[GitHub] [arrow] westonpace commented on pull request #13635: ARROW-11841: [R][C++] Allow cancelling long-running commands

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westonpace commented on PR #13635:
URL: https://github.com/apache/arrow/pull/13635#issuecomment-1193022124

   > The StopToken will only work if it is actually polled by the implementation. I'm not sure the dataset layer does that. @westonpace
   
   It does not.  The exec plan has its own cancellation method (StopProducing).  However, the scan node will need to connect StopProducing to the actual readers.  So I think this will result in the exec plan creating its own stop source which it uses to generate stop tokens for the file readers.  Then, when the user calls StopProducing, the exec plan will cancel the source.
   
   Potentially we could adjust the exec plan to also have a stop source, in a "query options" object or something like that, and then we could get rid of StopProducing (at least externally).  That would give a slightly more consistent overall API.


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