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e597358779
gh-153056: Fix a data race compiling the string.Template pattern in free-threading builds (GH-153057)
* gh-153056: Fix a data race compiling the string.Template pattern in free-threading builds
Template compiles its substitution pattern lazily and caches it on the class. On the free-threaded build two concurrent first uses could race: a thread that observed the pattern another thread had just compiled would try to recompile it, and re.compile() rejects flags on an already-compiled pattern, raising a spurious ValueError. Return the already-compiled pattern instead.
As a side effect, a subclass that supplies an already-compiled pattern now works too; previously it raised the same ValueError at class definition.
* Trim test comments and NEWS wording
* Document that the pattern attribute accepts a string or a compiled regex
* Comment the three states of pattern and note the documented-behavior fix in NEWS
* Update Doc/library/string.rst
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(cherry picked from commit 45729033bf)
Co-authored-by: tonghuaroot (童话) <tonghuaroot@gmail.com>
Co-authored-by: Barry Warsaw <barry@python.org>
35 lines
1.1 KiB
Python
35 lines
1.1 KiB
Python
import string
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import unittest
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from string import Template
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from test.support import threading_helper
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@threading_helper.requires_working_threading()
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class TestTemplateCompileRace(unittest.TestCase):
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def test_concurrent_first_use(self):
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# Racing the lazy pattern compile must not raise a spurious ValueError
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# from recompiling an already-compiled pattern. A throwaway subclass,
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# re-armed to the sentinel each round, keeps string.Template unmutated
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# (subclasses precompile eagerly in __init_subclass__).
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uncompiled = string._TemplatePattern
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errors = []
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def use_template(cls):
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try:
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cls("$x and ${y}").substitute(x=1, y=2)
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except Exception as e:
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errors.append(e)
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for _ in range(20):
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class T(Template):
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pass
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T.pattern = uncompiled
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T.flags = None
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threading_helper.run_concurrently(use_template, nthreads=10, args=(T,))
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self.assertEqual(errors, [], msg=f"unexpected errors: {errors}")
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if __name__ == "__main__":
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unittest.main()
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