pri)
+{
+#else
+StgTSO *
+createThread(nat stack_size)
+{
+  return createThread_(stack_size, rtsFalse);
+}
+
+static StgTSO *
+createThread_(nat size, rtsBool have_lock)
+{
+#endif
+
+    StgTSO *tso;
+    nat stack_size;
+
+    /* First check whether we should create a thread at all */
+#if defined(PAR)
+  /* check that no more than RtsFlags.ParFlags.maxThreads threads are created */
+  if (advisory_thread_count >= RtsFlags.ParFlags.maxThreads) {
+    threadsIgnored++;
+    belch("{createThread}Daq ghuH: refusing to create another thread; no more than %d threads allowed (currently %d)",
+         RtsFlags.ParFlags.maxThreads, advisory_thread_count);
+    return END_TSO_QUEUE;
+  }
+  threadsCreated++;
+#endif
+
+#if defined(GRAN)
+  ASSERT(!RtsFlags.GranFlags.Light || CurrentProc==0);
+#endif
+
+  // ToDo: check whether size = stack_size - TSO_STRUCT_SIZEW
+
+  /* catch ridiculously small stack sizes */
+  if (size < MIN_STACK_WORDS + TSO_STRUCT_SIZEW) {
+    size = MIN_STACK_WORDS + TSO_STRUCT_SIZEW;
+  }
+
+  stack_size = size - TSO_STRUCT_SIZEW;
+
+  tso = (StgTSO *)allocate(size);
+  TICK_ALLOC_TSO(size-TSO_STRUCT_SIZEW, 0);
+
+  SET_HDR(tso, &stg_TSO_info, CCS_SYSTEM);
+#if defined(GRAN)
+  SET_GRAN_HDR(tso, ThisPE);
+#endif
+  tso->what_next     = ThreadEnterGHC;
+
+  /* tso->id needs to be unique.  For now we use a heavyweight mutex to
+   * protect the increment operation on next_thread_id.
+   * In future, we could use an atomic increment instead.
+   */
+  if (!have_lock) { ACQUIRE_LOCK(&sched_mutex); }
+  tso->id = next_thread_id++; 
+  if (!have_lock) { RELEASE_LOCK(&sched_mutex); }
+
+  tso->why_blocked  = NotBlocked;
+  tso->blocked_exceptions = NULL;
+
+  tso->stack_size   = stack_size;
+  tso->max_stack_size = round_to_mblocks(RtsFlags.GcFlags.maxStkSize) 
+                              - TSO_STRUCT_SIZEW;
+  tso->sp           = (P_)&(tso->stack) + stack_size;
+
+#ifdef PROFILING
+  tso->prof.CCCS = CCS_MAIN;
+#endif
+
+  /* put a stop frame on the stack */
+  tso->sp -= sizeofW(StgStopFrame);
+  SET_HDR((StgClosure*)tso->sp,(StgInfoTable *)&stg_stop_thread_info,CCS_SYSTEM);
+  tso->su = (StgUpdateFrame*)tso->sp;
+
+  // ToDo: check this
+#if defined(GRAN)
+  tso->link = END_TSO_QUEUE;
+  /* uses more flexible routine in GranSim */
+  insertThread(tso, CurrentProc);
+#else
+  /* In a non-GranSim setup the pushing of a TSO onto the runq is separated
+   * from its creation
+   */
+#endif
+
+#if defined(GRAN) 
+  if (RtsFlags.GranFlags.GranSimStats.Full) 
+    DumpGranEvent(GR_START,tso);
+#elif defined(PAR)
+  if (RtsFlags.ParFlags.ParStats.Full) 
+    DumpGranEvent(GR_STARTQ,tso);
+  /* HACk to avoid SCHEDULE 
+     LastTSO = tso; */
+#endif
+
+  /* Link the new thread on the global thread list.
+   */
+  tso->global_link = all_threads;
+  all_threads = tso;
+
+#if defined(DIST)
+  tso->dist.priority = MandatoryPriority; //by default that is...
+#endif
+
+#if defined(GRAN)
+  tso->gran.pri = pri;
+# if defined(DEBUG)
+  tso->gran.magic = TSO_MAGIC; // debugging only
+# endif
+  tso->gran.sparkname   = 0;
+  tso->gran.startedat   = CURRENT_TIME; 
+  tso->gran.exported    = 0;
+  tso->gran.basicblocks = 0;
+  tso->gran.allocs      = 0;
+  tso->gran.exectime    = 0;
+  tso->gran.fetchtime   = 0;
+  tso->gran.fetchcount  = 0;
+  tso->gran.blocktime   = 0;
+  tso->gran.blockcount  = 0;
+  tso->gran.blockedat   = 0;
+  tso->gran.globalsparks = 0;
+  tso->gran.localsparks  = 0;
+  if (RtsFlags.GranFlags.Light)
+    tso->gran.clock  = Now; /* local clock */
+  else
+    tso->gran.clock  = 0;
+
+  IF_DEBUG(gran,printTSO(tso));
+#elif defined(PAR)
+# if defined(DEBUG)
+  tso->par.magic = TSO_MAGIC; // debugging only
+# endif
+  tso->par.sparkname   = 0;
+  tso->par.startedat   = CURRENT_TIME; 
+  tso->par.exported    = 0;
+  tso->par.basicblocks = 0;
+  tso->par.allocs      = 0;
+  tso->par.exectime    = 0;
+  tso->par.fetchtime   = 0;
+  tso->par.fetchcount  = 0;
+  tso->par.blocktime   = 0;
+  tso->par.blockcount  = 0;
+  tso->par.blockedat   = 0;
+  tso->par.globalsparks = 0;
+  tso->par.localsparks  = 0;
+#endif
+
+#if defined(GRAN)
+  globalGranStats.tot_threads_created++;
+  globalGranStats.threads_created_on_PE[CurrentProc]++;
+  globalGranStats.tot_sq_len += spark_queue_len(CurrentProc);
+  globalGranStats.tot_sq_probes++;
+#elif defined(PAR)
+  // collect parallel global statistics (currently done together with GC stats)
+  if (RtsFlags.ParFlags.ParStats.Global &&
+      RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
+    //fprintf(stderr, "Creating thread %d @ %11.2f\n", tso->id, usertime()); 
+    globalParStats.tot_threads_created++;
+  }
+#endif 
+
+#if defined(GRAN)
+  IF_GRAN_DEBUG(pri,
+               belch("==__ schedule: Created TSO %d (%p);",
+                     CurrentProc, tso, tso->id));
+#elif defined(PAR)
+    IF_PAR_DEBUG(verbose,
+                belch("==__ schedule: Created TSO %d (%p); %d threads active",
+                      tso->id, tso, advisory_thread_count));
+#else
+  IF_DEBUG(scheduler,sched_belch("created thread %ld, stack size = %lx words", 
+                                tso->id, tso->stack_size));
+#endif    
+  return tso;
+}
+
+#if defined(PAR)
+/* RFP:
+   all parallel thread creation calls should fall through the following routine.
+*/
+StgTSO *
+createSparkThread(rtsSpark spark) 
+{ StgTSO *tso;
+  ASSERT(spark != (rtsSpark)NULL);
+  if (advisory_thread_count >= RtsFlags.ParFlags.maxThreads) 
+  { threadsIgnored++;
+    barf("{createSparkThread}Daq ghuH: refusing to create another thread; no more than %d threads allowed (currently %d)",
+         RtsFlags.ParFlags.maxThreads, advisory_thread_count);    
+    return END_TSO_QUEUE;
+  }
+  else
+  { threadsCreated++;
+    tso = createThread_(RtsFlags.GcFlags.initialStkSize, rtsTrue);
+    if (tso==END_TSO_QUEUE)    
+      barf("createSparkThread: Cannot create TSO");
+#if defined(DIST)
+    tso->priority = AdvisoryPriority;
+#endif
+    pushClosure(tso,spark);
+    PUSH_ON_RUN_QUEUE(tso);
+    advisory_thread_count++;    
+  }
+  return tso;
+}
+#endif
+
+/*
+  Turn a spark into a thread.
+  ToDo: fix for SMP (needs to acquire SCHED_MUTEX!)
+*/
+#if defined(PAR)
+//@cindex activateSpark
+StgTSO *
+activateSpark (rtsSpark spark) 
+{
+  StgTSO *tso;
+
+  tso = createSparkThread(spark);
+  if (RtsFlags.ParFlags.ParStats.Full) {   
+    //ASSERT(run_queue_hd == END_TSO_QUEUE); // I think ...
+    IF_PAR_DEBUG(verbose,
+                belch("==^^ activateSpark: turning spark of closure %p (%s) into a thread",
+                      (StgClosure *)spark, info_type((StgClosure *)spark)));
+  }
+  // ToDo: fwd info on local/global spark to thread -- HWL
+  // tso->gran.exported =  spark->exported;
+  // tso->gran.locked =   !spark->global;
+  // tso->gran.sparkname = spark->name;
+
+  return tso;
+}
+#endif
+
+/* ---------------------------------------------------------------------------
+ * scheduleThread()
+ *
+ * scheduleThread puts a thread on the head of the runnable queue.
+ * This will usually be done immediately after a thread is created.
+ * The caller of scheduleThread must create the thread using e.g.
+ * createThread and push an appropriate closure
+ * on this thread's stack before the scheduler is invoked.
+ * ------------------------------------------------------------------------ */
+
+void
+scheduleThread(StgTSO *tso)
+{
+  if (tso==END_TSO_QUEUE){    
+    schedule();
+    return;
+  }
+
+  ACQUIRE_LOCK(&sched_mutex);
+
+  /* Put the new thread on the head of the runnable queue.  The caller
+   * better push an appropriate closure on this thread's stack
+   * beforehand.  In the SMP case, the thread may start running as
+   * soon as we release the scheduler lock below.
+   */
+  PUSH_ON_RUN_QUEUE(tso);
+  THREAD_RUNNABLE();
+
+#if 0
+  IF_DEBUG(scheduler,printTSO(tso));
+#endif
+  RELEASE_LOCK(&sched_mutex);
+}
+
+/* ---------------------------------------------------------------------------
+ * startTasks()
+ *
+ * Start up Posix threads to run each of the scheduler tasks.
+ * I believe the task ids are not needed in the system as defined.
+ *  KH @ 25/10/99
+ * ------------------------------------------------------------------------ */
+
+#if defined(PAR) || defined(SMP)
+void
+taskStart(void) /*  ( void *arg STG_UNUSED)  */
+{
+  scheduleThread(END_TSO_QUEUE);
+}
+#endif
+
+/* ---------------------------------------------------------------------------
+ * initScheduler()
+ *
+ * Initialise the scheduler.  This resets all the queues - if the
+ * queues contained any threads, they'll be garbage collected at the
+ * next pass.
+ *
+ * This now calls startTasks(), so should only be called once!  KH @ 25/10/99
+ * ------------------------------------------------------------------------ */
+
+#ifdef SMP
+static void
+term_handler(int sig STG_UNUSED)
+{
+  stat_workerStop();
+  ACQUIRE_LOCK(&term_mutex);
+  await_death--;
+  RELEASE_LOCK(&term_mutex);
+  pthread_exit(NULL);
+}
+#endif
+
+//@cindex initScheduler
+void 
+initScheduler(void)
+{
+#if defined(GRAN)
+  nat i;
+
+  for (i=0; i<=MAX_PROC; i++) {
+    run_queue_hds[i]      = END_TSO_QUEUE;
+    run_queue_tls[i]      = END_TSO_QUEUE;
+    blocked_queue_hds[i]  = END_TSO_QUEUE;
+    blocked_queue_tls[i]  = END_TSO_QUEUE;
+    ccalling_threadss[i]  = END_TSO_QUEUE;
+    sleeping_queue        = END_TSO_QUEUE;
+  }
+#else
+  run_queue_hd      = END_TSO_QUEUE;
+  run_queue_tl      = END_TSO_QUEUE;
+  blocked_queue_hd  = END_TSO_QUEUE;
+  blocked_queue_tl  = END_TSO_QUEUE;
+  sleeping_queue    = END_TSO_QUEUE;
+#endif 
+
+  suspended_ccalling_threads  = END_TSO_QUEUE;
+
+  main_threads = NULL;
+  all_threads  = END_TSO_QUEUE;
+
+  context_switch = 0;
+  interrupted    = 0;
+
+  RtsFlags.ConcFlags.ctxtSwitchTicks =
+      RtsFlags.ConcFlags.ctxtSwitchTime / TICK_MILLISECS;
+
+  /* Install the SIGHUP handler */
+#ifdef SMP
+  {
+    struct sigaction action,oact;
+
+    action.sa_handler = term_handler;
+    sigemptyset(&action.sa_mask);
+    action.sa_flags = 0;
+    if (sigaction(SIGTERM, &action, &oact) != 0) {
+      barf("can't install TERM handler");
+    }
+  }
+#endif
+
+#ifdef SMP
+  /* Allocate N Capabilities */
+  {
+    nat i;
+    Capability *cap, *prev;
+    cap  = NULL;
+    prev = NULL;
