[jira] [Reopened] (CURATOR-621) InterProcessReadWriteLock allows the write lock to be taken when the read one is not released

["Zili Chen (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CURATOR-621?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zili Chen reopened CURATOR-621:
-------------------------------

> InterProcessReadWriteLock allows the write lock to be taken when the read one is not released
> ---------------------------------------------------------------------------------------------
>
>                 Key: CURATOR-621
>                 URL: https://issues.apache.org/jira/browse/CURATOR-621
>             Project: Apache Curator
>          Issue Type: Bug
>    Affects Versions: 5.1.0
>            Reporter: alex
>            Assignee: Kezhu Wang
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> Hi,
> I have the following piece of code
>  
> {code:java}
> 01. rwLock.readLock().acquire();
> 02.
> 03. if (data needs to be refreshed) {
> 04.  rwLock.readLock().release(); // releaseing read lock becore acquire write one
> 05.  rwLock.writeLock().acquire();
> 06.  if (data needs to be refreshed) { // check again
> 07.     try {
> 08.       // refresh data
> 09.       rwLock.readLock().acquire();
> 10.     } finally {
> 11.       rwLock.writeLock().release();
> 12.     }
> 13.  }
> 14.  try {
> 15.   // read data
> 16.  } finally {
> 17.      rwLock.readLock().release();
> 18.  }
> 19. }
> {code}
> this is the standard read/write lock syntax described here [https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/ReentrantReadWriteLock.html]
> I noticed that when 2 processes run that code, if they both try to execute
> {code:java}
> 05. rwLock.writeLock().acquire();
> {code}
> as expected only one goes through, but as soon the process that went through releases the write lock
> {code:java}
> 11. rwLock.writeLock().release();
> {code}
> then the other process is able to acquire it and goes to line 06! Even if the first process acquired a read lock just before:
> {code:java}
> 09. rwLock.readLock().acquire();
> {code}
> I tested the same code using 2 threads on the same jvm rather than 2 processes and behaves the same.
> Then I tested 2 threads using the non distributed ReentrantReadWriteLock provided with java, and that one behaves correctly not allowing the second thread to lock on the write lock until the first thread releases its read lock.
>  



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