fix: reset kScheduleRemote when we pull the queue #311
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romange
commented
Sep 2, 2024
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romange
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kostasrim
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Sep 2, 2024
| @@ -253,10 +253,6 @@ void Scheduler::ScheduleFromRemote(FiberInterface* cntx) { | |||
| cntx->DEBUG_remote_epoch = remote_epoch_.fetch_add(1, memory_order_relaxed); | |||
| remote_ready_queue_.Push(cntx); | |||
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| // clear the bit after we pushed to the queue. | |||
| cntx->flags_.fetch_and(~FiberInterface::kScheduleRemote, memory_order_release); | |||
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I find it slightly confusing that if isScheduledRemotely() is true above we clear the bit here whereas for this case we clear the bit when we pop the item in from the remote queue in the remote scheduler. What I had in mind is to clear the bit here and on the remote scheduler side to place back the item at the back of the remote_queue. That way this flow still remains in control of unseting the bit.
IMO I don't see a clear benefit in my suggestion so your change should be good as well.
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chakaz
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Sep 4, 2024
Before, we reset kScheduleRemote bit right after we pushed into the remote queue. But if this thread is slow, it is possible that the notified fiber will wake up before we reset the bit, and then it will go sleeping again and then another notifier will try to awake it and will check fail at line scheduler.cc:238 when it checks that the bit is set. If we reset it upon waking up, the fiber will reset it before suspending, so this situation can not happen. In addition, we print the stacktrace when we reach unexpected state. Signed-off-by: Roman Gershman <romange@gmail.com>
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