Fix race condition in wakeupThreadOnCapability() (#2574)

[ghc-hetmet.git] / rts / Schedule.c

diff --git a/rts/Schedule.c b/rts/Schedule.c
index 94aac6c..f8a8748 100644 (file)
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1405,7 +1405,8 @@ scheduleDoGC (Capability *cap, Task *task USED_IF_THREADS, rtsBool force_major)
     StgTSO *t;
     rtsBool heap_census;
 #ifdef THREADED_RTS
-    static volatile StgWord waiting_for_gc;
+    /* extern static volatile StgWord waiting_for_gc; 
+       lives inside capability.c */
     rtsBool was_waiting;
     nat i;
 #endif
@@ -1422,6 +1423,10 @@ scheduleDoGC (Capability *cap, Task *task USED_IF_THREADS, rtsBool force_major)
     // the other tasks to sleep and stay asleep.
     //
        
+    /*  Other capabilities are prevented from running yet more Haskell
+       threads if waiting_for_gc is set. Tested inside
+       yieldCapability() and releaseCapability() in Capability.c */
+
     was_waiting = cas(&waiting_for_gc, 0, 1);
     if (was_waiting) {
        do {
@@ -1866,7 +1871,7 @@ scheduleThreadOn(Capability *cap, StgWord cpu USED_IF_THREADS, StgTSO *tso)
     if (cpu == cap->no) {
        appendToRunQueue(cap,tso);
     } else {
-       migrateThreadToCapability_lock(&capabilities[cpu],tso);
+       wakeupThreadOnCapability(cap, &capabilities[cpu], tso);
     }
 #else
     appendToRunQueue(cap,tso);
@@ -2307,8 +2312,6 @@ checkBlackHoles (Capability *cap)
        if (type != BLACKHOLE && type != CAF_BLACKHOLE) {
            IF_DEBUG(sanity,checkTSO(t));
            t = unblockOne(cap, t);
-           // urk, the threads migrate to the current capability
-           // here, but we'd like to keep them on the original one.
            *prev = t;
            any_woke_up = rtsTrue;
        } else {