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Merged
vstinner merged 7 commits into from
Apr 29, 2019
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bpo-36475: Finalize PyEval_AcquireLock() and PyEval_AcquireThread() properly #12667

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Finalize PyEval_AcquireLock() and PyEval_AcquireThread() properly
nanjekyejoannah Apr 25, 2019
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Finalize PyEval_AcquireLock() and PyEval_AcquireThread() properly
nanjekyejoannah Apr 25, 2019
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nanjekyejoannah Apr 25, 2019
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Finalize PyEval_AcquireLock() and PyEval_AcquireThread() properly
nanjekyejoannah Apr 26, 2019
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Merge branch 'issue36475' of https://github.com/nanjekyejoannah/cpyth…
nanjekyejoannah Apr 26, 2019
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Finalize PyEval_AcquireLock() and PyEval_AcquireThread() properly
nanjekyejoannah Apr 26, 2019
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30 changes: 30 additions & 0 deletions Doc/c-api/init.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1080,9 +1080,27 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
*tstate*, which should not be *NULL*. The lock must have been created earlier.
If this thread already has the lock, deadlock ensues.

.. note::
Calling this function from a thread when the runtime is finalizing
will terminate the thread, even if the thread was not created by Python.
You can use :c:func:`_Py_IsFinalizing` or :func:`sys.is_finalizing` to
check if the interpreter is in process of being finalized before calling
this function to avoid unwanted termination.

.. versionchanged:: 3.8
Updated to be consistent with :c:func:`PyEval_RestoreThread`,
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`,
and terminate the current thread if called while the interpreter is finalizing.

:c:func:`PyEval_RestoreThread` is a higher-level function which is always
available (even when threads have not been initialized).

.. note::

@ncoghlan ncoghlan Apr 26, 2019

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Ended up with two copies of this note.

Calling this function from a thread when the runtime is finalizing
will terminate the thread, even if the thread was not created by Python.
You can use :c:func:`_Py_IsFinalizing` or :func:`sys.is_finalizing` to

@ncoghlan ncoghlan Apr 25, 2019

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@vstinner Are you aware of any particular reason for _Py_IsFinalizing being a nominally private API? If we're recommending that folks call it in the documentation, that's a pretty strong sign that it should really be public.

(That can be broken out to a separate issue, though - it doesn't need to be resolved here)

@vstinner vstinner Apr 25, 2019

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I don't know. Feel free to open an issue to propose to make it public if you want.

In my PR #12934, I modified the internal _Py_CURRENTLY_FINALIZING() macro to add a runtime parameter :-) (PR currently under review.)

check if the interpreter is in process of being finalized before calling
this function to avoid unwanted termination.

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.. c:function:: void PyEval_ReleaseThread(PyThreadState *tstate)

Expand All @@ -1106,6 +1124,18 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
:c:func:`PyEval_RestoreThread` or :c:func:`PyEval_AcquireThread`
instead.

.. note::
Calling this function from a thread when the runtime is finalizing
will terminate the thread, even if the thread was not created by Python.
You can use :c:func:`_Py_IsFinalizing` or :func:`sys.is_finalizing` to
check if the interpreter is in process of being finalized before calling
this function to avoid unwanted termination.

.. versionchanged:: 3.8
Updated to be consistent with :c:func:`PyEval_RestoreThread`,
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`,
and terminate the current thread if called while the interpreter is finalizing.


.. c:function:: void PyEval_ReleaseLock()

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7 changes: 7 additions & 0 deletions Doc/whatsnew/3.8.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -726,6 +726,13 @@ Changes in Python behavior
always use the ``sys.platform.startswith('aix')``.
(Contributed by M. Felt in :issue:`36588`.)

* :c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread` now
terminate the current thread if called while the interpreter is
finalizing, making them consistent with :c:func:`PyEval_RestoreThread`,
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`. If this
behaviour is not desired, guard the call by checking :c:func:`_Py_IsFinalizing`
or :c:func:`sys.is_finalizing`.

Changes in the Python API
-------------------------

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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-04-02-20-02-22.bpo-36475.CjRps3.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
:c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread` now
terminate the current thread if called while the interpreter is
finalizing, making them consistent with :c:func:`PyEval_RestoreThread`,
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`.
28 changes: 16 additions & 12 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,7 @@ static PyObject * special_lookup(PyObject *, _Py_Identifier *);
static int check_args_iterable(PyObject *func, PyObject *vararg);
static void format_kwargs_error(PyObject *func, PyObject *kwargs);
static void format_awaitable_error(PyTypeObject *, int);
static inline void exit_thread_if_finalizing(PyThreadState *);

#define NAME_ERROR_MSG \
"name '%.200s' is not defined"
Expand Down Expand Up @@ -210,6 +211,7 @@ PyEval_AcquireLock(void)
if (tstate == NULL)
Py_FatalError("PyEval_AcquireLock: current thread state is NULL");
take_gil(tstate);
exit_thread_if_finalizing(tstate);
}

void
Expand All @@ -230,6 +232,7 @@ PyEval_AcquireThread(PyThreadState *tstate)
/* Check someone has called PyEval_InitThreads() to create the lock */
assert(gil_created());
take_gil(tstate);
exit_thread_if_finalizing(tstate);
if (PyThreadState_Swap(tstate) != NULL)
Py_FatalError(
"PyEval_AcquireThread: non-NULL old thread state");
Expand Down Expand Up @@ -298,12 +301,7 @@ PyEval_RestoreThread(PyThreadState *tstate)

int err = errno;
take_gil(tstate);
/* _Py_Finalizing is protected by the GIL */
if (_Py_IsFinalizing() && !_Py_CURRENTLY_FINALIZING(tstate)) {
drop_gil(tstate);
PyThread_exit_thread();
Py_UNREACHABLE();
}
exit_thread_if_finalizing(tstate);
errno = err;

PyThreadState_Swap(tstate);
Expand Down Expand Up @@ -1083,12 +1081,7 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
take_gil(tstate);

/* Check if we should make a quick exit. */
if (_Py_IsFinalizing() &&
!_Py_CURRENTLY_FINALIZING(tstate))
{
drop_gil(tstate);
PyThread_exit_thread();
}
exit_thread_if_finalizing(tstate);

if (PyThreadState_Swap(tstate) != NULL)
Py_FatalError("ceval: orphan tstate");
Expand Down Expand Up @@ -5199,6 +5192,17 @@ format_awaitable_error(PyTypeObject *type, int prevopcode)
}
}

static inline void
exit_thread_if_finalizing(PyThreadState *tstate)
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{
/* _Py_Finalizing is protected by the GIL */
if (_Py_IsFinalizing() && !_Py_CURRENTLY_FINALIZING(tstate)) {
drop_gil(tstate);
PyThread_exit_thread();
Py_UNREACHABLE();
}
}

static PyObject *
unicode_concatenate(PyObject *v, PyObject *w,
PyFrameObject *f, const _Py_CODEUNIT *next_instr)
Expand Down