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fix a race in click.testing.StreamMixer's finalization, seen in a multi-threaded context #2991

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Merged
Rowlando13 merged 2 commits into from
Jul 22, 2025
Merged

fix a race in click.testing.StreamMixer's finalization, seen in a multi-threaded context #2991

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e37cad2
BUG/TST: fix a race in `click.testing.StreamMixer`'s finalization, se…
neutrinoceros Jul 4, 2025
4679b1c
TST: adjust tests
neutrinoceros Jul 4, 2025
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12 changes: 12 additions & 0 deletions src/click/testing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,18 @@ def __init__(self) -> None:
self.stdout: io.BytesIO = BytesIOCopy(copy_to=self.output)
self.stderr: io.BytesIO = BytesIOCopy(copy_to=self.output)

def __del__(self) -> None:
"""
Guarantee that embedded file-like objects are closed in a
predictable order, protecting against races between
self.output being closed and other streams being flushed on close

.. versionadded:: 8.2.2
"""
self.stderr.close()
self.stdout.close()
self.output.close()


class _NamedTextIOWrapper(io.TextIOWrapper):
def __init__(
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6 changes: 2 additions & 4 deletions tests/test_testing.py
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Expand Up @@ -448,8 +448,7 @@ def test_isolation_stderr_errors():

with runner.isolation() as (_, err, _):
click.echo("\udce2", err=True, nl=False)

assert err.getvalue() == b"\\udce2"
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@neutrinoceros neutrinoceros Jul 4, 2025 •
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With my patch, stream objects yielded from runner.isolation, including err, may be closed as the context manager exits, dereferencing (hence, allowing gc to collect) its internal StreamMixer reference. Comparable tests already do it this way, so I'm hoping that this change is acceptable.

assert err.getvalue() == b"\\udce2"


def test_isolation_flushes_unflushed_stderr():
Expand All @@ -460,8 +459,7 @@ def test_isolation_flushes_unflushed_stderr():

with runner.isolation() as (_, err, _):
click.echo("\udce2", err=True, nl=False)

assert err.getvalue() == b"\\udce2"
assert err.getvalue() == b"\\udce2"

@click.command()
def cli():
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