+    for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
+      cap = stgMallocBytes(sizeof(Capability), "initScheduler:capabilities");
+      cap->link = prev;
+      prev = cap;
+    }
+    free_capabilities = cap;
+    n_free_capabilities = RtsFlags.ParFlags.nNodes;
+  }
+  IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n",
+                            n_free_capabilities););
+#endif
+
+#if defined(SMP) || defined(PAR)
+  initSparkPools();
+#endif
+}
+
+#ifdef SMP
+void
+startTasks( void )
+{
+  nat i;
+  int r;
+  pthread_t tid;
+  
+  /* make some space for saving all the thread ids */
+  task_ids = stgMallocBytes(RtsFlags.ParFlags.nNodes * sizeof(task_info),
+                           "initScheduler:task_ids");
+  
+  /* and create all the threads */
+  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
+    r = pthread_create(&tid,NULL,taskStart,NULL);
+    if (r != 0) {
+      barf("startTasks: Can't create new Posix thread");
+    }
+    task_ids[i].id = tid;
+    task_ids[i].mut_time = 0.0;
+    task_ids[i].mut_etime = 0.0;
+    task_ids[i].gc_time = 0.0;
+    task_ids[i].gc_etime = 0.0;
+    task_ids[i].elapsedtimestart = elapsedtime();
+    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Started task: %ld\n",tid););
+  }
+}
+#endif
+
+void
+exitScheduler( void )
+{
+#ifdef SMP
+  nat i;
+
+  /* Don't want to use pthread_cancel, since we'd have to install
+   * these silly exception handlers (pthread_cleanup_{push,pop}) around
+   * all our locks.
+   */
+#if 0
+  /* Cancel all our tasks */
+  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
+    pthread_cancel(task_ids[i].id);
+  }
+  
+  /* Wait for all the tasks to terminate */
+  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
+    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: waiting for task %ld\n", 
+                              task_ids[i].id));
+    pthread_join(task_ids[i].id, NULL);
+  }
+#endif
+
+  /* Send 'em all a SIGHUP.  That should shut 'em up.
+   */
+  await_death = RtsFlags.ParFlags.nNodes;
+  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
+    pthread_kill(task_ids[i].id,SIGTERM);
+  }
+  while (await_death > 0) {
+    sched_yield();
+  }
+#endif
+}
+
+/* -----------------------------------------------------------------------------
+   Managing the per-task allocation areas.
+   
+   Each capability comes with an allocation area.  These are
+   fixed-length block lists into which allocation can be done.
+
+   ToDo: no support for two-space collection at the moment???
+   -------------------------------------------------------------------------- */
+
+/* -----------------------------------------------------------------------------
+ * waitThread is the external interface for running a new computation
+ * and waiting for the result.
+ *
+ * In the non-SMP case, we create a new main thread, push it on the 
+ * main-thread stack, and invoke the scheduler to run it.  The
+ * scheduler will return when the top main thread on the stack has
+ * completed or died, and fill in the necessary fields of the
+ * main_thread structure.
+ *
+ * In the SMP case, we create a main thread as before, but we then
+ * create a new condition variable and sleep on it.  When our new
+ * main thread has completed, we'll be woken up and the status/result
+ * will be in the main_thread struct.
+ * -------------------------------------------------------------------------- */
+
+int 
+howManyThreadsAvail ( void )
+{
+   int i = 0;
+   StgTSO* q;
+   for (q = run_queue_hd; q != END_TSO_QUEUE; q = q->link)
+      i++;
+   for (q = blocked_queue_hd; q != END_TSO_QUEUE; q = q->link)
+      i++;
+   for (q = sleeping_queue; q != END_TSO_QUEUE; q = q->link)
+      i++;
+   return i;
+}
+
+void
+finishAllThreads ( void )
+{
+   do {
+      while (run_queue_hd != END_TSO_QUEUE) {
+         waitThread ( run_queue_hd, NULL );
+      }
+      while (blocked_queue_hd != END_TSO_QUEUE) {
+         waitThread ( blocked_queue_hd, NULL );
+      }
+      while (sleeping_queue != END_TSO_QUEUE) {
+         waitThread ( blocked_queue_hd, NULL );
+      }
+   } while 
+      (blocked_queue_hd != END_TSO_QUEUE || 
+       run_queue_hd     != END_TSO_QUEUE ||
+       sleeping_queue   != END_TSO_QUEUE);
+}
+
+SchedulerStatus
+waitThread(StgTSO *tso, /*out*/StgClosure **ret)
+{
+  StgMainThread *m;
+  SchedulerStatus stat;
+
+  ACQUIRE_LOCK(&sched_mutex);
+  
+  m = stgMallocBytes(sizeof(StgMainThread), "waitThread");
+
+  m->tso = tso;
+  m->ret = ret;
+  m->stat = NoStatus;
+#ifdef SMP
+  pthread_cond_init(&m->wakeup, NULL);
+#endif
+
+  m->link = main_threads;
+  main_threads = m;
+
+  IF_DEBUG(scheduler, fprintf(stderr, "== scheduler: new main thread (%d)\n", 
+                             m->tso->id));
+
+#ifdef SMP
+  do {
+    pthread_cond_wait(&m->wakeup, &sched_mutex);
+  } while (m->stat == NoStatus);
+#elif defined(GRAN)
+  /* GranSim specific init */
+  CurrentTSO = m->tso;                // the TSO to run
+  procStatus[MainProc] = Busy;        // status of main PE
+  CurrentProc = MainProc;             // PE to run it on
+
+  schedule();
+#else
+  schedule();
+  ASSERT(m->stat != NoStatus);
+#endif
+
+  stat = m->stat;
+
+#ifdef SMP
+  pthread_cond_destroy(&m->wakeup);
+#endif
+
+  IF_DEBUG(scheduler, fprintf(stderr, "== scheduler: main thread (%d) finished\n", 
+                             m->tso->id));
+  free(m);
+
+  RELEASE_LOCK(&sched_mutex);
+
+  return stat;
+}
+
+//@node Run queue code, Garbage Collextion Routines, Suspend and Resume, Main scheduling code
+//@subsection Run queue code 
+
+#if 0
+/* 
+   NB: In GranSim we have many run queues; run_queue_hd is actually a macro
+       unfolding to run_queue_hds[CurrentProc], thus CurrentProc is an
+       implicit global variable that has to be correct when calling these
+       fcts -- HWL 
+*/
+
+/* Put the new thread on the head of the runnable queue.
+ * The caller of createThread better push an appropriate closure
+ * on this thread's stack before the scheduler is invoked.
+ */
+static /* inline */ void
+add_to_run_queue(tso)
+StgTSO* tso; 
+{
+  ASSERT(tso!=run_queue_hd && tso!=run_queue_tl);
+  tso->link = run_queue_hd;
+  run_queue_hd = tso;
+  if (run_queue_tl == END_TSO_QUEUE) {
+    run_queue_tl = tso;
+  }
+}
+
+/* Put the new thread at the end of the runnable queue. */
+static /* inline */ void
+push_on_run_queue(tso)
+StgTSO* tso; 
+{
+  ASSERT(get_itbl((StgClosure *)tso)->type == TSO);
+  ASSERT(run_queue_hd!=NULL && run_queue_tl!=NULL);
+  ASSERT(tso!=run_queue_hd && tso!=run_queue_tl);
+  if (run_queue_hd == END_TSO_QUEUE) {
+    run_queue_hd = tso;
+  } else {
+    run_queue_tl->link = tso;
+  }
+  run_queue_tl = tso;
+}
+
+/* 
+   Should be inlined because it's used very often in schedule.  The tso
+   argument is actually only needed in GranSim, where we want to have the
+   possibility to schedule *any* TSO on the run queue, irrespective of the
+   actual ordering. Therefore, if tso is not the nil TSO then we traverse
+   the run queue and dequeue the tso, adjusting the links in the queue. 
+*/
+//@cindex take_off_run_queue
+static /* inline */ StgTSO*
+take_off_run_queue(StgTSO *tso) {
+  StgTSO *t, *prev;
+
+  /* 
+     qetlaHbogh Qu' ngaSbogh ghomDaQ {tso} yIteq!
+
+     if tso is specified, unlink that tso from the run_queue (doesn't have
+     to be at the beginning of the queue); GranSim only 
+  */
+  if (tso!=END_TSO_QUEUE) {
+    /* find tso in queue */
+    for (t=run_queue_hd, prev=END_TSO_QUEUE; 
+        t!=END_TSO_QUEUE && t!=tso;
+        prev=t, t=t->link) 
+      /* nothing */ ;
+    ASSERT(t==tso);
+    /* now actually dequeue the tso */
+    if (prev!=END_TSO_QUEUE) {
+      ASSERT(run_queue_hd!=t);
+      prev->link = t->link;
+    } else {
+      /* t is at beginning of thread queue */
+      ASSERT(run_queue_hd==t);
+      run_queue_hd = t->link;
+    }
+    /* t is at end of thread queue */
+    if (t->link==END_TSO_QUEUE) {
+      ASSERT(t==run_queue_tl);
+      run_queue_tl = prev;
+    } else {
+      ASSERT(run_queue_tl!=t);
+    }
+    t->link = END_TSO_QUEUE;
+  } else {
+    /* take tso from the beginning of the queue; std concurrent code */
+    t = run_queue_hd;
+    if (t != END_TSO_QUEUE) {
+      run_queue_hd = t->link;
+      t->link = END_TSO_QUEUE;
+      if (run_queue_hd == END_TSO_QUEUE) {
+       run_queue_tl = END_TSO_QUEUE;
+      }
+    }
+  }
+  return t;
+}
+
+#endif /* 0 */
+
+//@node Garbage Collextion Routines, Blocking Queue Routines, Run queue code, Main scheduling code
+//@subsection Garbage Collextion Routines
+
+/* ---------------------------------------------------------------------------
+   Where are the roots that we know about?
+
+        - all the threads on the runnable queue
+        - all the threads on the blocked queue
+        - all the threads on the sleeping queue
+       - all the thread currently executing a _ccall_GC
+        - all the "main threads"
+     
+   ------------------------------------------------------------------------ */
+
+/* This has to be protected either by the scheduler monitor, or by the
+       garbage collection monitor (probably the latter).
+       KH @ 25/10/99
+*/
+
+static void GetRoots(void)
+{
+  StgMainThread *m;
+
+#if defined(GRAN)
+  {
+    nat i;
+    for (i=0; i<=RtsFlags.GranFlags.proc; i++) {
+      if ((run_queue_hds[i] != END_TSO_QUEUE) && ((run_queue_hds[i] != NULL)))
+       run_queue_hds[i]    = (StgTSO *)MarkRoot((StgClosure *)run_queue_hds[i]);
+      if ((run_queue_tls[i] != END_TSO_QUEUE) && ((run_queue_tls[i] != NULL)))
+       run_queue_tls[i]    = (StgTSO *)MarkRoot((StgClosure *)run_queue_tls[i]);
+      
+      if ((blocked_queue_hds[i] != END_TSO_QUEUE) && ((blocked_queue_hds[i] != NULL)))
+       blocked_queue_hds[i] = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_hds[i]);
+      if ((blocked_queue_tls[i] != END_TSO_QUEUE) && ((blocked_queue_tls[i] != NULL)))
+       blocked_queue_tls[i] = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_tls[i]);
+      if ((ccalling_threadss[i] != END_TSO_QUEUE) && ((ccalling_threadss[i] != NULL)))
+       ccalling_threadss[i] = (StgTSO *)MarkRoot((StgClosure *)ccalling_threadss[i]);
+    }
+  }
+
+  markEventQueue();
 
