/* ---------------------------------------------------------------------------
- *
- * (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() */
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.
* 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.
- *
+ * thread_ready_cond is signalled whenever
+ * !noCapabilities && !EMPTY_RUN_QUEUE().
*/
Condition thread_ready_cond = INIT_COND_VAR;
* Task.startTask() uses its current value.
*/
nat rts_n_waiting_tasks = 0;
+
+static Condition *passTarget = NULL;
+static rtsBool passingCapability = rtsFalse;
#endif
-/* -----------------------------------------------------------------------------
+#if defined(SMP)
+/*
+ * Free capability list.
+ */
+Capability *free_capabilities;
+#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 || blackholes_need_checking || signals_pending())
+#else
+#define ANY_WORK_TO_DO() (!EMPTY_RUN_QUEUE() || interrupted || blackholes_need_checking)
+#endif
+
+/* ----------------------------------------------------------------------------
Initialisation
- -------------------------------------------------------------------------- */
-static
-void
+ ------------------------------------------------------------------------- */
+
+static void
initCapability( Capability *cap )
{
cap->f.stgGCEnter1 = (F_)__stg_gc_enter_1;
cap->f.stgGCFun = (F_)__stg_gc_fun;
}
+/* -----------------------------------------------------------------------------
+ * Function: initCapabilities_(nat)
+ *
+ * Purpose: upon startup, allocate and fill in table
+ * holding 'n' Capabilities. Only for SMP, since
+ * it is the only build that supports multiple
+ * capabilities within the RTS.
+ * -------------------------------------------------------------------------- */
#if defined(SMP)
-static void initCapabilities_(nat n);
-#endif
+static void
+initCapabilities_(nat n)
+{
+ nat i;
+ Capability *cap, *prev;
+ cap = NULL;
+ prev = NULL;
+ for (i = 0; i < n; i++) {
+ cap = stgMallocBytes(sizeof(Capability), "initCapabilities");
+ initCapability(cap);
+ cap->link = prev;
+ prev = cap;
+ }
+ free_capabilities = cap;
+ rts_n_free_capabilities = n;
+ IF_DEBUG(scheduler,
+ sched_belch("allocated %d capabilities", rts_n_free_capabilities));
+}
+#endif /* SMP */
-/*
+/* ---------------------------------------------------------------------------
* 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);
- rts_n_free_capabilities = 1;
#endif
- return;
+#if defined(RTS_SUPPORTS_THREADS)
+ initCondition(&returning_worker_cond);
+ initCondition(&thread_ready_cond);
+#endif
+
+ rts_n_free_capabilities = 1;
}
-#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
+/* ----------------------------------------------------------------------------
+ grabCapability( Capability** )
-/* -----------------------------------------------------------------------------
- Acquiring capabilities
- -------------------------------------------------------------------------- */
+ (only externally visible when !RTS_SUPPORTS_THREADS. In the
+ threaded RTS, clients must use waitFor*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)
+#if defined(RTS_SUPPORTS_THREADS)
+static
+#endif
+void
+grabCapability( Capability** cap )
{
-#ifdef RTS_SUPPORTS_THREADS
+#if defined(SMP)
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;
rts_n_free_capabilities--;
+#else
+# if defined(RTS_SUPPORTS_THREADS)
+ ASSERT(rts_n_free_capabilities == 1);
+ rts_n_free_capabilities = 0;
+# endif
+ *cap = &MainCapability;
+ handleSignalsInThisThread();
#endif
-#ifdef RTS_SUPPORTS_THREADS
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): got capability\n",
- osThreadId()));
+#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
+ * ------------------------------------------------------------------------- */
+
+void
+releaseCapability( Capability* cap UNUSED_IF_NOT_SMP )
+{
+ // Precondition: sched_mutex is held.
+#if defined(RTS_SUPPORTS_THREADS)
#if !defined(SMP)
- STG_UNUSED
+ ASSERT(rts_n_free_capabilities == 0);
#endif
-)
-{ // Precondition: sched_mutex must be held
-#if defined(RTS_SUPPORTS_THREADS)
-#ifndef SMP
- ASSERT(rts_n_free_capabilities == 0);
+#if defined(SMP)
+ cap->link = free_capabilities;
+ free_capabilities = cap;
#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.
- */
+ // 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);
+ 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);
+ }
#if defined(SMP)
- // SMP variant untested
- cap->link = returning_capabilities;
- returning_capabilities = cap;
+ rts_n_free_capabilities++;
#else
+ rts_n_free_capabilities = 1;
#endif
- rts_n_waiting_workers--;
- signalCondition(&returning_worker_cond);
- } else /*if ( !EMPTY_RUN_QUEUE() )*/ {
+ 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++;
+ rts_n_free_capabilities++;
#else
- rts_n_free_capabilities = 1;
-#endif
- /* Signal that a capability is available */
- signalCondition(&thread_ready_cond);
- }
+ rts_n_free_capabilities = 1;
#endif
-#ifdef RTS_SUPPORTS_THREADS
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): released capability\n",
- osThreadId()));
+ // 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;
+ 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 grabReturnCapability() (via Schedule.resumeThread())
* result of the external call back to the Haskell thread that
* made it.
*
- * Pre-condition: pMutex is held.
