Darrel Schneider created GEODE-9365:
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Summary: HARegionQueue over throttles when multiple threads
attempt concurrent adds
Key: GEODE-9365
URL: https://issues.apache.org/jira/browse/GEODE-9365
Project: Geode
Issue Type: Bug
Components: client queues
Reporter: Darrel Schneider
HARegionQueue.checkQueueSizeConstraint has some code that implements a
"throttle" on adds to a queue that is full. It is supposed to wait
"eventEnqueueWaitTime" before doing an add. But because this code does two
syncs (putGuard and permitMon) and only waits on one of them, it holds the
other sync for the duration of this threads throttle. Any other concurrent
thread trying to add to the queue gets stuck on the putGuard sync that is held
by the first thread that is doing the timed wait. So it ends up waiting
"eventEnqueueWaitTime" to acquire the first sync and then ends up waiting again
"eventEnqueueWaitTime" when it does its own timed wait. If you have 10
concurrent threads trying to add one of them will end up waiting 10 *
"eventEnqueueWaitTime".
A couple ideas of how to fix this. Get rid of the putGuard and just use
permitMon. Then as soon as the first thread goes into its timed wait another
thread is allowed to sync on permitMon. But if this is done then we need to
think carefully about the code inside this sync block since it can not be
executed while one or more other threads are waiting in permitMon.
The other solution would be to compute the elapsed time it took to get into the
first sync and subtract that from the time we wait on permitMon. This seems
like a simple solution but does introduce at least one call of get time (the
second call is only needed if the queue is full).
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