 
-  ccalling_threads  = (StgTSO *)MarkRoot((StgClosure *)ccalling_threads);
+#else /* !GRAN */
+  if (run_queue_hd != END_TSO_QUEUE) {
+    ASSERT(run_queue_tl != END_TSO_QUEUE);
+    run_queue_hd      = (StgTSO *)MarkRoot((StgClosure *)run_queue_hd);
+    run_queue_tl      = (StgTSO *)MarkRoot((StgClosure *)run_queue_tl);
+  }
+
+  if (blocked_queue_hd != END_TSO_QUEUE) {
+    ASSERT(blocked_queue_tl != END_TSO_QUEUE);
+    blocked_queue_hd  = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_hd);
+    blocked_queue_tl  = (StgTSO *)MarkRoot((StgClosure *)blocked_queue_tl);
+  }
 
 
-  for (i = 0; i < next_main_thread; i++) {
-    main_threads[i] = (StgTSO *)MarkRoot((StgClosure *)main_threads[i]);
+  if (sleeping_queue != END_TSO_QUEUE) {
+    sleeping_queue  = (StgTSO *)MarkRoot((StgClosure *)sleeping_queue);
   }
   }
+#endif 
+
+  for (m = main_threads; m != NULL; m = m->link) {
+    m->tso = (StgTSO *)MarkRoot((StgClosure *)m->tso);
+  }
+  if (suspended_ccalling_threads != END_TSO_QUEUE)
+    suspended_ccalling_threads = 
+      (StgTSO *)MarkRoot((StgClosure *)suspended_ccalling_threads);
+
+#if defined(SMP) || defined(PAR) || defined(GRAN)
+  markSparkQueue();
+#endif
 }
 
 /* -----------------------------------------------------------------------------
 }
 
 /* -----------------------------------------------------------------------------
@@ -474,6 +2155,8 @@ static void GetRoots(void)
 
    It might be useful to provide an interface whereby the programmer
    can specify more roots (ToDo).
 
    It might be useful to provide an interface whereby the programmer
    can specify more roots (ToDo).
+   
+   This needs to be protected by the GC condition variable above.  KH.
    -------------------------------------------------------------------------- */
 
 void (*extra_roots)(void);
    -------------------------------------------------------------------------- */
 
 void (*extra_roots)(void);
@@ -481,7 +2164,13 @@ void (*extra_roots)(void);
 void
 performGC(void)
 {
 void
 performGC(void)
 {
-  GarbageCollect(GetRoots);
+  GarbageCollect(GetRoots,rtsFalse);
+}
+
+void
+performMajorGC(void)
+{
+  GarbageCollect(GetRoots,rtsTrue);
 }
 
 static void
 }
 
 static void
@@ -496,15 +2185,16 @@ performGCWithRoots(void (*get_roots)(void))
 {
   extra_roots = get_roots;
 
 {
   extra_roots = get_roots;
 
-  GarbageCollect(AllRoots);
+  GarbageCollect(AllRoots,rtsFalse);
 }
 
 /* -----------------------------------------------------------------------------
    Stack overflow
 
 }
 
 /* -----------------------------------------------------------------------------
    Stack overflow
 
-   If the thread has reached its maximum stack size,
-   then bomb out.  Otherwise relocate the TSO into a larger chunk of
-   memory and adjust its stack size appropriately.
+   If the thread has reached its maximum stack size, then raise the
+   StackOverflow exception in the offending thread.  Otherwise
+   relocate the TSO into a larger chunk of memory and adjust its stack
+   size appropriately.
    -------------------------------------------------------------------------- */
 
 static StgTSO *
    -------------------------------------------------------------------------- */
 
 static StgTSO *
@@ -514,19 +2204,18 @@ threadStackOverflow(StgTSO *tso)
   StgPtr new_sp;
   StgTSO *dest;
 
   StgPtr new_sp;
   StgTSO *dest;
 
+  IF_DEBUG(sanity,checkTSO(tso));
   if (tso->stack_size >= tso->max_stack_size) {
   if (tso->stack_size >= tso->max_stack_size) {
-#if 0
-    /* If we're debugging, just print out the top of the stack */
-    printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size, 
-                                    tso->sp+64));
-#endif
-#ifdef INTERPRETER
-    fprintf(stderr, "fatal: stack overflow in Hugs; aborting\n" );
-    exit(1);
-#else
+
+    IF_DEBUG(gc,
+            belch("@@ threadStackOverflow of TSO %d (%p): stack too large (now %ld; max is %ld",
+                  tso->id, tso, tso->stack_size, tso->max_stack_size);
+            /* If we're debugging, just print out the top of the stack */
+            printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size, 
+                                             tso->sp+64)));
+
     /* Send this thread the StackOverflow exception */
     /* Send this thread the StackOverflow exception */
-    raiseAsync(tso, (StgClosure *)&stackOverflow_closure);
-#endif
+    raiseAsync(tso, (StgClosure *)stackOverflow_closure);
     return tso;
   }
 
     return tso;
   }
 
@@ -540,73 +2229,356 @@ threadStackOverflow(StgTSO *tso)
   new_tso_size = round_to_mblocks(new_tso_size);  /* Be MBLOCK-friendly */
   new_stack_size = new_tso_size - TSO_STRUCT_SIZEW;
 
   new_tso_size = round_to_mblocks(new_tso_size);  /* Be MBLOCK-friendly */
   new_stack_size = new_tso_size - TSO_STRUCT_SIZEW;
 
-  IF_DEBUG(scheduler, fprintf(stderr,"increasing stack size from %d words to %d.\n", tso->stack_size, new_stack_size));
+  IF_DEBUG(scheduler, fprintf(stderr,"== scheduler: increasing stack size from %d words to %d.\n", tso->stack_size, new_stack_size));
 
   dest = (StgTSO *)allocate(new_tso_size);
   TICK_ALLOC_TSO(new_tso_size-sizeofW(StgTSO),0);
 
 
   dest = (StgTSO *)allocate(new_tso_size);
   TICK_ALLOC_TSO(new_tso_size-sizeofW(StgTSO),0);
 
