Maxim Sidnin created CURATOR-276:
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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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