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https://issues.apache.org/jira/browse/HBASE-7160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13499994#comment-13499994
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Hiroshi Ikeda commented on HBASE-7160:
--------------------------------------
{quote}
Looking at Entry.release():
+ public void release() {
+ if (released.compareAndSet(false, true)) {
Would this do the trick ?
{quote}
Calling compareAndSet() in the Entry.release() is a mere safety net.
Otherwise multiple calling Entry.release() can break the exclusiveness of
IdLock.
> Improve IdLock and remove its minor defects
> -------------------------------------------
>
> Key: HBASE-7160
> URL: https://issues.apache.org/jira/browse/HBASE-7160
> Project: HBase
> Issue Type: Improvement
> Reporter: Hiroshi Ikeda
> Assignee: Hiroshi Ikeda
> Priority: Minor
> Attachments: HBASE-7160.patch
>
>
> Combination of synchronizations and concurrent collections complicates the
> code, and it is hard to trace the code and to confirm its correctness. We
> should re-create the class and make it more understandable.
> In the current code, I find the following minor defects:
> (1) In the case that there is a waiting thread for a lock in getLockEntry()
> and another thread is releasing the lock by calling releaseLockEntry(),
> trying to get the lock with a 3rd thread by calling getLockEntry() falls into
> a busy loop until the waiting thread wakes up and gets the lock.
> Even if notify() wakes up the blocked thread and causes a context switch to
> the waked thread immediately, synchronization might block the waked thread
> and cause another context switch, and the busy loop might continue for a
> while.
> (2) In the same case as (1), since releasing the lock is merely notifying
> without removing the lock-entry from the map, interrupting the waiting thread
> might leave an unused lock-entry (entry.numWaiters == 0) in the map. This is
> a memory leak unless the id of the lock is used again.
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