[issue37280] Use threadpool for reading from file for sendfile fallback mode

[Andrew Svetlov]

Change by Andrew Svetlov <andrew.svetlov at gmail.com>:


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keywords: +patch
pull_requests: +13934
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/14076

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37280>
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