8000 gh-59956: Clarify GILState-related Code by ericsnowcurrently · Pull Request #101161 · python/cpython · GitHub
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gh-59956: Clarify GILState-related Code #101161

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Merged
merged 11 commits into from
Jan 19, 2023
Merged

gh-59956: Clarify GILState-related Code #101161

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c35aee5
Add some TODO comments.
ericsnowcurrently Jan 18, 2023
bb86c59
Factor out "current_tss" helpers.
ericsnowcurrently Jan 18, 2023
5903b39
Inline the current_tss helpers.
ericsnowcurrently Jan 19, 2023
a5eb3d8
Factor out "current_fast" helpers.
ericsnowcurrently Jan 18, 2023
6281edb
Move tstate_current out of _PyRuntimeState.gilstate.
ericsnowcurrently Jan 18, 2023
2f8aaec
Do not use _PyThreadState_GET() in pystate.c.
ericsnowcurrently Jan 18, 2023
4af2ecb
Move autoTSSkey out of _PyRuntimeState.gilstate.
ericsnowcurrently Jan 19, 2023
7bdf5a4
Initialize autoTSSkey earlier.
ericsnowcurrently Jan 19, 2023
4b952e0
Factor out bind_tstate() and unbind_tstate().
ericsnowcurrently Jan 19, 2023
5e7283c
PyThreadState_IsCurrent() -> holds_gil().
ericsnowcurrently Jan 19, 2023
57bd92e
Do not set PyThreadState.thread_id to a negative value.
ericsnowcurrently Jan 19, 2023
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PyThreadState_IsCurrent() -> holds_gil().
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@ericsnowcurrently
ericsnowcurrently committed Jan 19, 2023
commit 5e7283c786a38c9bfd2154a7a2d6c16b464ab5f5
56 changes: 30 additions & 26 deletions Python/pystate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -206,6 +206,26 @@ unbind_tstate(PyThreadState *tstate)
tstate->native_thread_id = -1;
}

/* This is not exported, as it is not reliable! It can only
ever be compared to the state for the *current* thread.
* If not equal, then it doesn't matter that the actual
value may change immediately after comparison, as it can't
possibly change to the current thread's state.
* If equal, then the current thread holds the lock, so the value can't
change until we yield the lock.
*/
static int
holds_gil(PyThreadState *tstate)
{
// XXX Fall back to tstate->interp->runtime->ceval.gil.last_holder
// (and tstate->interp->runtime->ceval.gil.locked).
assert(tstate != NULL);
_PyRuntimeState *runtime = tstate->interp->runtime;
/* Must be the tstate for this thread */
assert(tstate == current_tss_get(runtime));
return tstate == current_fast_get(runtime);
}


/* the global runtime */

Expand Down Expand Up @@ -1410,6 +1430,7 @@ _PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
to be used for a thread. Check this the best we can in debug
builds.
*/
// XXX The above isn't true when multiple interpreters are involved.
#if defined(Py_DEBUG)
if (newts && current_tss_initialized(runtime)) {
/* This can be called from PyEval_RestoreThread(). Similar
Expand Down Expand Up @@ -1692,24 +1713,6 @@ _PyThread_CurrentExceptions(void)

/* Python "auto thread state" API. */

/* Keep this as a static, as it is not reliable! It can only
ever be compared to the state for the *current* thread.
* If not equal, then it doesn't matter that the actual
value may change immediately after comparison, as it can't
possibly change to the current thread's state.
* If equal, then the current thread holds the lock, so the value can't
change until we yield the lock.
*/
static int
PyThreadState_IsCurrent(PyThreadState *tstate)
{
assert(tstate != NULL);
_PyRuntimeState *runtime = tstate->interp->runtime;
/* Must be the tstate for this thread */
assert(tstate == current_tss_get(runtime));
return tstate == current_fast_get(runtime);
}

/* Internal initialization/finalization functions called by
Py_Initialize/Py_FinalizeEx
*/
Expand Down Expand Up @@ -1817,7 +1820,7 @@ PyGILState_Ensure(void)
assert(runtime->gilstate.autoInterpreterState != NULL);

PyThreadState *tcur = current_tss_get(runtime);
int current;
int has_gil;
if (tcur == NULL) {
/* Create a new Python thread state for this thread */
tcur = PyThreadState_New(runtime->gilstate.autoInterpreterState);
Expand All @@ -1829,13 +1832,13 @@ PyGILState_Ensure(void)
matching call to PyGILState_Release(). */
assert(tcur->gilstate_counter == 1);
tcur->gilstate_counter = 0;
current = 0; /* new thread state is never current */
has_gil = 0; /* new thread state is never current */
}
else {
current = PyThreadState_IsCurrent(tcur);
has_gil = holds_gil(tcur);
}

if (current == 0) {
if (!has_gil) {
PyEval_RestoreThread(tcur);
}

Expand All @@ -1846,7 +1849,7 @@ PyGILState_Ensure(void)
*/
++tcur->gilstate_counter;

return current ? PyGILState_LOCKED : PyGILState_UNLOCKED;
return has_gil ? PyGILState_LOCKED : PyGILState_UNLOCKED;
}

void
Expand All @@ -1864,12 +1867,12 @@ PyGILState_Release(PyGILState_STATE oldstate)
but while this is very new (April 2003), the extra check
by release-only users can't hurt.
*/
if (!PyThreadState_IsCurrent(tstate)) {
if (!holds_gil(tstate)) {
_Py_FatalErrorFormat(__func__,
"thread state %p must be current when releasing",
tstate);
}
assert(PyThreadState_IsCurrent(tstate));
assert(holds_gil(tstate));
--tstate->gilstate_counter;
assert(tstate->gilstate_counter >= 0); /* illegal counter value */

Expand All @@ -1889,8 +1892,9 @@ PyGILState_Release(PyGILState_STATE oldstate)
_PyThreadState_DeleteCurrent(tstate);
}
/* Release the lock if necessary */
else if (oldstate == PyGILState_UNLOCKED)
else if (oldstate == PyGILState_UNLOCKED) {
PyEval_SaveThread();
}
}


Expand Down
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