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[3.15] Fix _PyThreadState_ResumeDetached() assertion with attach waiters #159372

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Merged
nascheme merged 1 commit into from
Oct 13, 2026
Merged

[3.15] Fix _PyThreadState_ResumeDetached() assertion with attach waiters #159372

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5 changes: 3 additions & 2 deletions Include/internal/pycore_pystate.h
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Original file line number Diff line number Diff line change
Expand Up @@ -161,8 +161,9 @@ extern void _PyThreadState_Suspend(PyThreadState *tstate);
// Returns 1 on success, 0 if the thread was not in the "detached" state.
extern int _PyThreadState_TrySuspendDetached(PyThreadState *tstate);

// Undo a successful _PyThreadState_TrySuspendDetached(): switch the thread
// back to "detached" and wake it if it is waiting to attach.
// Resume a thread suspended by _PyThreadState_TrySuspendDetached() or a
// stop-the-world pause: switch it back to "detached" or "detached-waiting"
// and wake it if it is waiting to attach.
extern void _PyThreadState_ResumeDetached(PyThreadState *tstate);
#endif

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46 changes: 18 additions & 28 deletions Python/pystate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2401,10 +2401,24 @@ void
_PyThreadState_ResumeDetached(PyThreadState *tstate)
{
assert(tstate != _PyThreadState_GET());
assert(_Py_atomic_load_int_relaxed(&tstate->state) == _Py_THREAD_SUSPENDED);
_Py_atomic_store_int(&tstate->state, _Py_THREAD_DETACHED);
int state = _Py_atomic_load_int_relaxed(&tstate->state);
int next_state;
do {
assert(state == _Py_THREAD_SUSPENDED ||
state == _Py_THREAD_SUSPENDED_WAITING);
if (state == _Py_THREAD_SUSPENDED_WAITING) {
next_state = _Py_THREAD_DETACHED_WAITING;
}
else {
next_state = _Py_THREAD_DETACHED;
}
// Retry if an attach waiter registered concurrently.
} while (!_Py_atomic_compare_exchange_int(
&tstate->state, &state, next_state));
// Wake the thread if it is parked in tstate_wait_attach().
_PyParkingLot_UnparkAll(&tstate->state);
if (state == _Py_THREAD_SUSPENDED_WAITING) {
_PyParkingLot_UnparkAll(&tstate->state);
}
}
#endif

Expand Down Expand Up @@ -2526,30 +2540,6 @@ stop_the_world(struct _stoptheworld_state *stw)
stw->world_stopped = 1;
}

static void
tstate_resume(PyThreadState *tstate)
{
assert(tstate != _PyThreadState_GET());
int state = _Py_atomic_load_int_relaxed(&tstate->state);
int next_state;
do {
assert(state == _Py_THREAD_SUSPENDED ||
state == _Py_THREAD_SUSPENDED_WAITING);
if (state == _Py_THREAD_SUSPENDED_WAITING) {
next_state = _Py_THREAD_DETACHED_WAITING;
}
else {
next_state = _Py_THREAD_DETACHED;
}
// Retry if an attach waiter registered concurrently.
} while (!_Py_atomic_compare_exchange_int(
&tstate->state, &state, next_state));
// Wake the thread if it is parked in tstate_wait_attach().
if (state == _Py_THREAD_SUSPENDED_WAITING) {
_PyParkingLot_UnparkAll(&tstate->state);
}
}

static void
start_the_world(struct _stoptheworld_state *stw)
{
Expand All @@ -2563,7 +2553,7 @@ start_the_world(struct _stoptheworld_state *stw)
_Py_FOR_EACH_STW_INTERP(stw, i) {
_Py_FOR_EACH_TSTATE_UNLOCKED(i, t) {
if (t != stw->requester) {
tstate_resume(t);
_PyThreadState_ResumeDetached(t);
}
}
}
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