-  /* copy the TSO block and the old stack into the new area */
-  memcpy(dest,tso,TSO_STRUCT_SIZE);
-  stack_words = tso->stack + tso->stack_size - tso->sp;
-  new_sp = (P_)dest + new_tso_size - stack_words;
-  memcpy(new_sp, tso->sp, stack_words * sizeof(W_));
+  /* copy the TSO block and the old stack into the new area */
+  memcpy(dest,tso,TSO_STRUCT_SIZE);
+  stack_words = tso->stack + tso->stack_size - tso->sp;
+  new_sp = (P_)dest + new_tso_size - stack_words;
+  memcpy(new_sp, tso->sp, stack_words * sizeof(W_));
+
+  /* relocate the stack pointers... */
+  diff = (P_)new_sp - (P_)tso->sp; /* In *words* */
+  dest->su    = (StgUpdateFrame *) ((P_)dest->su + diff);
+  dest->sp    = new_sp;
+  dest->stack_size = new_stack_size;
+       
+  /* and relocate the update frame list */
+  relocate_TSO(tso, dest);
+
+  /* Mark the old TSO as relocated.  We have to check for relocated
+   * TSOs in the garbage collector and any primops that deal with TSOs.
+   *
+   * It's important to set the sp and su values to just beyond the end
+   * of the stack, so we don't attempt to scavenge any part of the
+   * dead TSO's stack.
+   */
+  tso->what_next = ThreadRelocated;
+  tso->link = dest;
+  tso->sp = (P_)&(tso->stack[tso->stack_size]);
+  tso->su = (StgUpdateFrame *)tso->sp;
+  tso->why_blocked = NotBlocked;
+  dest->mut_link = NULL;
+
+  IF_PAR_DEBUG(verbose,
+              belch("@@ threadStackOverflow of TSO %d (now at %p): stack size increased to %ld",
+                    tso->id, tso, tso->stack_size);
+              /* If we're debugging, just print out the top of the stack */
+              printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size, 
+                                               tso->sp+64)));
+  
+  IF_DEBUG(sanity,checkTSO(tso));
+#if 0
+  IF_DEBUG(scheduler,printTSO(dest));
+#endif
+
+  return dest;
+}
+
+//@node Blocking Queue Routines, Exception Handling Routines, Garbage Collextion Routines, Main scheduling code
+//@subsection Blocking Queue Routines
+
+/* ---------------------------------------------------------------------------
+   Wake up a queue that was blocked on some resource.
+   ------------------------------------------------------------------------ */
+
+#if defined(GRAN)
+static inline void
+unblockCount ( StgBlockingQueueElement *bqe, StgClosure *node )
+{
+}
+#elif defined(PAR)
+static inline void
+unblockCount ( StgBlockingQueueElement *bqe, StgClosure *node )
+{
+  /* write RESUME events to log file and
+     update blocked and fetch time (depending on type of the orig closure) */
+  if (RtsFlags.ParFlags.ParStats.Full) {
+    DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC, 
+                    GR_RESUMEQ, ((StgTSO *)bqe), ((StgTSO *)bqe)->block_info.closure,
+                    0, 0 /* spark_queue_len(ADVISORY_POOL) */);
+    if (EMPTY_RUN_QUEUE())
+      emitSchedule = rtsTrue;
+
+    switch (get_itbl(node)->type) {
+       case FETCH_ME_BQ:
+         ((StgTSO *)bqe)->par.fetchtime += CURRENT_TIME-((StgTSO *)bqe)->par.blockedat;
+         break;
+       case RBH:
+       case FETCH_ME:
+       case BLACKHOLE_BQ:
+         ((StgTSO *)bqe)->par.blocktime += CURRENT_TIME-((StgTSO *)bqe)->par.blockedat;
+         break;
+#ifdef DIST
+        case MVAR:
+          break;
+#endif   
+       default:
+         barf("{unblockOneLocked}Daq Qagh: unexpected closure in blocking queue");
+       }
+      }
+}
+#endif
+
+#if defined(GRAN)
+static StgBlockingQueueElement *
+unblockOneLocked(StgBlockingQueueElement *bqe, StgClosure *node)
+{
+    StgTSO *tso;
+    PEs node_loc, tso_loc;
+
+    node_loc = where_is(node); // should be lifted out of loop
+    tso = (StgTSO *)bqe;  // wastes an assignment to get the type right
+    tso_loc = where_is((StgClosure *)tso);
+    if (IS_LOCAL_TO(PROCS(node),tso_loc)) { // TSO is local
+      /* !fake_fetch => TSO is on CurrentProc is same as IS_LOCAL_TO */
+      ASSERT(CurrentProc!=node_loc || tso_loc==CurrentProc);
+      CurrentTime[CurrentProc] += RtsFlags.GranFlags.Costs.lunblocktime;
+      // insertThread(tso, node_loc);
+      new_event(tso_loc, tso_loc, CurrentTime[CurrentProc],
+               ResumeThread,
+               tso, node, (rtsSpark*)NULL);
+      tso->link = END_TSO_QUEUE; // overwrite link just to be sure 
+      // len_local++;
+      // len++;
+    } else { // TSO is remote (actually should be FMBQ)
+      CurrentTime[CurrentProc] += RtsFlags.GranFlags.Costs.mpacktime +
+                                  RtsFlags.GranFlags.Costs.gunblocktime +
+                                 RtsFlags.GranFlags.Costs.latency;
+      new_event(tso_loc, CurrentProc, CurrentTime[CurrentProc],
+               UnblockThread,
+               tso, node, (rtsSpark*)NULL);
+      tso->link = END_TSO_QUEUE; // overwrite link just to be sure 
+      // len++;
+    }
+    /* the thread-queue-overhead is accounted for in either Resume or UnblockThread */
+    IF_GRAN_DEBUG(bq,
+                 fprintf(stderr," %s TSO %d (%p) [PE %d] (block_info.closure=%p) (next=%p) ,",
+                         (node_loc==tso_loc ? "Local" : "Global"), 
+                         tso->id, tso, CurrentProc, tso->block_info.closure, tso->link));
+    tso->block_info.closure = NULL;
+    IF_DEBUG(scheduler,belch("-- Waking up thread %ld (%p)", 
+                            tso->id, tso));
+}
+#elif defined(PAR)
+static StgBlockingQueueElement *
+unblockOneLocked(StgBlockingQueueElement *bqe, StgClosure *node)
+{
+    StgBlockingQueueElement *next;
+
+    switch (get_itbl(bqe)->type) {
+    case TSO:
+      ASSERT(((StgTSO *)bqe)->why_blocked != NotBlocked);
+      /* if it's a TSO just push it onto the run_queue */
+      next = bqe->link;
+      // ((StgTSO *)bqe)->link = END_TSO_QUEUE; // debugging?
+      PUSH_ON_RUN_QUEUE((StgTSO *)bqe); 
+      THREAD_RUNNABLE();
+      unblockCount(bqe, node);
+      /* reset blocking status after dumping event */
+      ((StgTSO *)bqe)->why_blocked = NotBlocked;
+      break;
+
+    case BLOCKED_FETCH:
+      /* if it's a BLOCKED_FETCH put it on the PendingFetches list */
+      next = bqe->link;
+      bqe->link = (StgBlockingQueueElement *)PendingFetches;
+      PendingFetches = (StgBlockedFetch *)bqe;
+      break;
+
+# if defined(DEBUG)
+      /* can ignore this case in a non-debugging setup; 
+        see comments on RBHSave closures above */
+    case CONSTR:
+      /* check that the closure is an RBHSave closure */
+      ASSERT(get_itbl((StgClosure *)bqe) == &stg_RBH_Save_0_info ||
+            get_itbl((StgClosure *)bqe) == &stg_RBH_Save_1_info ||
+            get_itbl((StgClosure *)bqe) == &stg_RBH_Save_2_info);
+      break;
+
+    default:
+      barf("{unblockOneLocked}Daq Qagh: Unexpected IP (%#lx; %s) in blocking queue at %#lx\n",
+          get_itbl((StgClosure *)bqe), info_type((StgClosure *)bqe), 
+          (StgClosure *)bqe);
+# endif
+    }
+  IF_PAR_DEBUG(bq, fprintf(stderr, ", %p (%s)", bqe, info_type((StgClosure*)bqe)));
+  return next;
+}
+
+#else /* !GRAN && !PAR */
+static StgTSO *
+unblockOneLocked(StgTSO *tso)
+{
+  StgTSO *next;
+
+  ASSERT(get_itbl(tso)->type == TSO);
+  ASSERT(tso->why_blocked != NotBlocked);
+  tso->why_blocked = NotBlocked;
+  next = tso->link;
+  PUSH_ON_RUN_QUEUE(tso);
+  THREAD_RUNNABLE();
+  IF_DEBUG(scheduler,sched_belch("waking up thread %ld", tso->id));
+  return next;
+}
+#endif
+
+#if defined(GRAN) || defined(PAR)
+inline StgBlockingQueueElement *
+unblockOne(StgBlockingQueueElement *bqe, StgClosure *node)
+{
+  ACQUIRE_LOCK(&sched_mutex);
+  bqe = unblockOneLocked(bqe, node);
+  RELEASE_LOCK(&sched_mutex);
+  return bqe;
+}
+#else
+inline StgTSO *
+unblockOne(StgTSO *tso)
+{
+  ACQUIRE_LOCK(&sched_mutex);
+  tso = unblockOneLocked(tso);
+  RELEASE_LOCK(&sched_mutex);
+  return tso;
+}
+#endif
+
+#if defined(GRAN)
+void 
+awakenBlockedQueue(StgBlockingQueueElement *q, StgClosure *node)
+{
+  StgBlockingQueueElement *bqe;
+  PEs node_loc;
+  nat len = 0; 
+
+  IF_GRAN_DEBUG(bq, 
+               belch("##-_ AwBQ for node %p on PE %d @ %ld by TSO %d (%p): ", \
+                     node, CurrentProc, CurrentTime[CurrentProc], 
+                     CurrentTSO->id, CurrentTSO));
+
+  node_loc = where_is(node);
+
+  ASSERT(q == END_BQ_QUEUE ||
+        get_itbl(q)->type == TSO ||   // q is either a TSO or an RBHSave
+        get_itbl(q)->type == CONSTR); // closure (type constructor)
+  ASSERT(is_unique(node));
+
+  /* FAKE FETCH: magically copy the node to the tso's proc;
+     no Fetch necessary because in reality the node should not have been 
+     moved to the other PE in the first place
+  */
+  if (CurrentProc!=node_loc) {
+    IF_GRAN_DEBUG(bq, 
+                 belch("## node %p is on PE %d but CurrentProc is %d (TSO %d); assuming fake fetch and adjusting bitmask (old: %#x)",
+                       node, node_loc, CurrentProc, CurrentTSO->id, 
+                       // CurrentTSO, where_is(CurrentTSO),
+                       node->header.gran.procs));
+    node->header.gran.procs = (node->header.gran.procs) | PE_NUMBER(CurrentProc);
+    IF_GRAN_DEBUG(bq, 
+                 belch("## new bitmask of node %p is %#x",
+                       node, node->header.gran.procs));
+    if (RtsFlags.GranFlags.GranSimStats.Global) {
+      globalGranStats.tot_fake_fetches++;
+    }
+  }
+
+  bqe = q;
+  // ToDo: check: ASSERT(CurrentProc==node_loc);
+  while (get_itbl(bqe)->type==TSO) { // q != END_TSO_QUEUE) {
+    //next = bqe->link;
+    /* 
+       bqe points to the current element in the queue
+       next points to the next element in the queue
+    */
+    //tso = (StgTSO *)bqe;  // wastes an assignment to get the type right
+    //tso_loc = where_is(tso);
+    len++;
+    bqe = unblockOneLocked(bqe, node);
+  }
+
+  /* if this is the BQ of an RBH, we have to put back the info ripped out of
+     the closure to make room for the anchor of the BQ */
+  if (bqe!=END_BQ_QUEUE) {
+    ASSERT(get_itbl(node)->type == RBH && get_itbl(bqe)->type == CONSTR);
+    /*
+    ASSERT((info_ptr==&RBH_Save_0_info) ||
+          (info_ptr==&RBH_Save_1_info) ||
+          (info_ptr==&RBH_Save_2_info));
+    */
+    /* cf. convertToRBH in RBH.c for writing the RBHSave closure */
+    ((StgRBH *)node)->blocking_queue = (StgBlockingQueueElement *)((StgRBHSave *)bqe)->payload[0];
+    ((StgRBH *)node)->mut_link       = (StgMutClosure *)((StgRBHSave *)bqe)->payload[1];
+
+    IF_GRAN_DEBUG(bq,
+                 belch("## Filled in RBH_Save for %p (%s) at end of AwBQ",
+                       node, info_type(node)));
+  }
 
