+ errno = t->saved_errno;
+ cap->in_haskell = rtsTrue;
+
+ recent_activity = ACTIVITY_YES;
+
+ switch (prev_what_next) {
+
+ case ThreadKilled:
+ case ThreadComplete:
+ /* Thread already finished, return to scheduler. */
+ ret = ThreadFinished;
+ break;
+
+ case ThreadRunGHC:
+ {
+ StgRegTable *r;
+ r = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
+ cap = regTableToCapability(r);
+ ret = r->rRet;
+ break;
+ }
+
+ case ThreadInterpret:
+ cap = interpretBCO(cap);
+ ret = cap->r.rRet;
+ break;
+
+ default:
+ barf("schedule: invalid what_next field");
+ }
+
+ cap->in_haskell = rtsFalse;
+
+#ifdef SMP
+ // If ret is ThreadBlocked, and this Task is bound to the TSO that
+ // blocked, we are in limbo - the TSO is now owned by whatever it
+ // is blocked on, and may in fact already have been woken up,
+ // perhaps even on a different Capability. It may be the case
+ // that task->cap != cap. We better yield this Capability
+ // immediately and return to normaility.
+ if (ret == ThreadBlocked) continue;
+#endif
+
+ ASSERT(cap->running_task == task);
+ ASSERT(task->cap == cap);
+ ASSERT(myTask() == task);
+
+ // The TSO might have moved, eg. if it re-entered the RTS and a GC
+ // happened. So find the new location:
+ t = cap->r.rCurrentTSO;
+
+ // And save the current errno in this thread.
+ t->saved_errno = errno;
+
+ // ----------------------------------------------------------------------
+
+ // Costs for the scheduler are assigned to CCS_SYSTEM
+#if defined(PROFILING)
+ stopHeapProfTimer();
+ CCCS = CCS_SYSTEM;
+#endif
+
+ // We have run some Haskell code: there might be blackhole-blocked
+ // threads to wake up now.
+ // Lock-free test here should be ok, we're just setting a flag.
+ if ( blackhole_queue != END_TSO_QUEUE ) {
+ blackholes_need_checking = rtsTrue;
+ }
+
+#if defined(THREADED_RTS)
+ IF_DEBUG(scheduler,debugBelch("sched (task %p): ", (void *)(unsigned long)(unsigned int)osThreadId()););
+#elif !defined(GRAN) && !defined(PARALLEL_HASKELL)
+ IF_DEBUG(scheduler,debugBelch("sched: "););
+#endif
+
+ schedulePostRunThread();
+
+ ready_to_gc = rtsFalse;
+
+ switch (ret) {
+ case HeapOverflow:
+ ready_to_gc = scheduleHandleHeapOverflow(cap,t);
+ break;
+
+ case StackOverflow:
+ scheduleHandleStackOverflow(cap,task,t);
+ break;
+
+ case ThreadYielding:
+ if (scheduleHandleYield(cap, t, prev_what_next)) {
+ // shortcut for switching between compiler/interpreter:
+ goto run_thread;
+ }
+ break;
+
+ case ThreadBlocked:
+ scheduleHandleThreadBlocked(t);
+ break;
+
+ case ThreadFinished:
+ if (scheduleHandleThreadFinished(cap, task, t)) return cap;
+ break;
+
+ default:
+ barf("schedule: invalid thread return code %d", (int)ret);
+ }
+
+ if (scheduleDoHeapProfile(ready_to_gc)) { ready_to_gc = rtsFalse; }
+ if (ready_to_gc) { scheduleDoGC(cap,task,rtsFalse); }
+ } /* end of while() */
+
+ IF_PAR_DEBUG(verbose,
+ debugBelch("== Leaving schedule() after having received Finish\n"));
+}
+
+/* ----------------------------------------------------------------------------
+ * Setting up the scheduler loop
+ * ------------------------------------------------------------------------- */
+
+static void
+schedulePreLoop(void)
+{
+#if defined(GRAN)
+ /* 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);
+
+ IF_DEBUG(gran,
+ debugBelch("GRAN: Init CurrentTSO (in schedule) = %p\n",
+ CurrentTSO);
+ G_TSO(CurrentTSO, 5));
+
+ if (RtsFlags.GranFlags.Light) {
+ /* Save current time; GranSim Light only */
+ CurrentTSO->gran.clock = CurrentTime[CurrentProc];
+ }
+#endif
+}
+
+/* ----------------------------------------------------------------------------
+ * Start any pending signal handlers
+ * ------------------------------------------------------------------------- */
+
+static void
+scheduleStartSignalHandlers(void)
+{
+#if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
+ if (signals_pending()) { // safe outside the lock
+ startSignalHandlers();
+ }
+#endif
+}
+
+/* ----------------------------------------------------------------------------
+ * Check for blocked threads that can be woken up.