- * Post-condition: pMutex is still 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 (%p): returning, waiting for lock.\n", osThreadId()));
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker (%p): returning; workers waiting: %d\n",
- osThreadId(), rts_n_waiting_workers));
- if ( noCapabilities() ) {
- rts_n_waiting_workers++;
- wakeBlockedWorkerThread();
- context_switch = 1; // make sure it's our turn soon
- waitCondition(&returning_worker_cond, pMutex);
+ // 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;
+ *pCap = free_capabilities;
+ free_capabilities = (*pCap)->link;
+ ASSERT(pCap != NULL);
#else
- *pCap = &MainCapability;
- ASSERT(rts_n_free_capabilities == 0);
- handleSignalsInThisThread();
+ *pCap = &MainCapability;
+ ASSERT(rts_n_free_capabilities == 0);
#endif
- } else {
- grabCapability(pCap);
- }
- return;
+ handleSignalsInThisThread();
+ } 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*,Condition*)
- *
- * 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.
- * Immediately afterwards, it tries to reaquire the Capabilty
- * using waitForWorkCapability.
- *
- *
- * Pre-condition: pMutex is assumed held and the thread possesses
- * a Capability.
- * Post-condition: pMutex is held and the thread possesses
- * a Capability.
- */
void
-yieldToReturningWorker(Mutex* pMutex, Capability** pCap, Condition* pThreadCond)
+yieldCapability( Capability** pCap )
{
- if ( rts_n_waiting_workers > 0 ) {
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): giving up RTS token\n", osThreadId()));
- releaseCapability(*pCap);
- /* And wait for work */
- waitForWorkCapability(pMutex, pCap, pThreadCond);
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): got back RTS token (after yieldToReturningWorker)\n",
- osThreadId()));
- }
- 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: 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**, Condition*)
+/* ----------------------------------------------------------------------------
+ * waitForCapability( Mutex*, Capability**, Condition* )
*
* Purpose: wait for a Capability to become available. In
* the process of doing so, updates the number
* call is made.
* If pThreadCond is not NULL, a capability can be specifically
* passed to this thread using passCapability.
- *
- * Pre-condition: pMutex is held.
- * Post-condition: pMutex is held and *pCap is held by the current thread
- */
+ * ------------------------------------------------------------------------- */
-static Condition *passTarget = NULL;
-
-void
-waitForWorkCapability(Mutex* pMutex, Capability** pCap, Condition* pThreadCond)
+void
+waitForCapability( Mutex* pMutex, Capability** pCap, Condition* pThreadCond )
{
-#ifdef SMP
- #error SMP version not implemented
-#endif
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): wait for cap (cond: %p)\n",
- osThreadId(),pThreadCond));
- while ( noCapabilities() || (pThreadCond && passTarget != pThreadCond)
- || (!pThreadCond && passTarget)) {
- if(pThreadCond)
- {
- waitCondition(pThreadCond, pMutex);
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): get passed capability\n",
- osThreadId()));
- }
- else
- {
- rts_n_waiting_tasks++;
- waitCondition(&thread_ready_cond, pMutex);
- rts_n_waiting_tasks--;
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): get normal capability\n",
- osThreadId()));
+ // 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"));
+ }
}
- }
- passTarget = NULL;
- grabCapability(pCap);
- return;
+ passingCapability = rtsFalse;
+ grabCapability(pCap);
+
+ // Post-condition: pMutex is held and *pCap is held by the current thread
+ return;
}
-/*
- * Function: passCapability(Mutex*, Capability*, Condition*)
- *
- * Purpose: Let go of the capability and make sure the thread associated
- * with the Condition pTargetThreadCond gets it next.
- *
- * Pre-condition: pMutex is held and cap is held by the current thread
- * Post-condition: pMutex is held; cap will be grabbed by the "target"
- * thread when pMutex is released.
- */
+/* ----------------------------------------------------------------------------
+ passCapability, passCapabilityToWorker
+ ------------------------------------------------------------------------- */
void
-passCapability(Mutex* pMutex, Capability* cap, Condition *pTargetThreadCond)
+passCapability( Condition *pTargetThreadCond )
{
-#ifdef SMP
- #error SMP version not implemented
-#endif
- rts_n_free_capabilities = 1;
- signalCondition(pTargetThreadCond);
+ // Pre-condition: pMutex is held and cap is held by the current thread
+
passTarget = pTargetThreadCond;
- IF_DEBUG(scheduler,
- fprintf(stderr,"worker thread (%p): passCapability\n",
- osThreadId()));
+ 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 */
-#if defined(SMP)
-/*
- * Function: initCapabilities_(nat)
- *
- * Purpose: upon startup, allocate and fill in table
- * holding 'n' Capabilities. Only for SMP, since
- * it is the only build that supports multiple
- * capabilities within the RTS.
- */
-static void
-initCapabilities_(nat n)
+/* ----------------------------------------------------------------------------
+ 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 )
{
- nat i;
- Capability *cap, *prev;
- cap = NULL;
- prev = NULL;
- for (i = 0; i < n; i++) {
- cap = stgMallocBytes(sizeof(Capability), "initCapabilities");
- initCapability(cap);
- cap->link = prev;
- prev = cap;
- }
- free_capabilities = cap;
- rts_n_free_capabilities = n;
- returning_capabilities = NULL;
- IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n", n_free_capabilities););
+#if defined(RTS_SUPPORTS_THREADS)
+ if ( !noCapabilities() && ANY_WORK_TO_DO() && rts_n_waiting_tasks > 0 ) {
+ signalCondition(&thread_ready_cond);
+ }
+ startSchedulerTaskIfNecessary();
+#endif
}
-#endif /* SMP */
+
+/* ----------------------------------------------------------------------------
+ prodWorker()
+
+ Wake up... time to die.
+ -------------------------------------------------------------------------- */
+void
+prodWorker ( void )
+{
+#if defined(RTS_SUPPORTS_THREADS)
+ signalCondition(&thread_ready_cond);
+#endif
+}
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