 
-  /* relocate the stack pointers... */
-  diff = (P_)new_sp - (P_)tso->sp; /* In *words* */
-  dest->su    = (StgUpdateFrame *) ((P_)dest->su + diff);
-  dest->sp    = new_sp;
-  dest->splim = (P_)dest->splim + (nat)((P_)dest - (P_)tso);
-  dest->stack_size = new_stack_size;
-       
-  /* and relocate the update frame list */
-  relocate_TSO(tso, dest);
+  /* statistics gathering */
+  if (RtsFlags.GranFlags.GranSimStats.Global) {
+    // globalGranStats.tot_bq_processing_time += bq_processing_time;
+    globalGranStats.tot_bq_len += len;      // total length of all bqs awakened
+    // globalGranStats.tot_bq_len_local += len_local;  // same for local TSOs only
+    globalGranStats.tot_awbq++;             // total no. of bqs awakened
+  }
+  IF_GRAN_DEBUG(bq,
+               fprintf(stderr,"## BQ Stats of %p: [%d entries] %s\n",
+                       node, len, (bqe!=END_BQ_QUEUE) ? "RBH" : ""));
+}
+#elif defined(PAR)
+void 
+awakenBlockedQueue(StgBlockingQueueElement *q, StgClosure *node)
+{
+  StgBlockingQueueElement *bqe;
 
 
-  /* Mark the old one as dead so we don't try to scavenge it during
-   * garbage collection (the TSO will likely be on a mutables list in
-   * some generation, but it'll get collected soon enough).  It's
-   * important to set the sp and su values to just beyond the end of
-   * the stack, so we don't attempt to scavenge any part of the dead
-   * TSO's stack.
-   */
-  tso->whatNext = ThreadKilled;
-  tso->sp = (P_)&(tso->stack[tso->stack_size]);
-  tso->su = (StgUpdateFrame *)tso->sp;
-  tso->blocked_on = NULL;
-  dest->mut_link = NULL;
+  ACQUIRE_LOCK(&sched_mutex);
 
 
-  IF_DEBUG(sanity,checkTSO(tso));
-#if 0
-  IF_DEBUG(scheduler,printTSO(dest));
+  IF_PAR_DEBUG(verbose, 
+              belch("##-_ AwBQ for node %p on [%x]: ",
+                    node, mytid));
+#ifdef DIST  
+  //RFP
+  if(get_itbl(q)->type == CONSTR || q==END_BQ_QUEUE) {
+    IF_PAR_DEBUG(verbose, belch("## ... nothing to unblock so lets just return. RFP (BUG?)"));
+    return;
+  }
 #endif
 #endif
-  if (tso == MainTSO) { /* hack */
-      MainTSO = dest;
+  
+  ASSERT(q == END_BQ_QUEUE ||
+        get_itbl(q)->type == TSO ||           
+        get_itbl(q)->type == BLOCKED_FETCH || 
+        get_itbl(q)->type == CONSTR); 
+
+  bqe = q;
+  while (get_itbl(bqe)->type==TSO || 
+        get_itbl(bqe)->type==BLOCKED_FETCH) {
+    bqe = unblockOneLocked(bqe, node);
   }
   }
-  return dest;
+  RELEASE_LOCK(&sched_mutex);
 }
 
 }
 
-/* -----------------------------------------------------------------------------
-   Wake up a queue that was blocked on some resource (usually a
-   computation in progress).
-   -------------------------------------------------------------------------- */
-
-void awaken_blocked_queue(StgTSO *q)
+#else   /* !GRAN && !PAR */
+void
+awakenBlockedQueue(StgTSO *tso)
 {
 {
-  StgTSO *tso;
-
-  while (q != END_TSO_QUEUE) {
-    ASSERT(get_itbl(q)->type == TSO);
-    tso = q;
-    q = tso->link;
-    PUSH_ON_RUN_QUEUE(tso);
-    tso->blocked_on = NULL;
-    IF_DEBUG(scheduler,belch("Waking up thread %ld", tso->id));
+  ACQUIRE_LOCK(&sched_mutex);
+  while (tso != END_TSO_QUEUE) {
+    tso = unblockOneLocked(tso);
   }
   }
+  RELEASE_LOCK(&sched_mutex);
 }
 }
+#endif
 
 
-/* -----------------------------------------------------------------------------
+//@node Exception Handling Routines, Debugging Routines, Blocking Queue Routines, Main scheduling code
+//@subsection Exception Handling Routines
+
+/* ---------------------------------------------------------------------------
    Interrupt execution
    - usually called inside a signal handler so it mustn't do anything fancy.   
    Interrupt execution
    - usually called inside a signal handler so it mustn't do anything fancy.   
-   -------------------------------------------------------------------------- */
+   ------------------------------------------------------------------------ */
 
 void
 interruptStgRts(void)
 
 void
 interruptStgRts(void)
@@ -620,23 +2592,161 @@ interruptStgRts(void)
 
    This is for use when we raise an exception in another thread, which
    may be blocked.
 
    This is for use when we raise an exception in another thread, which
    may be blocked.
+   This has nothing to do with the UnblockThread event in GranSim. -- HWL
    -------------------------------------------------------------------------- */
 
    -------------------------------------------------------------------------- */
 
+#if defined(GRAN) || defined(PAR)
+/*
+  NB: only the type of the blocking queue is different in GranSim and GUM
+      the operations on the queue-elements are the same
+      long live polymorphism!
+*/
 static void
 unblockThread(StgTSO *tso)
 {
 static void
 unblockThread(StgTSO *tso)
 {
-  StgTSO *t, **last;
+  StgBlockingQueueElement *t, **last;
 
 
-  if (tso->blocked_on == NULL) {
+  ACQUIRE_LOCK(&sched_mutex);
+  switch (tso->why_blocked) {
+
+  case NotBlocked:
     return;  /* not blocked */
     return;  /* not blocked */
+
+  case BlockedOnMVar:
+    ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
+    {
+      StgBlockingQueueElement *last_tso = END_BQ_QUEUE;
+      StgMVar *mvar = (StgMVar *)(tso->block_info.closure);
+
+      last = (StgBlockingQueueElement **)&mvar->head;
+      for (t = (StgBlockingQueueElement *)mvar->head; 
+          t != END_BQ_QUEUE; 
+          last = &t->link, last_tso = t, t = t->link) {
+       if (t == (StgBlockingQueueElement *)tso) {
+         *last = (StgBlockingQueueElement *)tso->link;
+         if (mvar->tail == tso) {
+           mvar->tail = (StgTSO *)last_tso;
+         }
+         goto done;
+       }
+      }
+      barf("unblockThread (MVAR): TSO not found");
+    }
+
+  case BlockedOnBlackHole:
+    ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
+    {
+      StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);
+
+      last = &bq->blocking_queue;
+      for (t = bq->blocking_queue; 
+          t != END_BQ_QUEUE; 
+          last = &t->link, t = t->link) {
+       if (t == (StgBlockingQueueElement *)tso) {
+         *last = (StgBlockingQueueElement *)tso->link;
+         goto done;
+       }
+      }
+      barf("unblockThread (BLACKHOLE): TSO not found");
+    }
+
+  case BlockedOnException:
+    {
+      StgTSO *target  = tso->block_info.tso;
+
+      ASSERT(get_itbl(target)->type == TSO);
+
+      if (target->what_next == ThreadRelocated) {
+         target = target->link;
+         ASSERT(get_itbl(target)->type == TSO);
+      }
+
+      ASSERT(target->blocked_exceptions != NULL);
+
+      last = (StgBlockingQueueElement **)&target->blocked_exceptions;
+      for (t = (StgBlockingQueueElement *)target->blocked_exceptions; 
+          t != END_BQ_QUEUE; 
+          last = &t->link, t = t->link) {
+       ASSERT(get_itbl(t)->type == TSO);
+       if (t == (StgBlockingQueueElement *)tso) {
+         *last = (StgBlockingQueueElement *)tso->link;
+         goto done;
+       }
+      }
+      barf("unblockThread (Exception): TSO not found");
+    }
+
+  case BlockedOnRead:
+  case BlockedOnWrite:
+    {
+      /* take TSO off blocked_queue */
+      StgBlockingQueueElement *prev = NULL;
+      for (t = (StgBlockingQueueElement *)blocked_queue_hd; t != END_BQ_QUEUE; 
+          prev = t, t = t->link) {
+       if (t == (StgBlockingQueueElement *)tso) {
+         if (prev == NULL) {
+           blocked_queue_hd = (StgTSO *)t->link;
+           if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
+             blocked_queue_tl = END_TSO_QUEUE;
+           }
+         } else {
+           prev->link = t->link;
+           if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
+             blocked_queue_tl = (StgTSO *)prev;
+           }
+         }
+         goto done;
+       }
+      }
+      barf("unblockThread (I/O): TSO not found");
+    }
+
+  case BlockedOnDelay:
+    {
+      /* take TSO off sleeping_queue */
+      StgBlockingQueueElement *prev = NULL;
+      for (t = (StgBlockingQueueElement *)sleeping_queue; t != END_BQ_QUEUE; 
+          prev = t, t = t->link) {
+       if (t == (StgBlockingQueueElement *)tso) {
+         if (prev == NULL) {
+           sleeping_queue = (StgTSO *)t->link;
+         } else {
+           prev->link = t->link;
+         }
+         goto done;
+       }
+      }
+      barf("unblockThread (I/O): TSO not found");
+    }
+
+  default:
+    barf("unblockThread");
   }
 
