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https://issues.apache.org/jira/browse/SPARK-21425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16095678#comment-16095678
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Ryan Williams commented on SPARK-21425:
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[~zsxwing] yea, it's static accumulators, and seems to only be a problem in
"local" mode. I just updated [my comment
above|https://issues.apache.org/jira/browse/SPARK-21425?focusedCommentId=16090017&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16090017]
because I'd previously thought I'd been able to repro this in cluster mode,
but now looking back at what I tried, that's not the case afaict.
Small nit: I'm not sure what you mean by "local-cluster mode… will always be 0"
though… I definitely get nonzero results on the driver with master "local\[*\]".
Anyway, thanks for investigating.
> LongAccumulator, DoubleAccumulator not threadsafe
> -------------------------------------------------
>
> Key: SPARK-21425
> URL: https://issues.apache.org/jira/browse/SPARK-21425
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.2.0
> Reporter: Ryan Williams
> Priority: Minor
>
> [AccumulatorV2
> docs|https://github.com/apache/spark/blob/v2.2.0/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L42-L43]
> acknowledge that accumulators must be concurrent-read-safe, but afaict they
> must also be concurrent-write-safe.
> The same docs imply that {{Int}} and {{Long}} meet either/both of these
> criteria, when afaict they do not.
> Relatedly, the provided
> [LongAccumulator|https://github.com/apache/spark/blob/v2.2.0/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L291]
> and
> [DoubleAccumulator|https://github.com/apache/spark/blob/v2.2.0/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L370]
> are not thread-safe, and should be expected to behave undefinedly when
> multiple concurrent tasks on the same executor write to them.
> [Here is a repro repo|https://github.com/ryan-williams/spark-bugs/tree/accum]
> with some simple applications that demonstrate incorrect results from
> {{LongAccumulator}}'s.
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