bpo-36051: drop GIL during large b''.join operations by bmerry · Pull Request #17757

bpo-36051: drop GIL during large b''.join operations by bmerry · Pull Request #17757 · python/cpython

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.

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.

shihai1991 pushed a commit to shihai1991/cpython that referenced this pull request

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.

This was referenced

Mar 6, 2026

copybara-service bot pushed a commit to grpc/grpc that referenced this pull request

Mar 23, 2026

Remove one of the GIL contention from the grpc python wrapper.

The python [releases the GIL](python/cpython#17757) while doing b"".join. This was one of the major GIL contention in the python wrapper.

Fixing this significantly reduces the GIL contention.

Closes #41812

COPYBARA_INTEGRATE_REVIEW=#41812 from googlyrahman:samplefix df4796a
PiperOrigin-RevId: 888241985

asheshvidyut pushed a commit to asheshvidyut/grpc that referenced this pull request

Mar 26, 2026

)

Remove one of the GIL contention from the grpc python wrapper.

The python [releases the GIL](python/cpython#17757) while doing b"".join. This was one of the major GIL contention in the python wrapper.

Fixing this significantly reduces the GIL contention.

Closes grpc#41812

COPYBARA_INTEGRATE_REVIEW=grpc#41812 from googlyrahman:samplefix df4796a
PiperOrigin-RevId: 888241985

asheshvidyut pushed a commit to asheshvidyut/grpc that referenced this pull request

Apr 8, 2026

)

Remove one of the GIL contention from the grpc python wrapper.

The python [releases the GIL](python/cpython#17757) while doing b"".join. This was one of the major GIL contention in the python wrapper.

Fixing this significantly reduces the GIL contention.

Closes grpc#41812

COPYBARA_INTEGRATE_REVIEW=grpc#41812 from googlyrahman:samplefix df4796a
PiperOrigin-RevId: 888241985