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gh-152741: Publish thread states to the interpreter's thread list only after they are fully initialized #156202

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gh-152741: Publish thread states to the interpreter's thread list only after they are fully initialized #156202

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gh-152741: Publish thread states to the interpreter's thread list onl…
kumaraditya303 Aug 21, 2026
5d1fcf7
fix eval breaker version
kumaraditya303 Aug 22, 2026
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71 changes: 45 additions & 26 deletions Python/pystate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,8 @@ static void bind_gilstate_tstate(PyThreadState *);
static void unbind_gilstate_tstate(PyThreadState *);

static void tstate_mimalloc_bind(PyThreadState *);
static void add_threadstate(PyInterpreterState *interp, PyThreadState *tstate,
PyThreadState *next);

static void
bind_tstate(PyThreadState *tstate)
Expand Down Expand Up @@ -190,6 +192,18 @@ bind_tstate(PyThreadState *tstate)
tstate_mimalloc_bind(tstate);

tstate->_status.bound = 1;

// Publish the thread state to the interpreter's thread list only now
// that it is fully initialized, so that readers of the list never see
// a partially initialized thread state.
PyInterpreterState *interp = tstate->interp;
HEAD_LOCK(interp->runtime);
if (interp->stoptheworld.requested || _PyRuntime.stoptheworld.requested) {
// Start in the suspended state if there is an ongoing stop-the-world.
tstate->state = _Py_THREAD_SUSPENDED;
}
add_threadstate(interp, tstate, interp->threads.head);
HEAD_UNLOCK(interp->runtime);
}

static void
Expand Down Expand Up @@ -1561,8 +1575,7 @@ init_threadstate(_PyThreadStateImpl *_tstate,

assert(interp != NULL);
tstate->interp = interp;
tstate->eval_breaker =
_Py_atomic_load_uintptr_relaxed(&interp->ceval.instrumentation_version);
// eval_breaker is set in add_threadstate().

// next/prev are set in add_threadstate().
assert(tstate->next == NULL);
Expand Down Expand Up @@ -1638,10 +1651,6 @@ init_threadstate(_PyThreadStateImpl *_tstate,

llist_init(&_tstate->mem_free_queue);
llist_init(&_tstate->asyncio_tasks_head);
if (interp->stoptheworld.requested || _PyRuntime.stoptheworld.requested) {
// Start in the suspended state if there is an ongoing stop-the-world.
tstate->state = _Py_THREAD_SUSPENDED;
}

tstate->_status.initialized = 1;
}
Expand All @@ -1651,6 +1660,11 @@ add_threadstate(PyInterpreterState *interp, PyThreadState *tstate,
PyThreadState *next)
{
assert(interp->threads.head != tstate);
// Set the instrumentation version, which in the free-threaded build is
// broadcast to the thread states on the interpreter's thread list.
uintptr_t version = _Py_atomic_load_uintptr_relaxed(
&interp->ceval.instrumentation_version);
_Py_atomic_or_uintptr(&tstate->eval_breaker, version);
if (next != NULL) {
assert(next->prev == NULL || next->prev == tstate);
next->prev = tstate;
Expand Down Expand Up @@ -1699,10 +1713,6 @@ new_threadstate(PyInterpreterState *interp, int whence)
uint64_t id = interp->threads.next_unique_id;
init_threadstate(tstate, interp, id, whence);

// Add the new thread state to the interpreter.
PyThreadState *old_head = interp->threads.head;
add_threadstate(interp, (PyThreadState *)tstate, old_head);

HEAD_UNLOCK(interp->runtime);

#ifdef Py_GIL_DISABLED
Expand Down Expand Up @@ -1930,24 +1940,33 @@ tstate_delete_common(PyThreadState *tstate, int release_gil)
_PyRuntimeState *runtime = interp->runtime;

HEAD_LOCK(runtime);
if (tstate->prev) {
tstate->prev->next = tstate->next;
}
else {
interp->threads.head = tstate->next;
}
if (tstate->next) {
tstate->next->prev = tstate->prev;
}
if (tstate->state != _Py_THREAD_SUSPENDED) {
// Any ongoing stop-the-world request should not wait for us because
// our thread is getting deleted.
if (interp->stoptheworld.requested) {
decrement_stoptheworld_countdown(&interp->stoptheworld);
if (tstate->_status.bound) {
if (tstate->prev) {
tstate->prev->next = tstate->next;
}
if (runtime->stoptheworld.requested) {
decrement_stoptheworld_countdown(&runtime->stoptheworld);
else {
interp->threads.head = tstate->next;
}
if (tstate->next) {
tstate->next->prev = tstate->prev;
}
if (tstate->state != _Py_THREAD_SUSPENDED) {
// Any ongoing stop-the-world request should not wait for us
// because our thread is getting deleted.
if (interp->stoptheworld.requested) {
decrement_stoptheworld_countdown(&interp->stoptheworld);
}
if (runtime->stoptheworld.requested) {
decrement_stoptheworld_countdown(&runtime->stoptheworld);
}
}
}
else {
// The thread state was never bound, so it was never added to the
// interpreter's thread list and no stop-the-world request is
// waiting on it.
assert(tstate->prev == NULL && tstate->next == NULL);
assert(interp->threads.head != tstate);
}

#if defined(Py_REF_DEBUG) && defined(Py_GIL_DISABLED)
Expand Down
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