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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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19
Python/bytecodes.c
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@ -1312,14 +1312,13 @@ dummy_func(
assert(frame->owner != FRAME_OWNED_BY_INTERPRETER);
if ((tstate->interp->eval_frame == NULL) &&
(Py_TYPE(receiver_o) == &PyGen_Type || Py_TYPE(receiver_o) == &PyCoro_Type) &&
((PyGenObject *)receiver_o)->gi_frame_state < FRAME_EXECUTING)
gen_try_set_executing((PyGenObject *)receiver_o))
{
PyGenObject *gen = (PyGenObject *)receiver_o;
_PyInterpreterFrame *gen_frame = &gen->gi_iframe;
_PyFrame_StackPush(gen_frame, PyStackRef_MakeHeapSafe(v));
DEAD(v);
SYNC_SP();
gen->gi_frame_state = FRAME_EXECUTING;
gen->gi_exc_state.previous_item = tstate->exc_info;
tstate->exc_info = &gen->gi_exc_state;
assert(INSTRUCTION_SIZE + oparg <= UINT16_MAX);
@ -1360,12 +1359,11 @@ dummy_func(
op(_SEND_GEN_FRAME, (receiver, v -- receiver, gen_frame)) {
PyGenObject *gen = (PyGenObject *)PyStackRef_AsPyObjectBorrow(receiver);
DEOPT_IF(Py_TYPE(gen) != &PyGen_Type && Py_TYPE(gen) != &PyCoro_Type);
DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING);
DEOPT_IF(!gen_try_set_executing((PyGenObject *)gen));
STAT_INC(SEND, hit);
_PyInterpreterFrame *pushed_frame = &gen->gi_iframe;
_PyFrame_StackPush(pushed_frame, PyStackRef_MakeHeapSafe(v));
DEAD(v);
gen->gi_frame_state = FRAME_EXECUTING;
gen->gi_exc_state.previous_item = tstate->exc_info;
tstate->exc_info = &gen->gi_exc_state;
assert(INSTRUCTION_SIZE + oparg <= UINT16_MAX);
@ -1389,7 +1387,6 @@ dummy_func(
PyGenObject *gen = _PyGen_GetGeneratorFromFrame(frame);
assert(FRAME_SUSPENDED_YIELD_FROM == FRAME_SUSPENDED + 1);
assert(oparg == 0 || oparg == 1);
gen->gi_frame_state = FRAME_SUSPENDED + oparg;
_PyStackRef temp = retval;
DEAD(retval);
SAVE_STACK();
@ -1399,6 +1396,8 @@ dummy_func(
_PyInterpreterFrame *gen_frame = frame;
frame = tstate->current_frame = frame->previous;
gen_frame->previous = NULL;
((_PyThreadStateImpl *)tstate)->generator_return_kind = GENERATOR_YIELD;
FT_ATOMIC_STORE_INT8_RELEASE(gen->gi_frame_state, FRAME_SUSPENDED + oparg);
/* We don't know which of these is relevant here, so keep them equal */
assert(INLINE_CACHE_ENTRIES_SEND == INLINE_CACHE_ENTRIES_FOR_ITER);
#if TIER_ONE
@ -3405,18 +3404,10 @@ dummy_func(
op(_FOR_ITER_GEN_FRAME, (iter, null -- iter, null, gen_frame)) {
PyGenObject *gen = (PyGenObject *)PyStackRef_AsPyObjectBorrow(iter);
DEOPT_IF(Py_TYPE(gen) != &PyGen_Type);
#ifdef Py_GIL_DISABLED
// Since generators can't be used by multiple threads anyway we
// don't need to deopt here, but this lets us work on making
// generators thread-safe without necessarily having to
// specialize them thread-safely as well.
DEOPT_IF(!_PyObject_IsUniquelyReferenced((PyObject *)gen));
#endif
DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING);
DEOPT_IF(!gen_try_set_executing((PyGenObject *)gen));
STAT_INC(FOR_ITER, hit);
_PyInterpreterFrame *pushed_frame = &gen->gi_iframe;
_PyFrame_StackPush(pushed_frame, PyStackRef_None);
gen->gi_frame_state = FRAME_EXECUTING;
gen->gi_exc_state.previous_item = tstate->exc_info;
tstate->exc_info = &gen->gi_exc_state;
pushed_frame->previous = frame;