Weston Pace created ARROW-12208:
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Summary: [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
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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