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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4829) Accumulators are not thread safe
Date Fri, 14 Oct 2016 13:49:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15575382#comment-15575382
] 

ASF GitHub Bot commented on FLINK-4829:
---------------------------------------

Github user zentol commented on the issue:

    https://github.com/apache/flink/pull/2634
  
    I don't think fixes the reported issue. The supplied stacktrace shows that the exception
is thrown in a TreeMap, in the AccRegistry we however only deal with HashMaps. The histograms
internally have a TreeMap however.


> Accumulators are not thread safe
> --------------------------------
>
>                 Key: FLINK-4829
>                 URL: https://issues.apache.org/jira/browse/FLINK-4829
>             Project: Flink
>          Issue Type: Bug
>          Components: Local Runtime
>    Affects Versions: 1.2.0
>            Reporter: Till Rohrmann
>            Assignee: Maximilian Michels
>             Fix For: 1.2.0
>
>
> Flink's {{Accumulators}} are not thread safe. With the introduction of live accumulator
snapshots which are sent to the {{JobManager}}, we've introduced a concurrent access to accumulators
without properly guard them against concurrent modifications. So if an accumulator snapshot
is taken for an accumulator which is at the same time modified, it can cause an {{ConcurrentModificationException}}
as it was reported by an user: 
> {code}
> WARN  org.apache.flink.runtime.accumulators.AccumulatorRegistry     - Failed to serialize
accumulators for task.
> java.util.ConcurrentModificationException
>         at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1211)
>         at java.util.TreeMap$EntryIterator.next(TreeMap.java:1247)
>         at java.util.TreeMap$EntryIterator.next(TreeMap.java:1242)
>         at java.util.TreeMap.writeObject(TreeMap.java:2436)
>         at sun.reflect.GeneratedMethodAccessor491.invoke(Unknown Source) 
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>         at java.lang.reflect.Method.invoke(Method.java:498)
>         at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028)
>         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
>         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
>         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
>         at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
>         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
>         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
>         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
>         at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
>         at java.util.HashMap.internalWriteEntries(HashMap.java:1785)
>         at java.util.HashMap.writeObject(HashMap.java:1362)
>         at sun.reflect.GeneratedMethodAccessor189.invoke(Unknown Source) 
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>         at java.lang.reflect.Method.invoke(Method.java:498)
>         at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028)
>         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
>         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
>         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
>         at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
>         at org.apache.flink.util.InstantiationUtil.serializeObject(InstantiationUtil.java:301)
>         at org.apache.flink.util.SerializedValue.<init>(SerializedValue.java:52)
>         at org.apache.flink.runtime.accumulators.AccumulatorSnapshot.<init>(AccumulatorSnapshot.java:58)
>         at org.apache.flink.runtime.accumulators.AccumulatorRegistry.getSnapshot(AccumulatorRegistry.java:75)
>         at org.apache.flink.runtime.taskmanager.TaskManager$$anonfun$sendHeartbeatToJobManager$2.apply(TaskManager.scala:1286)
> {code}



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