bq->link = owner->bq;
owner->bq = bq;
dirty_TSO(cap, owner); // we modified owner->bq
-
+
+ // If the owner of the blackhole is currently runnable, then
+ // bump it to the front of the run queue. This gives the
+ // blocked-on thread a little boost which should help unblock
+ // this thread, and may avoid a pile-up of other threads
+ // becoming blocked on the same BLACKHOLE (#3838).
+ //
+ // NB. we check to make sure that the owner is not the same as
+ // the current thread, since in that case it will not be on
+ // the run queue.
+ if (owner->why_blocked == NotBlocked && owner->id != msg->tso->id) {
+ removeFromRunQueue(cap, owner);
+ pushOnRunQueue(cap,owner);
+ }
+
// point to the BLOCKING_QUEUE from the BLACKHOLE
write_barrier(); // make the BQ visible
((StgInd*)bh)->indirectee = (StgClosure *)bq;
if (info == &stg_BLOCKING_QUEUE_CLEAN_info) {
bq->header.info = &stg_BLOCKING_QUEUE_DIRTY_info;
- recordClosureMutated(cap,bq);
+ recordClosureMutated(cap,(StgClosure*)bq);
}
debugTraceCap(DEBUG_sched, cap, "thread %d blocked on thread %d",
(lnat)msg->tso->id, (lnat)owner->id);
+ // See above, #3838
+ if (owner->why_blocked == NotBlocked && owner->id != msg->tso->id) {
+ removeFromRunQueue(cap, owner);
+ pushOnRunQueue(cap,owner);
+ }
+
return 1; // blocked
}