/* ---------------------------------------------------------------------------
- *
- * (c) The GHC Team, 2002
+ * (c) The GHC Team, 2003
*
* Capabilities
*
* one global capability, namely MainCapability.
*
* --------------------------------------------------------------------------*/
+
#include "PosixSource.h"
#include "Rts.h"
#include "RtsUtils.h"
+#include "RtsFlags.h"
#include "OSThreads.h"
#include "Capability.h"
#include "Schedule.h" /* to get at EMPTY_RUN_QUEUE() */
+#include "Signals.h" /* to get at handleSignalsInThisThread() */
#if !defined(SMP)
Capability MainCapability; /* for non-SMP, we have one global capability */
#endif
+#if defined(RTS_SUPPORTS_THREADS)
+
nat rts_n_free_capabilities;
-#if defined(RTS_SUPPORTS_THREADS)
/* returning_worker_cond: when a worker thread returns from executing an
* external call, it needs to wait for an RTS Capability before passing
* on the result of the call to the Haskell thread that made it.
* there are one or more worker threads blocked waiting on
* returning_worker_cond.
*/
-static nat rts_n_waiting_workers = 0;
+nat rts_n_waiting_workers = 0;
/* thread_ready_cond: when signalled, a thread has become runnable for a
* task to execute.
* exclusive access to the RTS and all its data structures (that are not
* locked by the Scheduler's mutex).
*
- * thread_ready_cond is signalled whenever COND_NO_THREADS_READY doesn't hold.
- *
+ * thread_ready_cond is signalled whenever
+ * !noCapabilities && !EMPTY_RUN_QUEUE().
*/
Condition thread_ready_cond = INIT_COND_VAR;
-#if 0
-/* For documentation purposes only */
-#define COND_NO_THREADS_READY() (noCapabilities() || EMPTY_RUN_QUEUE())
-#endif
/*
* To be able to make an informed decision about whether or not
* the number of tasks currently blocked waiting on thread_ready_cond.
* (if > 0 => no need for a new task, just unblock an existing one).
*
- * waitForWork() takes care of keeping it up-to-date; Task.startTask()
- * uses its current value.
+ * waitForWorkCapability() takes care of keeping it up-to-date;
+ * Task.startTask() uses its current value.
*/
nat rts_n_waiting_tasks = 0;
+
+static Condition *passTarget = NULL;
+static rtsBool passingCapability = rtsFalse;
#endif
-/* -----------------------------------------------------------------------------
+#ifdef SMP
+#define UNUSED_IF_NOT_SMP
+#else
+#define UNUSED_IF_NOT_SMP STG_UNUSED
+#endif
+
+#if defined(RTS_USER_SIGNALS)
+#define ANY_WORK_TO_DO() (!EMPTY_RUN_QUEUE() || interrupted || signals_pending())
+#else
+#define ANY_WORK_TO_DO() (!EMPTY_RUN_QUEUE() || interrupted)
+#endif
+
+/* ----------------------------------------------------------------------------
Initialisation
- -------------------------------------------------------------------------- */
-static
-void
+ ------------------------------------------------------------------------- */
+
+static void
initCapability( Capability *cap )
{
- cap->f.stgChk0 = (F_)__stg_chk_0;
- cap->f.stgChk1 = (F_)__stg_chk_1;
cap->f.stgGCEnter1 = (F_)__stg_gc_enter_1;
- cap->f.stgUpdatePAP = (F_)__stg_update_PAP;
+ cap->f.stgGCFun = (F_)__stg_gc_fun;
}
#if defined(SMP)
static void initCapabilities_(nat n);
#endif
-/*
+/* ---------------------------------------------------------------------------
* Function: initCapabilities()
*
* Purpose: set up the Capability handling. For the SMP build,
* we keep a table of them, the size of which is
* controlled by the user via the RTS flag RtsFlags.ParFlags.nNodes
*
- * Pre-conditions: no locks assumed held.
- */
+ * ------------------------------------------------------------------------- */
void
-initCapabilities()
+initCapabilities( void )
{
-#if defined(RTS_SUPPORTS_THREADS)
- initCondition(&returning_worker_cond);
- initCondition(&thread_ready_cond);
-#endif
-
#if defined(SMP)
initCapabilities_(RtsFlags.ParFlags.nNodes);
#else
initCapability(&MainCapability);
+#endif
+
+#if defined(RTS_SUPPORTS_THREADS)
+ initCondition(&returning_worker_cond);
+ initCondition(&thread_ready_cond);
rts_n_free_capabilities = 1;
#endif
#if defined(SMP)
/* Free capability list. */
static Capability *free_capabilities; /* Available capabilities for running threads */
+static Capability *returning_capabilities;
+ /* Capabilities being passed to returning worker threads */
#endif
-/* -----------------------------------------------------------------------------
- Acquiring capabilities
- -------------------------------------------------------------------------- */
+/* ----------------------------------------------------------------------------
+ grabCapability( Capability** )
-/*
- * Function: grabCapability(Capability**)
- *
- * Purpose: the act of grabbing a capability is easy; just
- * remove one from the free capabilities list (which
- * may just have one entry). In threaded builds, worker
- * threads are prevented from doing so willy-nilly
- * via the condition variables thread_ready_cond and
- * returning_worker_cond.
