* --------------------------------------------------------------------------*/
#include "PosixSource.h"
#include "Rts.h"
-#include "Schedule.h"
#include "RtsUtils.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 */
* the task(s) that enter the Scheduler will check to see whether
* there are one or more worker threads blocked waiting on
* returning_worker_cond.
- *
- * Locks needed: sched_mutex
*/
nat rts_n_waiting_workers = 0;
+
+/* thread_ready_cond: when signalled, a thread has become runnable for a
+ * task to execute.
+ *
+ * In the non-SMP case, it also implies that the thread that is woken up has
+ * 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 noCapabilities doesn't hold.
+ *
+ */
+Condition thread_ready_cond = INIT_COND_VAR;
+
+/*
+ * To be able to make an informed decision about whether or not
+ * to create a new task when making an external call, keep track of
+ * the number of tasks currently blocked waiting on thread_ready_cond.
+ * (if > 0 => no need for a new task, just unblock an existing one).
+ *
+ * waitForWorkCapability() takes care of keeping it up-to-date;
+ * Task.startTask() uses its current value.
+ */
+nat rts_n_waiting_tasks = 0;
#endif
+/* -----------------------------------------------------------------------------
+ Initialisation
+ -------------------------------------------------------------------------- */
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)
{
#if defined(RTS_SUPPORTS_THREADS)
initCondition(&returning_worker_cond);
+ initCondition(&thread_ready_cond);
#endif
#if defined(SMP)
return;
}
-/* Free capability list.
- * Locks required: sched_mutex.
- */
#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
+ -------------------------------------------------------------------------- */
+
/*
* Function: grabCapability(Capability**)
*
* 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
- * through the use of the sched_mutex lock along with
- * condition variables thread_ready_cond and
+ * via the condition variables thread_ready_cond and
* returning_worker_cond.
*
- * Pre-condition: sched_mutex is held (in threaded builds only).
- *
*/
void grabCapability(Capability** cap)
{
+#ifdef RTS_SUPPORTS_THREADS
+ ASSERT(rts_n_free_capabilities > 0);
+#endif
#if !defined(SMP)
rts_n_free_capabilities = 0;
*cap = &MainCapability;
+ handleSignalsInThisThread();
#else
*cap = free_capabilities;
free_capabilities = (*cap)->link;
/*
* Function: releaseCapability(Capability*)
*
- * Purpose: Letting go of a capability.
+ * Purpose: Letting go of a capability. Causes a
+ * 'returning worker' thread or a 'waiting worker'
+ * to wake up, in that order.
*
- * Pre-condition: sched_mutex is assumed held by current thread.
- * Post-condition:
*/
void releaseCapability(Capability* cap
#if !defined(SMP)
STG_UNUSED
#endif
)
-{
-#if defined(SMP)
- cap->link = free_capabilities;
- free_capabilities = cap;
- rts_n_free_capabilities++;
-#else
- rts_n_free_capabilities = 1;
-#endif
-
+{ // Precondition: sched_mutex must be 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) {
* thread that is yielding its capability will repeatedly
* signal returning_worker_cond.
*/
+#if defined(SMP)
+ // SMP variant untested
+ cap->link = returning_capabilities;
+ returning_capabilities = cap;
+#else
+#endif
rts_n_waiting_workers--;
signalCondition(&returning_worker_cond);
- } else if ( !EMPTY_RUN_QUEUE() ) {
- /* Signal that work is available */
+ } else /*if ( !EMPTY_RUN_QUEUE() )*/ {
+#if defined(SMP)
+ cap->link = free_capabilities;
+ free_capabilities = cap;
+ rts_n_free_capabilities++;
+#else
+ rts_n_free_capabilities = 1;
+#endif
+ /* Signal that a capability is available */
signalCondition(&thread_ready_cond);
}
#endif
- return;
+ return;
}
#if defined(RTS_SUPPORTS_THREADS)
* value of rts_n_waiting_workers. If > 0, the worker thread
* will yield its capability to let a returning worker thread
* proceed with returning its result -- this is done via
- * yieldCapability().
