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https://issues.apache.org/jira/browse/STORM-841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15262275#comment-15262275
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Robert Joseph Evans commented on STORM-841:
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When is it not thread safe any more?
I thought the only thing that made it not thread safe was the shuffle grouping,
which was fixed when the load aware shuffle grouping code went in.
https://github.com/apache/storm/blob/v1.0.1/storm-core/src/jvm/org/apache/storm/grouping/ShuffleGrouping.java#L61
that went into the 1.0 release STORM-162.
For 0.10 and 9.6 it is not thread safe but from 1.0 on-wards I think it is.
> Thread-safeness of OutputCollector has documented contrary to two official
> doc.
> -------------------------------------------------------------------------------
>
> Key: STORM-841
> URL: https://issues.apache.org/jira/browse/STORM-841
> Project: Apache Storm
> Issue Type: Documentation
> Components: documentation
> Affects Versions: 0.10.0, 1.0.0, 0.9.6, 2.0.0
> Reporter: Jungtaek Lim
> Assignee: Jungtaek Lim
> Priority: Critical
>
> There're some issues with documentation.
> http://storm.apache.org/documentation/Concepts.html says
> {quote}
> Its perfectly fine to launch new threads in bolts that do processing
> asynchronously. OutputCollector is thread-safe and can be called at any time.
> {quote}
> and http://storm.apache.org/documentation/Troubleshooting.html says
> {quote}
> This is caused by having multiple threads issue methods on the
> OutputCollector. All emits, acks, and fails must happen on the same thread.
> One subtle way this can happen is if you make a IBasicBolt that emits on a
> separate thread. IBasicBolt's automatically ack after execute is called, so
> this would cause multiple threads to use the OutputCollector leading to this
> exception. When using a basic bolt, all emits must happen in the same thread
> that runs execute.
> {quote}
> It is a contradiction, and at least for now OutputCollector is not
> thread-safe.
> https://www.mail-archive.com/dev@storm.incubator.apache.org/msg00939.html
> Since newbie of Storm users may think Concepts page as "should read and keep
> it mind", it is some kind of critical that that such important documentation
> page has wrong content.
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