alex created CURATOR-621:
----------------------------
Summary: 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: Jordan Zimmerman
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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