   }
 
-  switch (get_itbl(tso->blocked_on)->type) {
+ done:
+  tso->link = END_TSO_QUEUE;
+  tso->why_blocked = NotBlocked;
+  tso->block_info.closure = NULL;
+  PUSH_ON_RUN_QUEUE(tso);
+  RELEASE_LOCK(&sched_mutex);
+}
+#else
+static void
+unblockThread(StgTSO *tso)
+{
+  StgTSO *t, **last;
+
+  ACQUIRE_LOCK(&sched_mutex);
+  switch (tso->why_blocked) {
+
+  case NotBlocked:
+    return;  /* not blocked */
 
 
-  case MVAR:
+  case BlockedOnMVar:
+    ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
     {
       StgTSO *last_tso = END_TSO_QUEUE;
     {
       StgTSO *last_tso = END_TSO_QUEUE;
-      StgMVar *mvar = (StgMVar *)(tso->blocked_on);
+      StgMVar *mvar = (StgMVar *)(tso->block_info.closure);
 
       last = &mvar->head;
       for (t = mvar->head; t != END_TSO_QUEUE; 
 
       last = &mvar->head;
       for (t = mvar->head; t != END_TSO_QUEUE; 
@@ -652,9 +2762,10 @@ unblockThread(StgTSO *tso)
       barf("unblockThread (MVAR): TSO not found");
     }
 
       barf("unblockThread (MVAR): TSO not found");
     }
 
-  case BLACKHOLE_BQ:
+  case BlockedOnBlackHole:
+    ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
     {
     {
-      StgBlockingQueue *bq = (StgBlockingQueue *)(tso->blocked_on);
+      StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);
 
       last = &bq->blocking_queue;
       for (t = bq->blocking_queue; t != END_TSO_QUEUE; 
 
       last = &bq->blocking_queue;
       for (t = bq->blocking_queue; t != END_TSO_QUEUE; 
@@ -667,15 +2778,84 @@ unblockThread(StgTSO *tso)
       barf("unblockThread (BLACKHOLE): TSO not found");
     }
 
       barf("unblockThread (BLACKHOLE): TSO not found");
     }
 
+  case BlockedOnException:
+    {
+      StgTSO *target  = tso->block_info.tso;
+
+      ASSERT(get_itbl(target)->type == TSO);
+
+      while (target->what_next == ThreadRelocated) {
+         target = target->link;
+         ASSERT(get_itbl(target)->type == TSO);
+      }
+      
+      ASSERT(target->blocked_exceptions != NULL);
+
+      last = &target->blocked_exceptions;
+      for (t = target->blocked_exceptions; t != END_TSO_QUEUE; 
+          last = &t->link, t = t->link) {
+       ASSERT(get_itbl(t)->type == TSO);
+       if (t == tso) {
+         *last = tso->link;
+         goto done;
+       }
+      }
+      barf("unblockThread (Exception): TSO not found");
+    }
+
+  case BlockedOnRead:
+  case BlockedOnWrite:
+    {
+      StgTSO *prev = NULL;
+      for (t = blocked_queue_hd; t != END_TSO_QUEUE; 
+          prev = t, t = t->link) {
+       if (t == tso) {
+         if (prev == NULL) {
+           blocked_queue_hd = t->link;
+           if (blocked_queue_tl == t) {
+             blocked_queue_tl = END_TSO_QUEUE;
+           }
+         } else {
+           prev->link = t->link;
+           if (blocked_queue_tl == t) {
+             blocked_queue_tl = prev;
+           }
+         }
+         goto done;
+       }
+      }
+      barf("unblockThread (I/O): TSO not found");
+    }
+
+  case BlockedOnDelay:
+    {
+      StgTSO *prev = NULL;
+      for (t = sleeping_queue; t != END_TSO_QUEUE; 
+          prev = t, t = t->link) {
+       if (t == tso) {
+         if (prev == NULL) {
+           sleeping_queue = t->link;
+         } else {
+           prev->link = t->link;
+         }
+         goto done;
+       }
+      }
+      barf("unblockThread (I/O): TSO not found");
+    }
+
   default:
     barf("unblockThread");
   }
 
  done:
   tso->link = END_TSO_QUEUE;
   default:
     barf("unblockThread");
   }
 
  done:
   tso->link = END_TSO_QUEUE;
-  tso->blocked_on = NULL;
+  tso->why_blocked = NotBlocked;
+  tso->block_info.closure = NULL;
   PUSH_ON_RUN_QUEUE(tso);
   PUSH_ON_RUN_QUEUE(tso);
+  RELEASE_LOCK(&sched_mutex);
 }
 }
+#endif
 
 /* -----------------------------------------------------------------------------
  * raiseAsync()
 
 /* -----------------------------------------------------------------------------
  * raiseAsync()
@@ -722,11 +2902,11 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
   StgPtr          sp = tso->sp;
   
   /* Thread already dead? */
   StgPtr          sp = tso->sp;
   
   /* Thread already dead? */
-  if (tso->whatNext == ThreadComplete || tso->whatNext == ThreadKilled) {
+  if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
     return;
   }
 
     return;
   }
 
-  IF_DEBUG(scheduler, belch("Raising exception in thread %ld.", tso->id));
+  IF_DEBUG(scheduler, sched_belch("raising exception in thread %ld.", tso->id));
 
   /* Remove it from any blocking queues */
   unblockThread(tso);
 
   /* Remove it from any blocking queues */
   unblockThread(tso);
@@ -737,7 +2917,7 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
    * returns to the next return address on the stack.
    */
   if ( LOOKS_LIKE_GHC_INFO((void*)*sp) ) {
    * returns to the next return address on the stack.
    */
   if ( LOOKS_LIKE_GHC_INFO((void*)*sp) ) {
-    *(--sp) = (W_)&dummy_ret_closure;
+    *(--sp) = (W_)&stg_dummy_ret_closure;
   }
 
   while (1) {
   }
 
   while (1) {
@@ -746,31 +2926,53 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
     StgAP_UPD * ap;
 
     /* If we find a CATCH_FRAME, and we've got an exception to raise,
     StgAP_UPD * ap;
 
     /* If we find a CATCH_FRAME, and we've got an exception to raise,
-     * then build PAP(handler,exception), and leave it on top of
-     * the stack ready to enter.
+     * then build PAP(handler,exception,realworld#), and leave it on
+     * top of the stack ready to enter.
      */
     if (get_itbl(su)->type == CATCH_FRAME && exception != NULL) {
       StgCatchFrame *cf = (StgCatchFrame *)su;
       /* we've got an exception to raise, so let's pass it to the
        * handler in this frame.
        */
      */
     if (get_itbl(su)->type == CATCH_FRAME && exception != NULL) {
       StgCatchFrame *cf = (StgCatchFrame *)su;
       /* we've got an exception to raise, so let's pass it to the
        * handler in this frame.
        */
-      ap = (StgAP_UPD *)allocate(sizeofW(StgPAP) + 1);
-      TICK_ALLOC_UPD_PAP(2,0);
-      SET_HDR(ap,&PAP_info,cf->header.prof.ccs);
+      ap = (StgAP_UPD *)allocate(sizeofW(StgPAP) + 2);
+      TICK_ALLOC_UPD_PAP(3,0);
+      SET_HDR(ap,&stg_PAP_info,cf->header.prof.ccs);
              
              
-      ap->n_args = 1;
-      ap->fun = cf->handler;
-      ap->payload[0] = (P_)exception;
+      ap->n_args = 2;
+      ap->fun = cf->handler;   /* :: Exception -> IO a */
+      ap->payload[0] = exception;
+      ap->payload[1] = ARG_TAG(0); /* realworld token */
 
 
-      /* sp currently points to the word above the CATCH_FRAME on the
-       * stack.  Replace the CATCH_FRAME with a pointer to the new handler
-       * application.
+      /* throw away the stack from Sp up to and including the
+       * CATCH_FRAME.
        */
        */
-      sp += sizeofW(StgCatchFrame);
-      sp[0] = (W_)ap;
+      sp = (P_)su + sizeofW(StgCatchFrame) - 1; 
       tso->su = cf->link;
       tso->su = cf->link;
+
+      /* Restore the blocked/unblocked state for asynchronous exceptions
+       * at the CATCH_FRAME.  
+       *
+       * If exceptions were unblocked at the catch, arrange that they
+       * are unblocked again after executing the handler by pushing an
+       * unblockAsyncExceptions_ret stack frame.
+       */
+      if (!cf->exceptions_blocked) {
+       *(sp--) = (W_)&stg_unblockAsyncExceptionszh_ret_info;
+      }
+      
+      /* Ensure that async exceptions are blocked when running the handler.
+       */
+      if (tso->blocked_exceptions == NULL) {
+       tso->blocked_exceptions = END_TSO_QUEUE;
+      }
+      
+      /* Put the newly-built PAP on top of the stack, ready to execute
+       * when the thread restarts.
+       */
+      sp[0] = (W_)ap;
       tso->sp = sp;
       tso->sp = sp;
-      tso->whatNext = ThreadEnterGHC;
+      tso->what_next = ThreadEnterGHC;
+      IF_DEBUG(sanity, checkTSO(tso));
       return;
     }
 
       return;
     }
 
@@ -779,7 +2981,6 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
      * fun field.
      */
     ap = (StgAP_UPD *)allocate(AP_sizeW(words));
      * fun field.
      */
     ap = (StgAP_UPD *)allocate(AP_sizeW(words));
-    TICK_ALLOC_UP_THK(words+1,0);
     
     ASSERT(words >= 0);
     
     
     ASSERT(words >= 0);
     
@@ -787,17 +2988,18 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
     ap->fun    = (StgClosure *)sp[0];
     sp++;
     for(i=0; i < (nat)words; ++i) {
     ap->fun    = (StgClosure *)sp[0];
     sp++;
     for(i=0; i < (nat)words; ++i) {
-      ap->payload[i] = (P_)*sp++;
+      ap->payload[i] = (StgClosure *)*sp++;
     }
     
     switch (get_itbl(su)->type) {
       
     case UPDATE_FRAME:
       {
     }
     
     switch (get_itbl(su)->type) {
       
     case UPDATE_FRAME:
       {
-       SET_HDR(ap,&AP_UPD_info,su->header.prof.ccs /* ToDo */); 
+       SET_HDR(ap,&stg_AP_UPD_info,su->header.prof.ccs /* ToDo */); 
+       TICK_ALLOC_UP_THK(words+1,0);
        
