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https://issues.apache.org/jira/browse/HBASE-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018784#comment-16018784
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Yu Li commented on HBASE-18085:
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bq. It will succeed if the lock is available even if other threads are waiting.
I guess this is discussing the case that there're both timed and untimed
tryLock, and some threads waiting with timed tryLock, but the lock might be
grabbed by the untimed tryLock when lock released?
Here the purpose is to prevent parallel purge and no fairness required (it
doesn't matter which threads performs the purge), and there's no timed tryLock
ongoing, agree?
> Prevent parallel purge in ObjectPool
> ------------------------------------
>
> Key: HBASE-18085
> URL: https://issues.apache.org/jira/browse/HBASE-18085
> Project: HBase
> Issue Type: Bug
> Reporter: Yu Li
> Assignee: Yu Li
> Attachments: e89l05465.st3.jstack, HBASE-18085.patch
>
>
> Parallel purge in ObjectPool is meaningless and will cause contention issue
> since {{ReferenceQueue#poll}} has synchronization (source code shown below)
> {code}
> public Reference<? extends T> poll() {
> if (head == null)
> return null;
> synchronized (lock) {
> return reallyPoll();
> }
> }
> {code}
> We observed threads blocking on the purge method while using offheap bucket
> cache, and we could easily reproduce this by testing the 100% cache hit case
> in bucket cache with enough reading threads.
> We propose to add a purgeLock and use tryLock to avoid parallel purge.
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