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https://issues.apache.org/jira/browse/JCR-2890?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12994359#comment-12994359
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Jukka Zitting commented on JCR-2890:
------------------------------------
Note that at least this specific deadlock scenario can not occur with the
FineGrainedISMLocking strategy, since it never blocks incoming readers when
there are writers waiting for the lock.
> Deadlock in acl.EntryCollector / ItemManager
> --------------------------------------------
>
> Key: JCR-2890
> URL: https://issues.apache.org/jira/browse/JCR-2890
> Project: Jackrabbit Content Repository
> Issue Type: Bug
> Components: jackrabbit-core
> Affects Versions: 2.2.4
> Reporter: Jukka Zitting
>
> Here's another three-way deadlock that we've encountered:
> * Thread A holds a downgraded SISM write lock and is about to start
> delivering observation events to synchronous listeners
> * Thread B wants to write something and blocks waiting for the SISM write
> lock (since A holds the lock)
> * Thread C wants to read something and blocks waiting for the SISM read lock
> (since B waits for the lock)
> Normally such a scenario is handled without any problems, but there's a
> problem if the session used by thread C has a synchronous observation
> listener that attempts to read something from the repository during event
> delivery. In this case the following can happen:
> * Thread C holds the ItemManager synchronization lock higher up in the call
> chain
> * Observation listener code called by thread A attempts to read something
> from the repository, and blocks trying to acquire the ItemManager
> synchronization lock (since C holds it)
> In principle such a scenario should never happen as an observation listener
> (much less a synchronous one) should never try to use the session that might
> already be in use by another thread.
> Unfortunately the EntryCollector class in
> o.a.j.core.security.authorization.acl does not follow this guideline, which
> leads to the deadlock as shown below:
> Thread A:
> "127.0.0.1 [1297191119365] POST /bin/wcmcommand HTTP/1.0" nid=1179
> state=BLOCKED
> - waiting on <0x11c329fd> (a org.apache.jackrabbit.core.ItemManager)
> - locked <0x11c329fd> (a org.apache.jackrabbit.core.ItemManager)
> owned by 127.0.0.1 [1297191138443] POST /bin/wcmcommand HTTP/1.0 id=67
> at org.apache.jackrabbit.core.ItemManager.getNode(ItemManager.java:653)
> at org.apache.jackrabbit.core.ItemManager.getNode(ItemManager.java:605)
> at org.apache.jackrabbit.core.SessionImpl.getNode(SessionImpl.java:1406)
> at
> org.apache.jackrabbit.core.security.authorization.acl.EntryCollector.onEvent(EntryCollector.java:253)
> at
> org.apache.jackrabbit.core.observation.EventConsumer.consumeEvents(EventConsumer.java:246)
> at
> org.apache.jackrabbit.core.observation.ObservationDispatcher.dispatchEvents(ObservationDispatcher.java:214)
> at
> org.apache.jackrabbit.core.observation.EventStateCollection.dispatch(EventStateCollection.java:475)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager$Update.end(SharedItemStateManager.java:786)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.update(SharedItemStateManager.java:1488)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.update(LocalItemStateManager.java:349)
> at
> org.apache.jackrabbit.core.state.XAItemStateManager.update(XAItemStateManager.java:354)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.update(LocalItemStateManager.java:324)
> at
> org.apache.jackrabbit.core.state.SessionItemStateManager.update(SessionItemStateManager.java:328)
> at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1141)
> at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:920)
> Thread B:
> "Thread-2438" nid=2582 state=WAITING
> - waiting on <0x166e790e> (a
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
> - locked <0x166e790e> (a
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
> at java.lang.Object.wait(Native Method)
> at java.lang.Object.wait(Object.java:485)
> at
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock.acquire(Unknown
> Source)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking$WriteLockImpl.<init>(DefaultISMLocking.java:76)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking$WriteLockImpl.<init>(DefaultISMLocking.java:70)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking.acquireWriteLock(DefaultISMLocking.java:64)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.acquireWriteLock(SharedItemStateManager.java:1808)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.access$200(SharedItemStateManager.java:112)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager$Update.begin(SharedItemStateManager.java:565)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.beginUpdate(SharedItemStateManager.java:1458)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.update(SharedItemStateManager.java:1488)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.update(LocalItemStateManager.java:349)
> at
> org.apache.jackrabbit.core.state.XAItemStateManager.update(XAItemStateManager.java:354)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.update(LocalItemStateManager.java:324)
> at
> org.apache.jackrabbit.core.state.SessionItemStateManager.update(SessionItemStateManager.java:328)
> at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1141)
> at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:920)
> Thread C:
> "127.0.0.1 [1297191138443] POST /bin/wcmcommand HTTP/1.0" nid=67 state=WAITING
> - waiting on <0xf820edb> (a
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$ReaderLock)
> - locked <0xf820edb> (a
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$ReaderLock)
> at java.lang.Object.wait(Native Method)
> at java.lang.Object.wait(Object.java:485)
> at
> EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$ReaderLock.acquire(Unknown
> Source)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking$ReadLockImpl.<init>(DefaultISMLocking.java:102)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking$ReadLockImpl.<init>(DefaultISMLocking.java:96)
> at
> org.apache.jackrabbit.core.state.DefaultISMLocking.acquireReadLock(DefaultISMLocking.java:53)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.acquireReadLock(SharedItemStateManager.java:1794)
> at
> org.apache.jackrabbit.core.state.SharedItemStateManager.getItemState(SharedItemStateManager.java:257)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.getNodeState(LocalItemStateManager.java:107)
> at
> org.apache.jackrabbit.core.state.LocalItemStateManager.getItemState(LocalItemStateManager.java:171)
> at
> org.apache.jackrabbit.core.state.SessionItemStateManager.getItemState(SessionItemStateManager.java:200)
> at
> org.apache.jackrabbit.core.ItemManager.getItemData(ItemManager.java:391)
> at org.apache.jackrabbit.core.ItemManager.getItem(ItemManager.java:337)
> at org.apache.jackrabbit.core.ItemManager.getItem(ItemManager.java:638)
> at
> org.apache.jackrabbit.core.security.authorization.acl.ACLProvider$AclPermissions.canRead(ACLProvider.java:507)
> - locked java.lang.Object@6ad9b475
> at
> org.apache.jackrabbit.core.security.DefaultAccessManager.canRead(DefaultAccessManager.java:251)
> at
> org.apache.jackrabbit.core.query.lucene.QueryResultImpl.isAccessGranted(QueryResultImpl.java:374)
> at
> org.apache.jackrabbit.core.query.lucene.QueryResultImpl.collectScoreNodes(QueryResultImpl.java:353)
> at
> org.apache.jackrabbit.core.query.lucene.QueryResultImpl.getResults(QueryResultImpl.java:310)
> at
> org.apache.jackrabbit.core.query.lucene.SingleColumnQueryResult.<init>(SingleColumnQueryResult.java:70)
> at
> org.apache.jackrabbit.core.query.lucene.QueryImpl.execute(QueryImpl.java:133)
> at org.apache.jackrabbit.core.query.QueryImpl.execute(QueryImpl.java:127)
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