[jira] [Comment Edited] (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=13901125#comment-13901125 ] 

Henry Saputra edited comment on GORA-228 at 2/14/14 8:24 PM:
-------------------------------------------------------------

I am having a concern about the patch.

In the patch we have this:
   public Result<K, T> execute(Query<K, T> query) {
     K startKey = query.getStartKey();
     K endKey = query.getEndKey();
     if(startKey == null) {
       startKey = (K) map.firstKey();
     }
     if(endKey == null) {
       endKey = (K) map.lastKey();
     }
 ....
     return new MemResult<K,T>(this, query, submap);
   }

Given that "map" is static then it will shared by many MemStore within a JVM. The Key may or may not be same types, which in this case, the code:
  startKey = (K) map.firstKey();
could throw exception for illegal casting.

Thoughts?


was (Author: hsaputra):
I am having a concern about the patch.

In the patch we have this:

+  @SuppressWarnings("unchecked")
   @Override
   public Result<K, T> execute(Query<K, T> query) {
     K startKey = query.getStartKey();
     K endKey = query.getEndKey();
     if(startKey == null) {
-      startKey = map.firstKey();
+      startKey = (K) map.firstKey();
     }
     if(endKey == null) {
-      endKey = map.lastKey();
+      endKey = (K) map.lastKey();
     }
 
     //check if query.fields is null
     query.setFields(getFieldsToQuery(query.getFields()));
 
-    NavigableMap<K, T> submap = map.subMap(startKey, true, endKey, true);
+    ConcurrentNavigableMap<K,T> submap = map.subMap(startKey, true, endKey, true);
 
     return new MemResult<K,T>(this, query, submap);
   }

Given that "map" is static then it will shared by many MemStore within a JVM. The Key may or may not be same types, which in this case, the code:
  startKey = (K) map.firstKey();
could throw exception for illegal cast.

Thoughts?

> 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
>            Assignee: Yasin Kılınç
>             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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