[jira] [Commented] (GORA-228) java.util.ConcurrentModificationException when using MemStore for concurrent tests

["Henry Saputra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GORA-228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13895654#comment-13895654 ] 

Henry Saputra commented on GORA-228:
------------------------------------

I think we could just deliver this fix so I could work adding tests for multi threaded.

+1 for commit.

Will add this to trunk if no more comment in 48 hours.

Thanks guys!

> java.util.ConcurrentModificationException when using MemStore for concurrent 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
>             Fix For: 0.4
>
>         Attachments: GORA-228.patch
>
>
> Finally, a multithreaded test in [3] fails with the following
> {code}
> java.util.ConcurrentModificationException
> 	at java.util.TreeMap$NavigableSubMap$SubMapIterator.nextEntry(TreeMap.java:1594)
> 	at java.util.TreeMap$NavigableSubMap$SubMapKeyIterator.next(TreeMap.java:1655)
> 	at org.apache.gora.memory.store.MemStore$MemResult.nextInner(MemStore.java:81)
> 	at org.apache.gora.query.impl.ResultBase.next(ResultBase.java:112)
> 	at org.apache.nutch.storage.TestGoraStorage.readWrite(TestGoraStorage.java:74)
> 	at org.apache.nutch.storage.TestGoraStorage.access$100(TestGoraStorage.java:41)
> 	at org.apache.nutch.storage.TestGoraStorage$1.call(TestGoraStorage.java:107)
> 	at org.apache.nutch.storage.TestGoraStorage$1.call(TestGoraStorage.java:102)
> 	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
> 	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
> 	at 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 threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with an existing key is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedSortedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map e.g.
>    SortedMap m = 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/nutch/storage/TestGoraStorage.java?view=markup
> [4] http://svn.apache.org/viewvc/nutch/branches/2.x/src/test/org/apache/nutch/util/AbstractNutchTest.java?view=markup
> [5] http://docs.oracle.com/javase/6/docs/api/java/util/TreeMap.html



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