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bpo-39877: Refactor take_gil() function #18885

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Merged
merged 1 commit into from
Mar 9, 2020
Merged

bpo-39877: Refactor take_gil() function #18885

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78 changes: 13 additions & 65 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -198,16 +198,6 @@ ensure_tstate_not_null(const char *func, PyThreadState *tstate)
}


#ifndef NDEBUG
static int is_tstate_valid(PyThreadState *tstate)
{
assert(!_PyMem_IsPtrFreed(tstate));
assert(!_PyMem_IsPtrFreed(tstate->interp));
return 1;
}
#endif


int
PyEval_ThreadsInitialized(void)
{
Expand All @@ -230,13 +220,15 @@ _PyEval_InitThreads(PyThreadState *tstate)

PyThread_init_thread();
create_gil(gil);
take_gil(ceval, tstate);

take_gil(tstate);

struct _pending_calls *pending = &ceval->pending;
pending->lock = PyThread_allocate_lock();
if (pending->lock == NULL) {
return _PyStatus_NO_MEMORY();
}

return _PyStatus_OK();
}

Expand Down Expand Up @@ -269,30 +261,6 @@ _PyEval_FiniThreads(struct _ceval_runtime_state *ceval)
}
}

/* This function is designed to exit daemon threads immediately rather than
taking the GIL if Py_Finalize() has been called.

The caller must *not* hold the GIL, since this function does not release
the GIL before exiting the thread.

When this function is called by a daemon thread after Py_Finalize() has been
called, the GIL does no longer exist.

tstate must be non-NULL. */
static inline void
exit_thread_if_finalizing(PyThreadState *tstate)
{
/* bpo-39877: Access _PyRuntime directly rather than using
tstate->interp->runtime to support calls from Python daemon threads.
After Py_Finalize() has been called, tstate can be a dangling pointer:
point to PyThreadState freed memory. */
_PyRuntimeState *runtime = &_PyRuntime;
PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(runtime);
if (finalizing != NULL && finalizing != tstate) {
PyThread_exit_thread();
}
}

void
_PyEval_Fini(void)
{
Expand Down Expand Up @@ -329,11 +297,7 @@ PyEval_AcquireLock(void)
PyThreadState *tstate = _PyRuntimeState_GetThreadState(runtime);
ensure_tstate_not_null(__func__, tstate);

exit_thread_if_finalizing(tstate);
assert(is_tstate_valid(tstate));

struct _ceval_runtime_state *ceval = &runtime->ceval;
take_gil(ceval, tstate);
take_gil(tstate);
}

void
Expand All @@ -353,17 +317,10 @@ PyEval_AcquireThread(PyThreadState *tstate)
{
ensure_tstate_not_null(__func__, tstate);

exit_thread_if_finalizing(tstate);
assert(is_tstate_valid(tstate));

_PyRuntimeState *runtime = tstate->interp->runtime;
struct _ceval_runtime_state *ceval = &runtime->ceval;

/* Check that _PyEval_InitThreads() was called to create the lock */
assert(gil_created(&ceval->gil));
take_gil(tstate);

take_gil(ceval, tstate);
if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
struct _gilstate_runtime_state *gilstate = &tstate->interp->runtime->gilstate;
if (_PyThreadState_Swap(gilstate, tstate) != NULL) {
Py_FatalError("non-NULL old thread state");
}
}
Expand Down Expand Up @@ -396,7 +353,8 @@ _PyEval_ReInitThreads(_PyRuntimeState *runtime)
recreate_gil(&ceval->gil);
PyThreadState *tstate = _PyRuntimeState_GetThreadState(runtime);
ensure_tstate_not_null(__func__, tstate);
take_gil(ceval, tstate);

take_gil(tstate);

struct _pending_calls *pending = &ceval->pending;
pending->lock = PyThread_allocate_lock();
Expand Down Expand Up @@ -436,16 +394,10 @@ PyEval_RestoreThread(PyThreadState *tstate)
{
ensure_tstate_not_null(__func__, tstate);

exit_thread_if_finalizing(tstate);
assert(is_tstate_valid(tstate));
take_gil(tstate);

_PyRuntimeState *runtime = tstate->interp->runtime;
struct _ceval_runtime_state *ceval = &runtime->ceval;
assert(gil_created(&ceval->gil));

take_gil(ceval, tstate);

_PyThreadState_Swap(&runtime->gilstate, tstate);
struct _gilstate_runtime_state *gilstate = &tstate->interp->runtime->gilstate;
_PyThreadState_Swap(gilstate, tstate);
}


Expand Down Expand Up @@ -805,7 +757,6 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)

PyThreadState * const tstate = _PyRuntimeState_GetThreadState(runtime);
ensure_tstate_not_null(__func__, tstate);
assert(is_tstate_valid(tstate));

/* when tracing we set things up so that

Expand Down Expand Up @@ -1294,10 +1245,7 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)

/* Other threads may run now */

/* Check if we should make a quick exit. */
exit_thread_if_finalizing(tstate);

take_gil(ceval, tstate);
take_gil(tstate);

if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
Py_FatalError("orphan tstate");
Expand Down
41 changes: 40 additions & 1 deletion Python/ceval_gil.h
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -180,17 +180,55 @@ drop_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
#endif
}


/* Check if a Python thread must exit immediately, rather than taking the GIL
if Py_Finalize() has been called.

When this function is called by a daemon thread after Py_Finalize() has been
called, the GIL does no longer exist.

tstate must be non-NULL. */
static inline int
tstate_must_exit(PyThreadState *tstate)
{
/* bpo-39877: Access _PyRuntime directly rather than using
tstate->interp->runtime to support calls from Python daemon threads.
After Py_Finalize() has been called, tstate can be a dangling pointer:
point to PyThreadState freed memory. */
_PyRuntimeState *runtime = &_PyRuntime;
PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(runtime);
return (finalizing != NULL && finalizing != tstate);
}


/* Take the GIL.

The function saves errno at entry and restores its value at exit.

tstate must be non-NULL. */
static void
take_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
take_gil(PyThreadState *tstate)
{
int err = errno;

assert(tstate != NULL);

/* Check if we should make a quick exit. */
if (tstate_must_exit(tstate)) {
PyThread_exit_thread();
}

/* Ensure that tstate is valid: sanity check for PyEval_AcquireThread() and
PyEval_RestoreThread(). Detect if tstate memory was freed. */
assert(!_PyMem_IsPtrFreed(tstate));
assert(!_PyMem_IsPtrFreed(tstate->interp));

struct _ceval_runtime_state *ceval = &tstate->interp->runtime->ceval;
struct _gil_runtime_state *gil = &ceval->gil;

/* Check that _PyEval_InitThreads() was called to create the lock */
assert(gil_created(gil));

MUTEX_LOCK(gil->mutex);

if (!_Py_atomic_load_relaxed(&gil->locked)) {
Expand All @@ -215,6 +253,7 @@ take_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
SET_GIL_DROP_REQUEST(ceval);
}
}

_ready:
#ifdef FORCE_SWITCHING
/* This mutex must be taken before modifying gil->last_holder:
Expand Down