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bpo-39511: PyThreadState_Clear() calls on_delete (GH-18296)
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PyThreadState.on_delete is a callback used to notify Python when a
thread completes. _thread._set_sentinel() function creates a lock
which is released when the thread completes. It sets on_delete
callback to the internal release_sentinel() function. This lock is
known as Threading._tstate_lock in the threading module.

The release_sentinel() function uses the Python C API. The problem is
that on_delete is called late in the Python finalization, when the C
API is no longer fully working.

The PyThreadState_Clear() function now calls the
PyThreadState.on_delete callback. Previously, that happened in
PyThreadState_Delete().

The release_sentinel() function is now called when the C API is still
fully working.
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vstinner authored Feb 1, 2020
1 parent 7dc1401 commit 4d96b46
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Showing 3 changed files with 12 additions and 3 deletions.
4 changes: 4 additions & 0 deletions Doc/c-api/init.rst
Original file line number Diff line number Diff line change
Expand Up @@ -1048,6 +1048,10 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
Reset all information in a thread state object. The global interpreter lock
must be held.
.. versionchanged:: 3.9
This function now calls the :c:member:`PyThreadState.on_delete` callback.
Previously, that happened in :c:func:`PyThreadState_Delete`.
.. c:function:: void PyThreadState_Delete(PyThreadState *tstate)
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
The :c:func:`PyThreadState_Clear` function now calls the
:c:member:`PyThreadState.on_delete` callback. Previously, that happened in
:c:func:`PyThreadState_Delete`.
8 changes: 5 additions & 3 deletions Python/pystate.c
Original file line number Diff line number Diff line change
Expand Up @@ -806,6 +806,10 @@ PyThreadState_Clear(PyThreadState *tstate)
Py_CLEAR(tstate->async_gen_finalizer);

Py_CLEAR(tstate->context);

if (tstate->on_delete != NULL) {
tstate->on_delete(tstate->on_delete_data);
}
}


Expand All @@ -830,9 +834,7 @@ tstate_delete_common(PyThreadState *tstate,
if (tstate->next)
tstate->next->prev = tstate->prev;
HEAD_UNLOCK(runtime);
if (tstate->on_delete != NULL) {
tstate->on_delete(tstate->on_delete_data);
}

PyMem_RawFree(tstate);

if (gilstate->autoInterpreterState &&
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