Weston Pace created ARROW-12161:
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Summary: [C++] Async streaming CSV reader deadlocking when being
run synchronously from datasets
Key: ARROW-12161
URL: https://issues.apache.org/jira/browse/ARROW-12161
Project: Apache Arrow
Issue Type: Improvement
Components: C++
Reporter: Weston Pace
Assignee: Weston Pace
ARROW-11887 added async to the streaming CSV reader. In order to keep
backwards compatibility the old sync API simply calls the async API and waits
for it to finish. However, that wait cannot happen safely in a "nested"
context (e.g. dataset reading).
For example, imagine two cores. The dataset read launches two CSV scans. Each
scan occupies a core waiting for a future. Those futures are being filled by
I/O threads. The I/O threads finish and go to transfer. The transfer cannot
happen because the CPU executor is filled.
This will be fixed as part of ARROW-7001 but that still some ways away. An
easier change might be to take some of the 7001 changes and include them as
part of the 11887 feature.
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