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https://issues.apache.org/jira/browse/YARN-2594?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14148665#comment-14148665
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zhihai xu commented on YARN-2594:
---------------------------------
The [ReentrantReadWriteLock |
http://tutorials.jenkov.com/java-util-concurrent/readwritelock.html]
implementation is
{code}
Read Lock If no threads have locked the ReadWriteLock for writing,
and no thread have requested a write lock (but not yet obtained it).
Thus, multiple threads can lock the lock for reading.
Write Lock If no threads are reading or writing.
Thus, only one thread at a time can lock the lock for writing
{code}
Base on the above information, the first three threads can cause a deadlock,
The readLock is firstly acquired by thread#1, then thread#3 is blocked for
writeLock, finally when Thread#2 try to acquire the readLock, thread#2 is also
blocked because thread#3 is requesting the writeLock before thread#2.
So this is not a bug in Java.
The following is the source code in ReentrantReadWriteLock.java:
{code}
static final class NonfairSync extends Sync {
private static final long serialVersionUID = -8159625535654395037L;
final boolean writerShouldBlock() {
return false; // writers can always barge
}
final boolean readerShouldBlock() {
/* As a heuristic to avoid indefinite writer starvation,
* block if the thread that momentarily appears to be head
* of queue, if one exists, is a waiting writer. This is
* only a probabilistic effect since a new reader will not
* block if there is a waiting writer behind other enabled
* readers that have not yet drained from the queue.
*/
return apparentlyFirstQueuedIsExclusive();
}
}
{code}
readerShouldBlock will check whether any threads request writeLock before it.
> Potential deadlock in RM when querying ApplicationResourceUsageReport
> ---------------------------------------------------------------------
>
> Key: YARN-2594
> URL: https://issues.apache.org/jira/browse/YARN-2594
> Project: Hadoop YARN
> Issue Type: Bug
> Components: resourcemanager
> Affects Versions: 2.6.0
> Reporter: Karam Singh
> Assignee: Wangda Tan
> Priority: Blocker
> Attachments: YARN-2594.patch
>
>
> ResoruceManager sometimes become un-responsive:
> There was in exception in ResourceManager log and contains only following
> type of messages:
> {code}
> 2014-09-19 19:13:45,241 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 53000
> 2014-09-19 19:30:26,312 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 54000
> 2014-09-19 19:47:07,351 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 55000
> 2014-09-19 20:03:48,460 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 56000
> 2014-09-19 20:20:29,542 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 57000
> 2014-09-19 20:37:10,635 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 58000
> 2014-09-19 20:53:51,722 INFO event.AsyncDispatcher
> (AsyncDispatcher.java:handle(232)) - Size of event-queue is 59000
> {code}
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