X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2FSchedule.c;h=66af8be7cb5b6e02c03700102d102cd10b639aa3;hb=cfdf2515dd5b491f8229d44b98fa33adeeac7e60;hp=43c9b2a02441498369622a371ee0d784f1cde555;hpb=53aa3da2f606dc2f7248e556152a5f04b95b2dbd;p=ghc-hetmet.git

diff --git a/rts/Schedule.c b/rts/Schedule.c
index 43c9b2a..66af8be 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1188,36 +1188,32 @@ scheduleHandleStackOverflow (Capability *cap, Task *task, StgTSO *t)
 static rtsBool
 scheduleHandleYield( Capability *cap, StgTSO *t, nat prev_what_next )
 {
-    // Reset the context switch flag.  We don't do this just before
-    // running the thread, because that would mean we would lose ticks
-    // during GC, which can lead to unfair scheduling (a thread hogs
-    // the CPU because the tick always arrives during GC).  This way
-    // penalises threads that do a lot of allocation, but that seems
-    // better than the alternative.
-    cap->context_switch = 0;
-    
     /* 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.
      */
-#ifdef DEBUG
-    if (t->what_next != prev_what_next) {
-	debugTrace(DEBUG_sched,
-		   "--<< thread %ld (%s) stopped to switch evaluators", 
-		   (long)t->id, what_next_strs[t->what_next]);
-    }
-#endif
-    
+
     ASSERT(t->_link == END_TSO_QUEUE);
     
     // Shortcut if we're just switching evaluators: don't bother
     // doing stack squeezing (which can be expensive), just run the
     // thread.
-    if (t->what_next != prev_what_next) {
+    if (cap->context_switch == 0 && t->what_next != prev_what_next) {
+	debugTrace(DEBUG_sched,
+		   "--<< thread %ld (%s) stopped to switch evaluators", 
+		   (long)t->id, what_next_strs[t->what_next]);
 	return rtsTrue;
     }
 
+    // Reset the context switch flag.  We don't do this just before
+    // running the thread, because that would mean we would lose ticks
+    // during GC, which can lead to unfair scheduling (a thread hogs
+    // the CPU because the tick always arrives during GC).  This way
+    // penalises threads that do a lot of allocation, but that seems
+    // better than the alternative.
+    cap->context_switch = 0;
+    
     IF_DEBUG(sanity,
 	     //debugBelch("&& Doing sanity check on yielding TSO %ld.", t->id);
 	     checkTSO(t));
@@ -1331,6 +1327,17 @@ scheduleHandleThreadFinished (Capability *cap STG_UNUSED, Task *task, StgTSO *t)
 #ifdef DEBUG
 	  removeThreadLabel((StgWord)task->tso->id);
 #endif
+
+          // We no longer consider this thread and task to be bound to
+          // each other.  The TSO lives on until it is GC'd, but the
+          // task is about to be released by the caller, and we don't
+          // want anyone following the pointer from the TSO to the
+          // defunct task (which might have already been
+          // re-used). This was a real bug: the GC updated
+          // tso->bound->tso which lead to a deadlock.
+          t->bound = NULL;
+          task->tso = NULL;
+
 	  return rtsTrue; // tells schedule() to return
       }
 
@@ -1940,6 +1947,7 @@ Capability *
 scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability *cap)
 {
     Task *task;
+    StgThreadID id;
 
     // We already created/initialised the Task
     task = cap->running_task;
@@ -1955,14 +1963,15 @@ scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability *cap)
 
     appendToRunQueue(cap,tso);
 
-    debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)tso->id);
+    id = tso->id;
+    debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)id);
 
     cap = schedule(cap,task);
 
     ASSERT(task->stat != NoStatus);
     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 
-    debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)task->tso->id);
+    debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)id);
     return cap;
 }
 
@@ -2092,7 +2101,8 @@ exitScheduler(
     if (sched_state < SCHED_SHUTTING_DOWN) {
 	sched_state = SCHED_INTERRUPTING;
         waitForReturnCapability(&task->cap,task);
-	scheduleDoGC(task->cap,task,rtsFalse);    
+	scheduleDoGC(task->cap,task,rtsFalse);
+        ASSERT(task->tso == NULL);
         releaseCapability(task->cap);
     }
     sched_state = SCHED_SHUTTING_DOWN;
@@ -2102,6 +2112,7 @@ exitScheduler(
 	nat i;
 	
 	for (i = 0; i < n_capabilities; i++) {
+            ASSERT(task->tso == NULL);
 	    shutdownCapability(&capabilities[i], task, wait_foreign);
 	}
     }