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From "Maximilian Michels (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (FLINK-4829) Accumulators are not thread safe
Date Fri, 14 Oct 2016 10:09:20 GMT

     [ https://issues.apache.org/jira/browse/FLINK-4829?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Maximilian Michels reassigned FLINK-4829:
-----------------------------------------

    Assignee: Maximilian Michels

> 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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