check black holes before doing GC in scheduleDoHeapProfile()

fixes #687, see comment for details.

diff --git a/ghc/rts/Schedule.c b/ghc/rts/Schedule.c
index 6fa21b7..3f10e70 100644 (file)
--- a/ghc/rts/Schedule.c
+++ b/ghc/rts/Schedule.c
@@ -1869,8 +1869,19 @@ scheduleDoHeapProfile( rtsBool ready_to_gc STG_UNUSED )
     if (performHeapProfile ||
        (RtsFlags.ProfFlags.profileInterval==0 &&
         RtsFlags.ProfFlags.doHeapProfile && ready_to_gc)) {
+
+       // checking black holes is necessary before GC, otherwise
+       // there may be threads that are unreachable except by the
+       // blackhole queue, which the GC will consider to be
+       // deadlocked.
+       scheduleCheckBlackHoles(&MainCapability);
+
+       IF_DEBUG(scheduler, sched_belch("garbage collecting before heap census"));
        GarbageCollect(GetRoots, rtsTrue);
+
+       IF_DEBUG(scheduler, sched_belch("performing heap census"));
        heapCensus();
+
        performHeapProfile = rtsFalse;
        return rtsTrue;  // true <=> we already GC'd
     }