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https://issues.apache.org/jira/browse/GORA-228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13662442#comment-13662442
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Lewis John McGibbney commented on GORA-228:
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Hi Renato. No the issue (ConcurrentModificationException) has not been solved.
I think we may need synchronize modifications to the Map within Nutch or
alternatively within Gora (which would probably be preference in all honesty as
Nutch should not be able to directly access the data sturcture).
Regardless such functionality, it should certainlybe documented whenever the
TreeMap is used within MemStore.
I don't think this should be too hard for us to address.
RE: Running same tests against different datastores, I think that this should
be implemented within our own testing suite and we should not rely upon third
party applications to ensure that testing of concurrent modifications is OK
within Gora.
We should really simulate something like the
TestGoraStorage#testMultiProcess[0] in Gora. The test is pretty straightforward
but AFAIK, we have nothing for our current testing suite in Gora!!!
wdyt?
[0]
http://svn.apache.org/repos/asf/nutch/branches/2.x/src/test/org/apache/nutch/storage/TestGoraStorage.java
> 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
>
>
> 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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