+ * ------------------------------------------------------------------------- */
+
+static void
+scheduleCheckBlockedThreads(Capability *cap USED_WHEN_NON_THREADED_RTS)
+{
+#if !defined(THREADED_RTS)
+ //
+ // 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.
+ //
+ if ( !emptyQueue(blocked_queue_hd) || !emptyQueue(sleeping_queue) )
+ {
+ awaitEvent( emptyRunQueue(cap) && !blackholes_need_checking );
+ }
+#endif
+}
+
+
+/* ----------------------------------------------------------------------------
+ * Check for threads blocked on BLACKHOLEs that can be woken up
+ * ------------------------------------------------------------------------- */
+static void
+scheduleCheckBlackHoles (Capability *cap)
+{
+ if ( blackholes_need_checking ) // check without the lock first
+ {
+ ACQUIRE_LOCK(&sched_mutex);
+ if ( blackholes_need_checking ) {
+ checkBlackHoles(cap);
+ blackholes_need_checking = rtsFalse;
+ }
+ RELEASE_LOCK(&sched_mutex);
+ }
+}
+
+/* ----------------------------------------------------------------------------
+ * Detect deadlock conditions and attempt to resolve them.
+ * ------------------------------------------------------------------------- */
+
+static void
+scheduleDetectDeadlock (Capability *cap, Task *task)
+{
+
+#if defined(PARALLEL_HASKELL)
+ // ToDo: add deadlock detection in GUM (similar to SMP) -- HWL
+ return;
+#endif
+
+ /*
+ * Detect deadlock: when we have no threads to run, there are no
+ * threads blocked, waiting for I/O, or sleeping, and all the
+ * other tasks are waiting for work, we must have a deadlock of
+ * some description.
+ */
+ if ( emptyThreadQueues(cap) )
+ {
+#if defined(THREADED_RTS)
+ /*
+ * In the threaded RTS, we only check for deadlock if there
+ * has been no activity in a complete timeslice. This means
+ * we won't eagerly start a full GC just because we don't have
+ * any threads to run currently.
+ */
+ if (recent_activity != ACTIVITY_INACTIVE) return;
+#endif
+
+ IF_DEBUG(scheduler, sched_belch("deadlocked, forcing major GC..."));
+
+ // Garbage collection can release some new threads due to
+ // either (a) finalizers or (b) threads resurrected because
+ // they are unreachable and will therefore be sent an
+ // exception. Any threads thus released will be immediately
+ // runnable.
+ scheduleDoGC( cap, task, rtsTrue/*force major GC*/ );
+ recent_activity = ACTIVITY_DONE_GC;
+
+ if ( !emptyRunQueue(cap) ) return;
+
+#if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
+ /* If we have user-installed signal handlers, then wait
+ * for signals to arrive rather then bombing out with a
+ * deadlock.
+ */
+ if ( anyUserHandlers() ) {
+ IF_DEBUG(scheduler,
+ sched_belch("still deadlocked, waiting for signals..."));
+
+ awaitUserSignals();
+
+ if (signals_pending()) {
+ startSignalHandlers();
+ }
+
+ // either we have threads to run, or we were interrupted:
+ ASSERT(!emptyRunQueue(cap) || interrupted);
+ }
+#endif
+
+#if !defined(THREADED_RTS)
+ /* Probably a real deadlock. Send the current main thread the
+ * Deadlock exception.
+ */
+ if (task->tso) {
+ switch (task->tso->why_blocked) {
+ case BlockedOnSTM:
+ case BlockedOnBlackHole:
+ case BlockedOnException:
+ case BlockedOnMVar:
+ raiseAsync(cap, task->tso, (StgClosure *)NonTermination_closure);
+ return;
+ default:
+ barf("deadlock: main thread blocked in a strange way");
+ }
+ }
+ return;
+#endif
+ }
+}
+
+/* ----------------------------------------------------------------------------
+ * Process an event (GRAN only)
+ * ------------------------------------------------------------------------- */
+
+#if defined(GRAN)
+static StgTSO *
+scheduleProcessEvent(rtsEvent *event)
+{
+ StgTSO *t;
+
+ if (RtsFlags.GranFlags.Light)
+ GranSimLight_enter_system(event, &ActiveTSO); // adjust ActiveTSO etc
+
+ /* 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, debugBelch("GRAN: switch by event-type\n"));