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gh-120321: Make gi_frame_state transitions atomic in FT build (gh-142599)

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This makes generator frame state transitions atomic in the free
threading build, which avoids segfaults when trying to execute
a generator from multiple threads concurrently.

There are still a few operations that aren't thread-safe and may crash
if performed concurrently on the same generator/coroutine:

 * Accessing gi_yieldfrom/cr_await/ag_await
 * Accessing gi_frame/cr_frame/ag_frame
 * Async generator operations
This commit is contained in:
Sam Gross 2025-12-19 14:10:37 -05:00 • committed by GitHub
parent e2a7db7175
commit 08bc03ff2a
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GPG key ID: B5690EEEBB952194
16 changed files with 1124 additions and 883 deletions
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15
Python/ceval.c
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@ -2304,7 +2304,8 @@ clear_gen_frame(PyThreadState *tstate, _PyInterpreterFrame * frame)
{
assert(frame->owner == FRAME_OWNED_BY_GENERATOR);
PyGenObject *gen = _PyGen_GetGeneratorFromFrame(frame);
gen->gi_frame_state = FRAME_CLEARED;
FT_ATOMIC_STORE_INT8_RELEASE(gen->gi_frame_state, FRAME_CLEARED);
((_PyThreadStateImpl *)tstate)->generator_return_kind = GENERATOR_RETURN;
assert(tstate->exc_info == &gen->gi_exc_state);
tstate->exc_info = gen->gi_exc_state.previous_item;
gen->gi_exc_state.previous_item = NULL;
@ -3979,15 +3980,13 @@ _PyEval_GetAwaitable(PyObject *iterable, int oparg)
Py_TYPE(iterable), oparg);
}
else if (PyCoro_CheckExact(iter)) {
PyObject *yf = _PyGen_yf((PyGenObject*)iter);
if (yf != NULL) {
/* `iter` is a coroutine object that is being
awaited, `yf` is a pointer to the current awaitable
being awaited on. */
Py_DECREF(yf);
PyCoroObject *coro = (PyCoroObject *)iter;
int8_t frame_state = FT_ATOMIC_LOAD_INT8_RELAXED(coro->cr_frame_state);
if (frame_state == FRAME_SUSPENDED_YIELD_FROM) {
/* `iter` is a coroutine object that is being awaited. */
Py_CLEAR(iter);
_PyErr_SetString(PyThreadState_GET(), PyExc_RuntimeError,
"coroutine is being awaited already");
"coroutine is being awaited already");
}
}
return iter;