        IF_DEBUG(scheduler,
        
        IF_DEBUG(scheduler,
-                fprintf(stderr,  "Updating ");
+                fprintf(stderr,  "scheduler: Updating ");
                 printPtr((P_)su->updatee); 
                 fprintf(stderr,  " with ");
                 printObj((StgClosure *)ap);
                 printPtr((P_)su->updatee); 
                 fprintf(stderr,  " with ");
                 printObj((StgClosure *)ap);
@@ -806,14 +3008,24 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
        /* Replace the updatee with an indirection - happily
         * this will also wake up any threads currently
         * waiting on the result.
        /* Replace the updatee with an indirection - happily
         * this will also wake up any threads currently
         * waiting on the result.
+        *
+        * Warning: if we're in a loop, more than one update frame on
+        * the stack may point to the same object.  Be careful not to
+        * overwrite an IND_OLDGEN in this case, because we'll screw
+        * up the mutable lists.  To be on the safe side, don't
+        * overwrite any kind of indirection at all.  See also
+        * threadSqueezeStack in GC.c, where we have to make a similar
+        * check.
         */
         */
-       UPD_IND(su->updatee,ap);  /* revert the black hole */
+       if (!closure_IND(su->updatee)) {
+           UPD_IND_NOLOCK(su->updatee,ap);  /* revert the black hole */
+       }
        su = su->link;
        sp += sizeofW(StgUpdateFrame) -1;
        sp[0] = (W_)ap; /* push onto stack */
        break;
       }
        su = su->link;
        sp += sizeofW(StgUpdateFrame) -1;
        sp[0] = (W_)ap; /* push onto stack */
        break;
       }
-      
+
     case CATCH_FRAME:
       {
        StgCatchFrame *cf = (StgCatchFrame *)su;
     case CATCH_FRAME:
       {
        StgCatchFrame *cf = (StgCatchFrame *)su;
@@ -822,17 +3034,18 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
        /* We want a PAP, not an AP_UPD.  Fortunately, the
         * layout's the same.
         */
        /* We want a PAP, not an AP_UPD.  Fortunately, the
         * layout's the same.
         */
-       SET_HDR(ap,&PAP_info,su->header.prof.ccs /* ToDo */);
+       SET_HDR(ap,&stg_PAP_info,su->header.prof.ccs /* ToDo */);
+       TICK_ALLOC_UPD_PAP(words+1,0);
        
        /* now build o = FUN(catch,ap,handler) */
        o = (StgClosure *)allocate(sizeofW(StgClosure)+2);
        
        /* now build o = FUN(catch,ap,handler) */
        o = (StgClosure *)allocate(sizeofW(StgClosure)+2);
-       TICK_ALLOC_SE_THK(2,0);
-       SET_HDR(o,&catch_info,su->header.prof.ccs /* ToDo */);
+       TICK_ALLOC_FUN(2,0);
+       SET_HDR(o,&stg_catch_info,su->header.prof.ccs /* ToDo */);
        o->payload[0] = (StgClosure *)ap;
        o->payload[1] = cf->handler;
        
        IF_DEBUG(scheduler,
        o->payload[0] = (StgClosure *)ap;
        o->payload[1] = cf->handler;
        
        IF_DEBUG(scheduler,
-                fprintf(stderr,  "Built ");
+                fprintf(stderr,  "scheduler: Built ");
                 printObj((StgClosure *)o);
                 );
        
                 printObj((StgClosure *)o);
                 );
        
@@ -848,16 +3061,17 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
        StgSeqFrame *sf = (StgSeqFrame *)su;
        StgClosure* o;
        
        StgSeqFrame *sf = (StgSeqFrame *)su;
        StgClosure* o;
        
-       SET_HDR(ap,&PAP_info,su->header.prof.ccs /* ToDo */);
+       SET_HDR(ap,&stg_PAP_info,su->header.prof.ccs /* ToDo */);
+       TICK_ALLOC_UPD_PAP(words+1,0);
        
        /* now build o = FUN(seq,ap) */
        o = (StgClosure *)allocate(sizeofW(StgClosure)+1);
        TICK_ALLOC_SE_THK(1,0);
        
        /* now build o = FUN(seq,ap) */
        o = (StgClosure *)allocate(sizeofW(StgClosure)+1);
        TICK_ALLOC_SE_THK(1,0);
-       SET_HDR(o,&seq_info,su->header.prof.ccs /* ToDo */);
-       payloadCPtr(o,0) = (StgClosure *)ap;
+       SET_HDR(o,&stg_seq_info,su->header.prof.ccs /* ToDo */);
+       o->payload[0] = (StgClosure *)ap;
        
        IF_DEBUG(scheduler,
        
        IF_DEBUG(scheduler,
-                fprintf(stderr,  "Built ");
+                fprintf(stderr,  "scheduler: Built ");
                 printObj((StgClosure *)o);
                 );
        
                 printObj((StgClosure *)o);
                 );
        
