gh-140814: Fix freeze_support() setting start method as side effect #144608
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…fect freeze_support() called get_start_method() without allow_none=True, which locked in the default start method context. This caused a subsequent set_start_method() call to raise "context has already been set". Use allow_none=True and accept None as a matching value, since spawn.freeze_support() independently detects spawned child processes. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Test that freeze_support() does not lock in the default start method, which would prevent a subsequent set_start_method() call. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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needs backport to 3.13
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Summary
freeze_support()calledget_start_method()withoutallow_none=True, which locked in the default start method context as a side effect. This caused a subsequentset_start_method()call to raiseRuntimeError: context has already been set.allow_none=Trueand acceptNoneas a matching value, sincespawn.freeze_support()independently detects spawned child processes.sys.frozenfirst as the more likely short-circuit (almost alwaysFalse).