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gh-137017: Fix Thread.is_alive() to only return False after the underlying OS thread exits #137315

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gh-137017: Fix Thread.is_alive() to only return False after the underlying OS thread exits #137315

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gh-137017: Ensure is_alive() remains True until the underlying OS thr…
Abdoulrasheed Aug 1, 2025
8c2b76e
Fix Sphinx formatting in NEWS entry
Abdoulrasheed Aug 2, 2025
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-08-01-23-11-25.gh-issue-137017.0yGcNc.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :obj:`threading.Thread.is_alive` to remain ``True`` until the underlying OS
thread is fully cleaned up. This avoids false negatives in edge cases
involving thread monitoring or premature :obj:`threading.Thread.is_alive` calls.
4 changes: 4 additions & 0 deletions Modules/_threadmodule.c
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Expand Up @@ -704,6 +704,10 @@ PyThreadHandleObject_is_done(PyObject *op, PyObject *Py_UNUSED(dummy))
{
PyThreadHandleObject *self = PyThreadHandleObject_CAST(op);
if (_PyEvent_IsSet(&self->handle->thread_is_exiting)) {
if (_PyOnceFlag_CallOnce(&self->handle->once, join_thread, self->handle) == -1) {
PyErr_SetString(PyExc_RuntimeError, "failed to join thread");
return NULL;
}
Py_RETURN_TRUE;
}
else {
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