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https://issues.apache.org/jira/browse/ARROW-12208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17314907#comment-17314907
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Neal Richardson commented on ARROW-12208:
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Correct, we cannot release 4.0 with a broken RTools 3.5 build. But if necessary
we can conditionally disable features in it--we already do this for S3 support.
> [C++] Add the ability to run async tasks without using the CPU thread pool
> --------------------------------------------------------------------------
>
> Key: ARROW-12208
> URL: https://issues.apache.org/jira/browse/ARROW-12208
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Weston Pace
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> This is required allow Windows 32-bit RTools 3.5 builds avoid crashing as
> they don't seem to properly implement the `<threading>` header.
>
> However, it could be generally useful to anyone that wants to avoid thread
> creation.
>
> Currently, the asynchronous approaches introduce necessary threading. For
> example, even a simple call to check if the CSVFileFormat supports a file
> requires peeking the file and reading the first block. These I/O operations
> happen on the I/O pools and then are transferred to the CPU thread pool
> (which is NOT the same thing as the calling thread) meanwhile the calling
> thread is blocked waiting for results.
>
> This can be avoided by treating the calling thread as a single threaded
> thread pool and then using that as the CPU thread pool. This allows all CPU
> work to be done on the calling thread alone. This could also allow us to
> remove duplicate code paths (e.g. code paths that exist only to keep
> functions serial such as the serial CSV reader) in the future.
>
> This capability could be extended to include the I/O thread pool as well at
> some point in the future.
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