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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7160) Improve IdLock and remove its minor defects
Date Wed, 14 Nov 2012 08:56:12 GMT
Hiroshi Ikeda created HBASE-7160:
------------------------------------

             Summary: 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
            Priority: Minor


Combination of synchronizations and concurrent collections complicates the code, and it is
hard to trace the code and to confirm its correctness. We should recreate 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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