@@ -872,14 +3086,422 @@ raiseAsync(StgTSO *tso, StgClosure *exception)
       /* We've stripped the entire stack, the thread is now dead. */
       sp += sizeofW(StgStopFrame) - 1;
       sp[0] = (W_)exception;   /* save the exception */
       /* We've stripped the entire stack, the thread is now dead. */
       sp += sizeofW(StgStopFrame) - 1;
       sp[0] = (W_)exception;   /* save the exception */
-      tso->whatNext = ThreadKilled;
+      tso->what_next = ThreadKilled;
       tso->su = (StgUpdateFrame *)(sp+1);
       tso->sp = sp;
       return;
       tso->su = (StgUpdateFrame *)(sp+1);
       tso->sp = sp;
       return;
-      
+
     default:
       barf("raiseAsync");
     }
   }
   barf("raiseAsync");
 }
     default:
       barf("raiseAsync");
     }
   }
   barf("raiseAsync");
 }
+
+/* -----------------------------------------------------------------------------
+   resurrectThreads is called after garbage collection on the list of
+   threads found to be garbage.  Each of these threads will be woken
+   up and sent a signal: BlockedOnDeadMVar if the thread was blocked
+   on an MVar, or NonTermination if the thread was blocked on a Black
+   Hole.
+   -------------------------------------------------------------------------- */
+
+void
+resurrectThreads( StgTSO *threads )
+{
+  StgTSO *tso, *next;
+
+  for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
+    next = tso->global_link;
+    tso->global_link = all_threads;
+    all_threads = tso;
+    IF_DEBUG(scheduler, sched_belch("resurrecting thread %d", tso->id));
+
+    switch (tso->why_blocked) {
+    case BlockedOnMVar:
+    case BlockedOnException:
+      raiseAsync(tso,(StgClosure *)BlockedOnDeadMVar_closure);
+      break;
+    case BlockedOnBlackHole:
+      raiseAsync(tso,(StgClosure *)NonTermination_closure);
+      break;
+    case NotBlocked:
+      /* This might happen if the thread was blocked on a black hole
+       * belonging to a thread that we've just woken up (raiseAsync
+       * can wake up threads, remember...).
+       */
+      continue;
+    default:
+      barf("resurrectThreads: thread blocked in a strange way");
+    }
+  }
+}
+
+/* -----------------------------------------------------------------------------
+ * Blackhole detection: if we reach a deadlock, test whether any
+ * threads are blocked on themselves.  Any threads which are found to
+ * be self-blocked get sent a NonTermination exception.
+ *
+ * This is only done in a deadlock situation in order to avoid
+ * performance overhead in the normal case.
+ * -------------------------------------------------------------------------- */
+
+static void
+detectBlackHoles( void )
+{
+    StgTSO *t = all_threads;
+    StgUpdateFrame *frame;
+    StgClosure *blocked_on;
+
+    for (t = all_threads; t != END_TSO_QUEUE; t = t->global_link) {
+
+       while (t->what_next == ThreadRelocated) {
+           t = t->link;
+           ASSERT(get_itbl(t)->type == TSO);
+       }
+      
+       if (t->why_blocked != BlockedOnBlackHole) {
+           continue;
+       }
+
+       blocked_on = t->block_info.closure;
+
+       for (frame = t->su; ; frame = frame->link) {
+           switch (get_itbl(frame)->type) {
+
+           case UPDATE_FRAME:
+               if (frame->updatee == blocked_on) {
+                   /* We are blocking on one of our own computations, so
+                    * send this thread the NonTermination exception.  
+                    */
+                   IF_DEBUG(scheduler, 
+                            sched_belch("thread %d is blocked on itself", t->id));
+                   raiseAsync(t, (StgClosure *)NonTermination_closure);
+                   goto done;
+               }
+               else {
+                   continue;
+               }
+
+           case CATCH_FRAME:
+           case SEQ_FRAME:
+               continue;
+               
+           case STOP_FRAME:
+               break;
+           }
+           break;
+       }
+
+    done: ;
+    }   
+}
+
+//@node Debugging Routines, Index, Exception Handling Routines, Main scheduling code
+//@subsection Debugging Routines
+
+/* -----------------------------------------------------------------------------
+   Debugging: why is a thread blocked
+   -------------------------------------------------------------------------- */
+
+#ifdef DEBUG
+
+void
+printThreadBlockage(StgTSO *tso)
+{
+  switch (tso->why_blocked) {
+  case BlockedOnRead:
+    fprintf(stderr,"is blocked on read from fd %d", tso->block_info.fd);
+    break;
+  case BlockedOnWrite:
+    fprintf(stderr,"is blocked on write to fd %d", tso->block_info.fd);
+    break;
+  case BlockedOnDelay:
+    fprintf(stderr,"is blocked until %d", tso->block_info.target);
+    break;
+  case BlockedOnMVar:
+    fprintf(stderr,"is blocked on an MVar");
+    break;
+  case BlockedOnException:
+    fprintf(stderr,"is blocked on delivering an exception to thread %d",
+           tso->block_info.tso->id);
+    break;
+  case BlockedOnBlackHole:
+    fprintf(stderr,"is blocked on a black hole");
+    break;
+  case NotBlocked:
+    fprintf(stderr,"is not blocked");
+    break;
+#if defined(PAR)
+  case BlockedOnGA:
+    fprintf(stderr,"is blocked on global address; local FM_BQ is %p (%s)",
+           tso->block_info.closure, info_type(tso->block_info.closure));
+    break;
+  case BlockedOnGA_NoSend:
+    fprintf(stderr,"is blocked on global address (no send); local FM_BQ is %p (%s)",
+           tso->block_info.closure, info_type(tso->block_info.closure));
+    break;
+#endif
+  default:
+    barf("printThreadBlockage: strange tso->why_blocked: %d for TSO %d (%d)",
+        tso->why_blocked, tso->id, tso);
+  }
+}
+
+void
+printThreadStatus(StgTSO *tso)
+{
+  switch (tso->what_next) {
+  case ThreadKilled:
+    fprintf(stderr,"has been killed");
+    break;
+  case ThreadComplete:
+    fprintf(stderr,"has completed");
+    break;
+  default:
+    printThreadBlockage(tso);
+  }
+}
+
+void
+printAllThreads(void)
+{
+  StgTSO *t;
+
+# if defined(GRAN)
+  char time_string[TIME_STR_LEN], node_str[NODE_STR_LEN];
+  ullong_format_string(TIME_ON_PROC(CurrentProc), 
+                      time_string, rtsFalse/*no commas!*/);
+
+  sched_belch("all threads at [%s]:", time_string);
+# elif defined(PAR)
+  char time_string[TIME_STR_LEN], node_str[NODE_STR_LEN];
+  ullong_format_string(CURRENT_TIME,
+                      time_string, rtsFalse/*no commas!*/);
+
+  sched_belch("all threads at [%s]:", time_string);
+# else
+  sched_belch("all threads:");
+# endif
+
+  for (t = all_threads; t != END_TSO_QUEUE; t = t->global_link) {
+    fprintf(stderr, "\tthread %d ", t->id);
+    printThreadStatus(t);
+    fprintf(stderr,"\n");
+  }
+}
+    
+/* 
+   Print a whole blocking queue attached to node (debugging only).
+*/
+//@cindex print_bq
+# if defined(PAR)
+void 
+print_bq (StgClosure *node)
+{
+  StgBlockingQueueElement *bqe;
+  StgTSO *tso;
+  rtsBool end;
+
+  fprintf(stderr,"## BQ of closure %p (%s): ",
+         node, info_type(node));
+
+  /* should cover all closures that may have a blocking queue */
+  ASSERT(get_itbl(node)->type == BLACKHOLE_BQ ||
+        get_itbl(node)->type == FETCH_ME_BQ ||
+        get_itbl(node)->type == RBH ||
+        get_itbl(node)->type == MVAR);
+    
+  ASSERT(node!=(StgClosure*)NULL);         // sanity check
+
+  print_bqe(((StgBlockingQueue*)node)->blocking_queue);
+}
+
+/* 
+   Print a whole blocking queue starting with the element bqe.
+*/
+void 
+print_bqe (StgBlockingQueueElement *bqe)
+{
+  rtsBool end;
+
+  /* 
+     NB: In a parallel setup a BQ of an RBH must end with an RBH_Save closure;
+  */
+  for (end = (bqe==END_BQ_QUEUE);
+       !end; // iterate until bqe points to a CONSTR
+       end = (get_itbl(bqe)->type == CONSTR) || (bqe->link==END_BQ_QUEUE), 
+       bqe = end ? END_BQ_QUEUE : bqe->link) {
+    ASSERT(bqe != END_BQ_QUEUE);                               // sanity check
+    ASSERT(bqe != (StgBlockingQueueElement *)NULL);            // sanity check
+    /* types of closures that may appear in a blocking queue */
+    ASSERT(get_itbl(bqe)->type == TSO ||           
+          get_itbl(bqe)->type == BLOCKED_FETCH || 
+          get_itbl(bqe)->type == CONSTR); 
+    /* only BQs of an RBH end with an RBH_Save closure */
+    //ASSERT(get_itbl(bqe)->type != CONSTR || get_itbl(node)->type == RBH);
+
+    switch (get_itbl(bqe)->type) {
+    case TSO:
+      fprintf(stderr," TSO %u (%x),",
+             ((StgTSO *)bqe)->id, ((StgTSO *)bqe));
+      break;
+    case BLOCKED_FETCH:
+      fprintf(stderr," BF (node=%p, ga=((%x, %d, %x)),",
+             ((StgBlockedFetch *)bqe)->node, 
+             ((StgBlockedFetch *)bqe)->ga.payload.gc.gtid,
+             ((StgBlockedFetch *)bqe)->ga.payload.gc.slot,
+             ((StgBlockedFetch *)bqe)->ga.weight);
+      break;
+    case CONSTR:
+      fprintf(stderr," %s (IP %p),",
+             (get_itbl(bqe) == &stg_RBH_Save_0_info ? "RBH_Save_0" :
+              get_itbl(bqe) == &stg_RBH_Save_1_info ? "RBH_Save_1" :
+              get_itbl(bqe) == &stg_RBH_Save_2_info ? "RBH_Save_2" :
+              "RBH_Save_?"), get_itbl(bqe));
+      break;
+    default:
+      barf("Unexpected closure type %s in blocking queue", // of %p (%s)",
+          info_type((StgClosure *)bqe)); // , node, info_type(node));
+      break;
+    }
+  } /* for */
+  fputc('\n', stderr);
+}
+# elif defined(GRAN)
+void 
+print_bq (StgClosure *node)
+{
+  StgBlockingQueueElement *bqe;
+  PEs node_loc, tso_loc;
+  rtsBool end;
+
+  /* should cover all closures that may have a blocking queue */
+  ASSERT(get_itbl(node)->type == BLACKHOLE_BQ ||
+        get_itbl(node)->type == FETCH_ME_BQ ||
+        get_itbl(node)->type == RBH);
+    
+  ASSERT(node!=(StgClosure*)NULL);         // sanity check
+  node_loc = where_is(node);
+
+  fprintf(stderr,"## BQ of closure %p (%s) on [PE %d]: ",
+         node, info_type(node), node_loc);
+
+  /* 
+     NB: In a parallel setup a BQ of an RBH must end with an RBH_Save closure;
+  */
+  for (bqe = ((StgBlockingQueue*)node)->blocking_queue, end = (bqe==END_BQ_QUEUE);
+       !end; // iterate until bqe points to a CONSTR
+       end = (get_itbl(bqe)->type == CONSTR) || (bqe->link==END_BQ_QUEUE), bqe = end ? END_BQ_QUEUE : bqe->link) {
+    ASSERT(bqe != END_BQ_QUEUE);             // sanity check
+    ASSERT(bqe != (StgBlockingQueueElement *)NULL);  // sanity check
+    /* types of closures that may appear in a blocking queue */
+    ASSERT(get_itbl(bqe)->type == TSO ||           
+          get_itbl(bqe)->type == CONSTR); 
+    /* only BQs of an RBH end with an RBH_Save closure */
+    ASSERT(get_itbl(bqe)->type != CONSTR || get_itbl(node)->type == RBH);
+
+    tso_loc = where_is((StgClosure *)bqe);
+    switch (get_itbl(bqe)->type) {
+    case TSO:
+      fprintf(stderr," TSO %d (%p) on [PE %d],",
+             ((StgTSO *)bqe)->id, (StgTSO *)bqe, tso_loc);
+      break;
+    case CONSTR:
+      fprintf(stderr," %s (IP %p),",
+             (get_itbl(bqe) == &stg_RBH_Save_0_info ? "RBH_Save_0" :
+              get_itbl(bqe) == &stg_RBH_Save_1_info ? "RBH_Save_1" :
+              get_itbl(bqe) == &stg_RBH_Save_2_info ? "RBH_Save_2" :
+              "RBH_Save_?"), get_itbl(bqe));
+      break;
+    default:
+      barf("Unexpected closure type %s in blocking queue of %p (%s)",
+          info_type((StgClosure *)bqe), node, info_type(node));
+      break;
+    }
+  } /* for */
+  fputc('\n', stderr);
+}
+#else
+/* 
+   Nice and easy: only TSOs on the blocking queue
+*/
+void 
+print_bq (StgClosure *node)
+{
+  StgTSO *tso;
+
+  ASSERT(node!=(StgClosure*)NULL);         // sanity check
+  for (tso = ((StgBlockingQueue*)node)->blocking_queue;
+       tso != END_TSO_QUEUE; 
+       tso=tso->link) {
+    ASSERT(tso!=NULL && tso!=END_TSO_QUEUE);   // sanity check
+    ASSERT(get_itbl(tso)->type == TSO);  // guess what, sanity check
+    fprintf(stderr," TSO %d (%p),", tso->id, tso);
+  }
+  fputc('\n', stderr);
+}
+# endif
+
+#if defined(PAR)
+static nat
+run_queue_len(void)
+{
+  nat i;
+  StgTSO *tso;
+
+  for (i=0, tso=run_queue_hd; 
+       tso != END_TSO_QUEUE;
+       i++, tso=tso->link)
+    /* nothing */
+
+  return i;
+}
+#endif
+
+static void
+sched_belch(char *s, ...)
+{
+  va_list ap;
+  va_start(ap,s);
+#ifdef SMP
+  fprintf(stderr, "scheduler (task %ld): ", pthread_self());
+#elif defined(PAR)
+  fprintf(stderr, "== ");
+#else
+  fprintf(stderr, "scheduler: ");
+#endif
+  vfprintf(stderr, s, ap);
+  fprintf(stderr, "\n");
+}
+
+#endif /* DEBUG */
+
+
+//@node Index,  , Debugging Routines, Main scheduling code
+//@subsection Index
+
+//@index
+//* MainRegTable::  @cindex\s-+MainRegTable
+//* StgMainThread::  @cindex\s-+StgMainThread
+//* awaken_blocked_queue::  @cindex\s-+awaken_blocked_queue
+//* blocked_queue_hd::  @cindex\s-+blocked_queue_hd
+//* blocked_queue_tl::  @cindex\s-+blocked_queue_tl
+//* context_switch::  @cindex\s-+context_switch
+//* createThread::  @cindex\s-+createThread
+//* free_capabilities::  @cindex\s-+free_capabilities
+//* gc_pending_cond::  @cindex\s-+gc_pending_cond
+//* initScheduler::  @cindex\s-+initScheduler
+//* interrupted::  @cindex\s-+interrupted
+//* n_free_capabilities::  @cindex\s-+n_free_capabilities
+//* next_thread_id::  @cindex\s-+next_thread_id
+//* print_bq::  @cindex\s-+print_bq
+//* run_queue_hd::  @cindex\s-+run_queue_hd
+//* run_queue_tl::  @cindex\s-+run_queue_tl
+//* sched_mutex::  @cindex\s-+sched_mutex
+//* schedule::  @cindex\s-+schedule
+//* take_off_run_queue::  @cindex\s-+take_off_run_queue
+//* task_ids::  @cindex\s-+task_ids
+//* term_mutex::  @cindex\s-+term_mutex
+//* thread_ready_cond::  @cindex\s-+thread_ready_cond
+//@end index