- *
- */
-void grabCapability(Capability** cap)
+ (only externally visible when !RTS_SUPPORTS_THREADS. In the
+ threaded RTS, clients must use waitFor*Capability()).
+ ------------------------------------------------------------------------- */
+
+#if defined(RTS_SUPPORTS_THREADS)
+static
+#endif
+void
+grabCapability( Capability** cap )
{
#if !defined(SMP)
+#if defined(RTS_SUPPORTS_THREADS)
+ ASSERT(rts_n_free_capabilities == 1);
rts_n_free_capabilities = 0;
+#endif
*cap = &MainCapability;
+ handleSignalsInThisThread();
#else
*cap = free_capabilities;
free_capabilities = (*cap)->link;
rts_n_free_capabilities--;
#endif
+#if defined(RTS_SUPPORTS_THREADS)
+ IF_DEBUG(scheduler, sched_belch("worker: got capability"));
+#endif
}
-/*
+/* ----------------------------------------------------------------------------
* Function: releaseCapability(Capability*)
*
* Purpose: Letting go of a capability. Causes a
* 'returning worker' thread or a 'waiting worker'
* to wake up, in that order.
- *
- */
-void releaseCapability(Capability* cap
-#if !defined(SMP)
- STG_UNUSED
-#endif
-)
+ * ------------------------------------------------------------------------- */
+
+void
+releaseCapability( Capability* cap UNUSED_IF_NOT_SMP )
{
+ // Precondition: sched_mutex is held.
+#if defined(RTS_SUPPORTS_THREADS)
+#ifndef SMP
+ ASSERT(rts_n_free_capabilities == 0);
+#endif
+ // Check to see whether a worker thread can be given
+ // the go-ahead to return the result of an external call..
+ if (rts_n_waiting_workers > 0) {
+ // Decrement the counter here to avoid livelock where the
+ // thread that is yielding its capability will repeatedly
+ // signal returning_worker_cond.
+
#if defined(SMP)
- cap->link = free_capabilities;
- free_capabilities = cap;
- rts_n_free_capabilities++;
-#else
- rts_n_free_capabilities = 1;
+ // SMP variant untested
+ cap->link = returning_capabilities;
+ returning_capabilities = cap;
#endif
-#if defined(RTS_SUPPORTS_THREADS)
- /* Check to see whether a worker thread can be given
- the go-ahead to return the result of an external call..*/
- if (rts_n_waiting_workers > 0) {
- /* Decrement the counter here to avoid livelock where the
- * thread that is yielding its capability will repeatedly
- * signal returning_worker_cond.
- */
- rts_n_waiting_workers--;
- signalCondition(&returning_worker_cond);
- } else if ( !EMPTY_RUN_QUEUE() ) {
- /* Signal that work is available */
- signalCondition(&thread_ready_cond);
- }
+ rts_n_waiting_workers--;
+ signalCondition(&returning_worker_cond);
+ IF_DEBUG(scheduler, sched_belch("worker: released capability to returning worker"));
+ } else if (passingCapability) {
+ if (passTarget == NULL) {
+ signalCondition(&thread_ready_cond);
+ startSchedulerTaskIfNecessary();
+ } else {
+ signalCondition(passTarget);
+ }
+ rts_n_free_capabilities = 1;
+ IF_DEBUG(scheduler, sched_belch("worker: released capability, passing it"));
+
+ } else {
+#if defined(SMP)
+ cap->link = free_capabilities;
+ free_capabilities = cap;
+ rts_n_free_capabilities++;
+#else
+ rts_n_free_capabilities = 1;
#endif
- return;
+ // Signal that a capability is available
+ if (rts_n_waiting_tasks > 0 && ANY_WORK_TO_DO()) {
+ signalCondition(&thread_ready_cond);
+ }
+ startSchedulerTaskIfNecessary();
+ IF_DEBUG(scheduler, sched_belch("worker: released capability"));
+ }
+#endif
+ return;
}
#if defined(RTS_SUPPORTS_THREADS)
* call, it needs to communicate the result back. This is done
* as follows:
*
- * - in resumeThread(), the thread calls grabReturnCapability().
