test: ignore Python 3.15 fork-with-threads DeprecationWarning in test_multiprocessing#4143
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d-v-b merged 2 commits intoJul 13, 2026
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…_multiprocessing Python 3.15 makes os.fork() emit a DeprecationWarning when the process has multiple threads (python/cpython#84559). zarr's sync event-loop thread is always running by the time test_multiprocessing forks, and the suite runs with filterwarnings = ["error"], so the fork parametrizations fail on 3.15. Fork-safety despite those threads is exactly what this test pins down (zarr registers an os.register_at_fork handler), so keep the coverage and ignore the warning with a targeted per-param filter. Fixes zarr-developers#4086 Assisted-by: ClaudeCode:claude-fable-5
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this is a minor change to our tests. self-merging. |
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I got claude to fix #4086 by selectively ignoring the warning, because forking with threads is safe for zarr-python due to our use of a fork handler, and we will keep testing against it until python fully drops support. Claude's text is below
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Fixes #4086
Python 3.15 makes os.fork() emit a DeprecationWarning when the process has multiple threads (python/cpython#84559). zarr's sync event-loop thread is always running by the time test_multiprocessing forks, and the suite runs with filterwarnings = ["error"], so the fork parametrizations fail on 3.15. Fork-safety despite those threads is exactly what this test pins down (zarr registers an os.register_at_fork handler), so keep the coverage and ignore the warning with a targeted per-param filter.
Fixes #4086
Assisted-by: ClaudeCode:claude-fable-5
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TODO
docs/user-guide/*.mdchanges/