bpo-36051: drop GIL during large b''.join operations #17757
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Improve multi-threaded performance by dropping the GIL in the fast path of bytes.join. To avoid increasing overhead for small joins, it is only done if the output size exceeds a threshold.
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For now I've only made the change for the b''.join fast-path, but if there is agreement I could also add it to the general case (non-empty separator). I think the code is safe against another thread mutating the sequence while the GIL is dropped (because the setup code takes it own refs to all the items), but it would be good if someone could double-check it. |
The existing stress test is increased in size to exceed GIL_THRESHOLD, and a new stress test is added with an empty separator (since that is a separate code path).
The GIL is now also dropped in the code path with non-empty separator, but it is *not* dropped if any of the items is not a `bytes` object (see discussion in bpo-36051 for reasoning).
Benchmarking shows that for smaller thresholds the multi-threading performance tends to be worse, or at least not much better.
methane
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Jan 28, 2020
methane
reviewed
Jan 28, 2020
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| Drop the GIL during large ``bytes.join`` operations. | |||
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Add your name in ACKS (see https://devguide.python.org/pullrequest/#crediting),
and add "Patch by ...." here.
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I've already added myself to ACKS, but have now added "Patch by ...".
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I can not find "Bruce Merry" in ACKS.
https://github.com/python/cpython/blob/master/Misc/ACKS
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That's the master version of ACKS. I'm adding myself in this pull request: https://github.com/bmerry/cpython/blob/bpo-36051/Misc/ACKS#L1109
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shihai1991
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Jan 31, 2020
Improve multi-threaded performance by dropping the GIL in the fast path of bytes.join. To avoid increasing overhead for small joins, it is only done if the output size exceeds a threshold.
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Improve multi-threaded performance by dropping the GIL in the fast path
of bytes.join. To avoid increasing overhead for small joins, it is only
done if the output size exceeds a threshold.
https://bugs.python.org/issue36051