- * - If no capabilities are readily available, grabReturnCapability()
+ * - in resumeThread(), the thread calls waitForReturnCapability().
+ * - If no capabilities are readily available, waitForReturnCapability()
* increments a counter rts_n_waiting_workers, and blocks
* waiting for the condition returning_worker_cond to become
* signalled.
* to re-grab a capability and re-enter the Scheduler.
*/
-/*
- * Function: grabReturnCapability(Capability**)
+/* ----------------------------------------------------------------------------
+ * waitForReturnCapability( Mutext *pMutex, Capability** )
*
* Purpose: when an OS thread returns from an external call,
- * it calls grabReturningCapability() (via Schedule.resumeThread())
+ * it calls grabReturnCapability() (via Schedule.resumeThread())
* to wait for permissions to enter the RTS & communicate the
- * result of the ext. call back to the Haskell thread that
+ * result of the external call back to the Haskell thread that
* made it.
*
- * Pre-condition: pMutex isn't held.
- * Post-condition: pMutex is held and a capability has
- * been assigned to the worker thread.
- */
+ * ------------------------------------------------------------------------- */
+
void
-grabReturnCapability(Mutex* pMutex, Capability** pCap)
+waitForReturnCapability( Mutex* pMutex, Capability** pCap )
{
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker (%ld): returning, waiting for lock.\n", osThreadId()));
- ACQUIRE_LOCK(pMutex);
- rts_n_waiting_workers++;
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker (%ld): returning; workers waiting: %d\n",
- osThreadId(), rts_n_waiting_workers));
- while ( noCapabilities() ) {
- waitCondition(&returning_worker_cond, pMutex);
- }
-
- grabCapability(pCap);
- return;
+ // Pre-condition: pMutex is held.
+
+ IF_DEBUG(scheduler,
+ sched_belch("worker: returning; workers waiting: %d",
+ rts_n_waiting_workers));
+
+ if ( noCapabilities() || passingCapability ) {
+ rts_n_waiting_workers++;
+ context_switch = 1; // make sure it's our turn soon
+ waitCondition(&returning_worker_cond, pMutex);
+#if defined(SMP)
+ *pCap = returning_capabilities;
+ returning_capabilities = (*pCap)->link;
+#else
+ *pCap = &MainCapability;
+ ASSERT(rts_n_free_capabilities == 0);
+ handleSignalsInThisThread();
+#endif
+ } else {
+ grabCapability(pCap);
+ }
+
+ // Post-condition: pMutex is held, pCap points to a capability
+ // which is now held by the current thread.
+ return;
}
-/* -----------------------------------------------------------------------------
- Yielding/waiting for capabilities
- -------------------------------------------------------------------------- */
+/* ----------------------------------------------------------------------------
+ * yieldCapability( Mutex* pMutex, Capability** pCap )
+ * ------------------------------------------------------------------------- */
-/*
- * Function: yieldToReturningWorker(Mutex*,Capability*)
- *
- * Purpose: when, upon entry to the Scheduler, an OS worker thread
- * spots that one or more threads are blocked waiting for
- * permission to return back their result, it gives up
- * its Capability.
- *
- * Pre-condition: pMutex is assumed held and the thread possesses
- * a Capability.
- * Post-condition: pMutex isn't held and the Capability has
- * been given back.
- */
void
-yieldToReturningWorker(Mutex* pMutex, Capability* cap)
+yieldCapability( Capability** pCap )
{
- if ( rts_n_waiting_workers > 0 && noCapabilities() ) {
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%ld): giving up RTS token\n", osThreadId()));
- releaseCapability(cap);
- RELEASE_LOCK(pMutex);
- yieldThread();
- /* At this point, pMutex has been given up & we've
- * forced a thread context switch. Guaranteed to be
- * enough for the signalled worker thread to race
- * ahead of us?
- */
-
- /* Re-grab the mutex */
- ACQUIRE_LOCK(pMutex);
- }
- return;
+ // Pre-condition: pMutex is assumed held, the current thread
+ // holds the capability pointed to by pCap.
+
+ if ( rts_n_waiting_workers > 0 || passingCapability || !ANY_WORK_TO_DO()) {
+ IF_DEBUG(scheduler,
+ if (rts_n_waiting_workers > 0) {
+ sched_belch("worker: giving up capability (returning wkr)");
+ } else if (passingCapability) {
+ sched_belch("worker: giving up capability (passing capability)");
+ } else {
+ sched_belch("worker: giving up capability (no threads to run)");
+ }
+ );
+ releaseCapability(*pCap);
+ *pCap = NULL;
+ }
+
+ // Post-condition: pMutex is assumed held, and either:
+ //
+ // 1. *pCap is NULL, in which case the current thread does not
+ // hold a capability now, or
+ // 2. *pCap is not NULL, in which case the current thread still
+ // holds the capability.
