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From "Maxim Sidnin (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CURATOR-276) Downgrade pattern doesn't work with "Shared Reentrant Read Write Lock"
Date Wed, 04 Nov 2015 08:21:27 GMT
Maxim Sidnin created CURATOR-276:
------------------------------------

             Summary: Downgrade pattern doesn't work with "Shared Reentrant Read Write Lock"
                 Key: CURATOR-276
                 URL: https://issues.apache.org/jira/browse/CURATOR-276
             Project: Apache Curator
          Issue Type: Bug
          Components: Recipes
    Affects Versions: 2.9.1
         Environment: Windows 7
Java 1.7.0_60
ZooKeeper Server 3.4.6-1569965

            Reporter: Maxim Sidnin


*Issue:* Downgrade pattern doesn't block already existed WRITE lock waiters.

*Scenario:*
- First thread takes a WRITE lock and waits
- Second thread starts and it is trying to obtain a WRITE lock. It waits because the WRITE
lock is hold be first thread.
- First thread does downgrade:
-- Takes the READ lock
-- Releases the WRITE lock
(x) At this point the first thread still holds the READ lock but the second one will get the
WRITE lock. 

It is reproducible for:
- 2 threads use the same CuratorFramework instance
- 2 threads use the different sessions
- 2 separate JVMs

There is attached test class: DowngradeTest.java and zoo.cfg

(i) Quote from Shared Reentrant Read Write Lock description ([link:http://curator.apache.org/curator-recipes/shared-reentrant-read-write-lock.html]):
{code}
Lock Downgrading Re-entrancy also allows downgrading from the write lock to a read lock, by
acquiring the write lock, then the read lock and then releasing the write lock. However, upgrading
from a read lock to the write lock is not possible.
{code}



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