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Posted to dev@clerezza.apache.org by "Reto Bachmann-Gmür (JIRA)" <ji...@apache.org> on 2011/06/15 10:16:47 UTC
[jira] [Commented] (CLEREZZA-557) Potential Deadlock in UnionLock
[ https://issues.apache.org/jira/browse/CLEREZZA-557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13049676#comment-13049676 ]
Reto Bachmann-Gmür commented on CLEREZZA-557:
---------------------------------------------
the proposed patch looks good, I guess this solves the issue.
> Potential Deadlock in UnionLock
> -------------------------------
>
> Key: CLEREZZA-557
> URL: https://issues.apache.org/jira/browse/CLEREZZA-557
> Project: Clerezza
> Issue Type: Bug
> Reporter: Tsuyoshi Ito
> Priority: Critical
>
> 2 Threads:
> Thread A and Thread B
> Thread A tries to set a writelock on UnionMGraph consisting of Graphs AG, BG, CG and DG (AG is write locked, BG, CG, DG should be readlocked). BG and CG was successfully readlocked by thread A but in the mean while Thread B tries to set a writelock on a UnionMGraph constisting of DG, AG and EG. Thread B was able to writelock DG but has to wait for the readlock on AG (is writelocked by thread A). thread A has to wait for the readlock on the graph DG => Deadlock
> I suggest to refactor lock in UnionLock as follows:
> @Override
> public void lock() {
> while(!tryLock()) {
> try {
> Thread.sleep(10);
> } catch (InterruptedException ex) {
>
> }
> }
> }
> instead of:
> @Override
> public void lock() {
> for(Lock lock : locks) {
> lock.lock();
> }
> }
> }
> I was able to reproduce it:
> ----------------------------------------------------
> http://tpf.localhost/content.graph
> Read-Lock count: 0
> Write-Locked: YES
> Has queued threads: YES
> Thread holding write-lock:
> java.lang.Throwable
> at java.lang.Thread.getStackTrace(Thread.java:1426)
> at org.apache.clerezza.rdf.core.access.debug.WriteLockDebug.lock(WriteLockDebug.java:55)
> at org.apache.clerezza.rdf.utils.UnionMGraph$UnionLock.lock(UnionMGraph.java:237)
> at org.clerezza.cms.utils.LockUtils.runLocked(LockUtils.java:66)
> at org.clerezza.app.conceptmanager.core.ConceptManager.getConcept(ConceptManager.java:169)
> at org.clerezza.app.conceptmanager.core.ConceptManager.storeConcept(ConceptManager.java:160)
> ......
> Queue length: 1
> Queued threads:
> 42java.lang.Throwable
> at sun.misc.Unsafe.park(Native Method)
> at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireShared(AbstractQueuedSynchronizer.java:877)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1197)
> at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:594)
> at org.apache.clerezza.rdf.core.access.debug.ReadLockDebug.lock(ReadLockDebug.java:44)
> at org.apache.clerezza.rdf.utils.UnionMGraph$UnionLock.lock(UnionMGraph.java:237)
> ----------------------------------------------------
> http://tpf.localhost/feed.graph
> Read-Lock count: 0
> Write-Locked: YES
> Has queued threads: YES
> Thread holding write-lock:
> java.lang.Throwable
> at java.lang.Thread.getStackTrace(Thread.java:1426)
> at org.apache.clerezza.rdf.core.access.debug.WriteLockDebug.lock(WriteLockDebug.java:55)
> at org.apache.clerezza.rdf.core.access.LockableMGraphWrapper.remove(LockableMGraphWrapper.java:176)
> at org.apache.clerezza.rdf.utils.GraphNode.deleteProperties(GraphNode.java:536)
> ....
> Queue length: 1
> Queued threads:
> 45java.lang.Throwable
> at sun.misc.Unsafe.park(Native Method)
> at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireShared(AbstractQueuedSynchronizer.java:877)
> at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1197)
> at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:594)
> at org.apache.clerezza.rdf.core.access.debug.ReadLockDebug.lock(ReadLockDebug.java:44)
> at org.apache.clerezza.rdf.utils.UnionMGraph$UnionLock.lock(UnionMGraph.java:237)
> at org.apache.clerezza.rdf.utils.UnionMGraph$UnionLock.lock(UnionMGraph.java:237)
> at org.clerezza.cms.utils.LockUtils.runLocked(LockUtils.java:66)
> at org.clerezza.app.conceptmanager.core.ConceptManager.getConcept(ConceptManager.java:169)
> at org.clerezza.app.conceptmanager.core.ConceptManager.storeConcept(ConceptManager.java:160)
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