+ //
+ return;
}
-/*
- * Function: waitForWorkCapability(Mutex*, Capability**, rtsBool)
+/* ----------------------------------------------------------------------------
+ * waitForCapability( Mutex*, Capability**, Condition* )
*
* Purpose: wait for a Capability to become available. In
* the process of doing so, updates the number
* work. That counter is used when deciding whether or
* not to create a new worker thread when an external
* call is made.
- *
- * Pre-condition: pMutex is held.
- */
-void
-waitForWorkCapability(Mutex* pMutex, Capability** pCap, rtsBool runnable)
+ * If pThreadCond is not NULL, a capability can be specifically
+ * passed to this thread using passCapability.
+ * ------------------------------------------------------------------------- */
+
+void
+waitForCapability( Mutex* pMutex, Capability** pCap, Condition* pThreadCond )
{
- while ( noCapabilities() || (runnable && EMPTY_RUN_QUEUE()) ) {
- rts_n_waiting_tasks++;
- waitCondition(&thread_ready_cond, pMutex);
- rts_n_waiting_tasks--;
- }
- grabCapability(pCap);
- return;
+ // Pre-condition: pMutex is held.
+
+ while ( noCapabilities() ||
+ (passingCapability && passTarget != pThreadCond) ||
+ !ANY_WORK_TO_DO()) {
+ IF_DEBUG(scheduler,
+ sched_belch("worker: wait for capability (cond: %p)",
+ pThreadCond));
+
+ if (pThreadCond != NULL) {
+ waitCondition(pThreadCond, pMutex);
+ IF_DEBUG(scheduler, sched_belch("worker: get passed capability"));
+ } else {
+ rts_n_waiting_tasks++;
+ waitCondition(&thread_ready_cond, pMutex);
+ rts_n_waiting_tasks--;
+ IF_DEBUG(scheduler, sched_belch("worker: get normal capability"));
+ }
+ }
+ passingCapability = rtsFalse;
+ grabCapability(pCap);
+
+ // Post-condition: pMutex is held and *pCap is held by the current thread
+ return;
+}
+
+/* ----------------------------------------------------------------------------
+ passCapability, passCapabilityToWorker
+ ------------------------------------------------------------------------- */
+
+void
+passCapability( Condition *pTargetThreadCond )
+{
+ // Pre-condition: pMutex is held and cap is held by the current thread
+
+ passTarget = pTargetThreadCond;
+ passingCapability = rtsTrue;
+ IF_DEBUG(scheduler, sched_belch("worker: passCapability"));
+
+ // Post-condition: pMutex is held; cap is still held, but will be
+ // passed to the target thread when next released.
+}
+
+void
+passCapabilityToWorker( void )
+{
+ // Pre-condition: pMutex is held and cap is held by the current thread
+
+ passTarget = NULL;
+ passingCapability = rtsTrue;
+ IF_DEBUG(scheduler, sched_belch("worker: passCapabilityToWorker"));
+
+ // Post-condition: pMutex is held; cap is still held, but will be
+ // passed to a worker thread when next released.
}
+
#endif /* RTS_SUPPORTS_THREADS */
+/* ----------------------------------------------------------------------------
+ threadRunnable()
+
+ Signals that a thread has been placed on the run queue, so a worker
+ might need to be woken up to run it.
+
+ ToDo: should check whether the thread at the front of the queue is
+ bound, and if so wake up the appropriate worker.
+ -------------------------------------------------------------------------- */
+
+void
+threadRunnable ( void )
+{
+#if defined(RTS_SUPPORTS_THREADS)
+ if ( !noCapabilities && ANY_WORK_TO_DO() && rts_n_waiting_tasks > 0 ) {
+ signalCondition(&thread_ready_cond);
+ }
+ startSchedulerTaskIfNecessary();
+#endif
+}
+
+/* ------------------------------------------------------------------------- */
+
#if defined(SMP)
/*
* Function: initCapabilities_(nat)
}
free_capabilities = cap;
rts_n_free_capabilities = n;
- IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n", n_free_capabilities););
+ returning_capabilities = NULL;
+ IF_DEBUG(scheduler,
+ sched_belch("allocated %d capabilities", n_free_capabilities));
}
#endif /* SMP */
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