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https://issues.apache.org/jira/browse/HADOOP-19712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18024107#comment-18024107
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ASF GitHub Bot commented on HADOOP-19712:
-----------------------------------------
steveloughran opened a new pull request, #8006:
URL: https://github.com/apache/hadoop/pull/8006
Reworked how entrySet() and values() work, using .forEach() iterators after
reviewing what ConcurrentHashMap does internally; it does a (safe) traverse.
Add EvaluatingStatisticsMap.forEach() implementation which maps the passed
in BiConsumer down to the evaluators.forEach, evaluating each value as it goes.
Use that in IOStatisticsBinding.snapshot() code.
Tests for all this.
### For code changes:
- [X] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [X] Object storage: have the integration tests been executed and the
endpoint declared according to the connector-specific documentation?
- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
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- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
> S3A: Deadlock observed in IOStatistics EvaluatingStatisticsMap.entryset()
> -------------------------------------------------------------------------
>
> Key: HADOOP-19712
> URL: https://issues.apache.org/jira/browse/HADOOP-19712
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs, fs/s3
> Affects Versions: 3.3.6, 3.4.2
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Major
>
> We have evidence that `IOStatisticsSupport.snapshotIOStatistics()` can hang,
> specifically on the statistics collected by an S3AInputStream, whose
> statistics are merged in to the FS stats in close();
> {code}
> jdk.internal.misc.Unsafe.park(Native Method)
> java.util.concurrent.locks.LockSupport.park(LockSupport.java:341)
> java.util.concurrent.ForkJoinTask.awaitDone(ForkJoinTask.java:468)
> java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:687)
> java.util.stream.ReduceOps$ReduceOp.evaluateParallel(ReduceOps.java:927)
> java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
> java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
> org.apache.hadoop.fs.statistics.impl.EvaluatingStatisticsMap.entrySet(EvaluatingStatisticsMap.java:166)
> java.util.Collections$UnmodifiableMap.entrySet(Collections.java:1529)
> org.apache.hadoop.fs.statistics.impl.IOStatisticsBinding.copyMap(IOStatisticsBinding.java:172)
> org.apache.hadoop.fs.statistics.impl.IOStatisticsBinding.snapshotMap(IOStatisticsBinding.java:216)
> org.apache.hadoop.fs.statistics.impl.IOStatisticsBinding.snapshotMap(IOStatisticsBinding.java:199)
> org.apache.hadoop.fs.statistics.IOStatisticsSnapshot.snapshot(IOStatisticsSnapshot.java:165)
> org.apache.hadoop.fs.statistics.IOStatisticsSnapshot.<init>(IOStatisticsSnapshot.java:125)
> org.apache.hadoop.fs.statistics.IOStatisticsSupport.snapshotIOStatistics(IOStatisticsSupport.java:49)
> {code}
> the code in question is calling `parallelStream()`, which uses a fixed pool
> of threads shared by all uses of the API
> {code}
> Set<Entry<String, E>> r = evalEntries.parallelStream().map((e) ->
> new EntryImpl<>(e.getKey(), e.getValue().apply(e.getKey())))
> .collect(Collectors.toSet());
> {code}
> Proposed:
> * move off parallelStream() to stream()
> * review code to if there is any other way this iteration can lead to a
> deadlock, e.g. the apply() calls.
> * could we do the merge more efficiently?
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