+ * yieldToReturningWorker().
* - the worker thread that yielded its capability then tries
* to re-grab a capability and re-enter the Scheduler.
*/
* Function: grabReturnCapability(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: sched_mutex isn't held.
- * Post-condition: sched_mutex is held and a capability has
+ * Pre-condition: pMutex is held.
+ * Post-condition: pMutex is still held and a capability has
* been assigned to the worker thread.
*/
void
-grabReturnCapability(Capability** pCap)
+grabReturnCapability(Mutex* pMutex, Capability** pCap)
{
IF_DEBUG(scheduler,
- fprintf(stderr,"worker (%ld): returning, waiting for sched. lock.\n", osThreadId()));
- ACQUIRE_LOCK(&sched_mutex);
- rts_n_waiting_workers++;
+ fprintf(stderr,"worker (%ld): returning, waiting for lock.\n", osThreadId()));
IF_DEBUG(scheduler,
fprintf(stderr,"worker (%ld): returning; workers waiting: %d\n",
osThreadId(), rts_n_waiting_workers));
- while ( noCapabilities() ) {
- waitCondition(&returning_worker_cond, &sched_mutex);
+ if ( noCapabilities() ) {
+ rts_n_waiting_workers++;
+ wakeBlockedWorkerThread();
+ 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);
}
-
- grabCapability(pCap);
return;
}
+
+/* -----------------------------------------------------------------------------
+ Yielding/waiting for capabilities
+ -------------------------------------------------------------------------- */
+
/*
- * Function: yieldCapability(Capability**)
+ * 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: sched_mutex is held and the thread possesses
+ * Pre-condition: pMutex is assumed held and the thread possesses
* a Capability.
- * Post-condition: sched_mutex isn't held and the Capability has
+ * Post-condition: pMutex is held and the Capability has
* been given back.
*/
void
-yieldCapability(Capability* cap)
+yieldToReturningWorker(Mutex* pMutex, Capability** pCap)
{
+ if ( rts_n_waiting_workers > 0 ) {
IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%ld): giving up RTS token\n", osThreadId()));
- releaseCapability(cap);
- RELEASE_LOCK(&sched_mutex);
- yieldThread();
- /* At this point, sched_mutex has been given up & we've
- * forced a thread context switch. Guaranteed to be
- * enough for the signalled worker thread to race
- * ahead?
- */
- return;
+ fprintf(stderr,"worker thread (%p): giving up RTS token\n", osThreadId()));
+ releaseCapability(*pCap);
+ /* And wait for work */
+ waitForWorkCapability(pMutex, pCap, rtsFalse);
+ IF_DEBUG(scheduler,
+ fprintf(stderr,"worker thread (%p): got back RTS token (after yieldToReturningWorker)\n",
+ osThreadId()));
+ }
+ return;
+}
+
+
+/*
+ * Function: waitForWorkCapability(Mutex*, Capability**, rtsBool)
+ *
+ * Purpose: wait for a Capability to become available. In
+ * the process of doing so, updates the number
+ * of tasks currently blocked waiting for a capability/more
+ * 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.
+ * Post-condition: pMutex is held and *pCap is held by the current thread
+ */
+void
+waitForWorkCapability(Mutex* pMutex, Capability** pCap, rtsBool runnable)
+{
+ while ( noCapabilities() || (runnable && EMPTY_RUN_QUEUE()) ) {
+ rts_n_waiting_tasks++;
+ waitCondition(&thread_ready_cond, pMutex);
+ rts_n_waiting_tasks--;
+ }
+ grabCapability(pCap);
+ return;
}
#endif /* RTS_SUPPORTS_THREADS */
* holding 'n' Capabilities. Only for SMP, since
* it is the only build that supports multiple
* capabilities within the RTS.
- *
- * Pre-condition: sched_mutex is held.
- *
*/
static void
initCapabilities_(nat n)
}
free_capabilities = cap;
rts_n_free_capabilities = n;
+ returning_capabilities = NULL;
IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n", n_free_capabilities););
}
#endif /* SMP */
projects / ghc-hetmet.git / blobdiff