+/* -----------------------------------------------------------------------------
+ * Blackhole detection: if we reach a deadlock, test whether any
+ * threads are blocked on themselves. Any threads which are found to
+ * be self-blocked get sent a NonTermination exception.
+ *
+ * This is only done in a deadlock situation in order to avoid
+ * performance overhead in the normal case.
+ * -------------------------------------------------------------------------- */
+
+static void
+detectBlackHoles( void )
+{
+ StgTSO *t = all_threads;
+ StgUpdateFrame *frame;
+ StgClosure *blocked_on;
+
+ for (t = all_threads; t != END_TSO_QUEUE; t = t->global_link) {
+
+ if (t->why_blocked != BlockedOnBlackHole) {
+ continue;
+ }
+
+ blocked_on = t->block_info.closure;
+
+ for (frame = t->su; ; frame = frame->link) {
+ switch (get_itbl(frame)->type) {
+
+ case UPDATE_FRAME:
+ if (frame->updatee == blocked_on) {
+ /* We are blocking on one of our own computations, so
+ * send this thread the NonTermination exception.
+ */
+ IF_DEBUG(scheduler,
+ sched_belch("thread %d is blocked on itself", t->id));
+ raiseAsync(t, (StgClosure *)NonTermination_closure);
+ goto done;
+ }
+ else {
+ continue;
+ }
+
+ case CATCH_FRAME:
+ case SEQ_FRAME:
+ continue;
+
+ case STOP_FRAME:
+ break;
+ }
+ break;
+ }
+
+ done:
+ }
+}
+