Hiroshi Ikeda created HBASE-7160:
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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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