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Date: Fri, 28 Aug 2015 20:13:46 +0000 (UTC)
From: "Lewis John McGibbney (JIRA)" <jira@apache.org>
To: dev@gora.apache.org
Message-ID: <JIRA.12648321.1368911886000.197841.1440792826216@Atlassian.JIRA>
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 <JIRA.12648321.1368911886778@arcas>
Subject: [jira] [Commented] (GORA-228)
 java.util.ConcurrentModificationException when using MemStore for
 concurrent tests
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    [ https://issues.apache.org/jira/browse/GORA-228?page=3Dcom.atlassian.j=
ira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D147204=
94#comment-14720494 ]=20

Lewis John McGibbney commented on GORA-228:
-------------------------------------------

Thank you [~icebergx5] and [~cguzel]

> java.util.ConcurrentModificationException when using MemStore for concurr=
ent tests
> -------------------------------------------------------------------------=
---------
>
>                 Key: GORA-228
>                 URL: https://issues.apache.org/jira/browse/GORA-228
>             Project: Apache Gora
>          Issue Type: Sub-task
>          Components: gora-core
>    Affects Versions: 0.3
>            Reporter: Lewis John McGibbney
>            Assignee: Yasin K=C4=B1l=C4=B1n=C3=A7
>             Fix For: 0.7
>
>         Attachments: GORA-228.patch, GORA-228v2.patch
>
>
> Finally, a multithreaded test in [3] fails with the following
> {code}
> java.util.ConcurrentModificationException
> =09at java.util.TreeMap$NavigableSubMap$SubMapIterator.nextEntry(TreeMap.=
java:1594)
> =09at java.util.TreeMap$NavigableSubMap$SubMapKeyIterator.next(TreeMap.ja=
va:1655)
> =09at org.apache.gora.memory.store.MemStore$MemResult.nextInner(MemStore.=
java:81)
> =09at org.apache.gora.query.impl.ResultBase.next(ResultBase.java:112)
> =09at org.apache.nutch.storage.TestGoraStorage.readWrite(TestGoraStorage.=
java:74)
> =09at org.apache.nutch.storage.TestGoraStorage.access$100(TestGoraStorage=
.java:41)
> =09at org.apache.nutch.storage.TestGoraStorage$1.call(TestGoraStorage.jav=
a:107)
> =09at org.apache.nutch.storage.TestGoraStorage$1.call(TestGoraStorage.jav=
a:102)
> =09at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
> =09at java.util.concurrent.FutureTask.run(FutureTask.java:166)
> =09at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecuto=
r.java:1110)
> =09at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecut=
or.java:603)
> =09at java.lang.Thread.run(Thread.java:722)
> {code}
> I believe that the final failure is due to to the use of TreeMap [5] as a=
 private object in MemStore. TreeMap implementations are not synchronized. =
If multiple threads access a map concurrently, and at least one of the thre=
ads modifies the map structurally, it must be synchronized externally. (A s=
tructural modification is any operation that adds or deletes one or more ma=
ppings; merely changing the value associated with an existing key is not a =
structural modification.) This is typically accomplished by synchronizing o=
n some object that naturally encapsulates the map. If no such object exists=
, the map should be "wrapped" using the Collections.synchronizedSortedMap m=
ethod. This is best done at creation time, to prevent accidental unsynchron=
ized access to the map e.g.
>    SortedMap m =3D Collections.synchronizedSortedMap(new TreeMap(...));
> N.B. The NOTE on TreeMap's come right from the Oracle JavaDoc.
> [3] http://svn.apache.org/viewvc/nutch/branches/2.x/src/test/org/apache/n=
utch/storage/TestGoraStorage.java?view=3Dmarkup
> [4] http://svn.apache.org/viewvc/nutch/branches/2.x/src/test/org/apache/n=
utch/util/AbstractNutchTest.java?view=3Dmarkup
> [5] http://docs.oracle.com/javase/6/docs/api/java/util/TreeMap.html


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