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gh-109693: Update _gil_runtime_state.last_holder to use pyatomic.h #110605

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Merged
merged 1 commit into from
Oct 13, 2023
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gh-109693: Update _gil_runtime_state.last_holder to use pyatomic.h #110605

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4 changes: 2 additions & 2 deletions Include/internal/pycore_gil.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ extern "C" {
# error "this header requires Py_BUILD_CORE define"
#endif

#include "pycore_atomic.h" // _Py_atomic_address
#include "pycore_atomic.h" // _Py_atomic_int
#include "pycore_condvar.h" // PyCOND_T

#ifndef Py_HAVE_CONDVAR
Expand All @@ -25,7 +25,7 @@ struct _gil_runtime_state {
unsigned long interval;
/* Last PyThreadState holding / having held the GIL. This helps us
know whether anyone else was scheduled after we dropped the GIL. */
_Py_atomic_address last_holder;
PyThreadState* last_holder;
/* Whether the GIL is already taken (-1 if uninitialized). This is
atomic because it can be read without any lock taken in ceval.c. */
_Py_atomic_int locked;
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@vstinner @colesbury

cpython/Python/ceval_gil.c

Line 179 in 982f1b7

return (_Py_atomic_load_explicit(&gil->locked, _Py_memory_order_acquire) >= 0);

cpython/Python/ceval_gil.c

Line 194 in 982f1b7

_Py_atomic_store_explicit(&gil->locked, 0, _Py_memory_order_release);

IIUC, To update locked field we need to introduce _Py_atomic_load/store_int_release/acquire

Do you have better ideas?

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@vstinner vstinner Oct 10, 2023 •
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It sounds like a good idea, for another API

EDIT: Oops, I wrote PEP not API, sorry about that :-D Need more coffee.

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14 changes: 7 additions & 7 deletions Python/ceval_gil.c
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Expand Up @@ -189,7 +189,7 @@ static void create_gil(struct _gil_runtime_state *gil)
#ifdef FORCE_SWITCHING
COND_INIT(gil->switch_cond);
#endif
_Py_atomic_store_relaxed(&gil->last_holder, 0);
_Py_atomic_store_ptr_relaxed(&gil->last_holder, 0);
_Py_ANNOTATE_RWLOCK_CREATE(&gil->locked);
_Py_atomic_store_explicit(&gil->locked, 0, _Py_memory_order_release);
}
Expand Down Expand Up @@ -233,7 +233,7 @@ drop_gil(PyInterpreterState *interp, PyThreadState *tstate)
// XXX assert(tstate == NULL || !tstate->_status.cleared);

struct _gil_runtime_state *gil = ceval->gil;
if (!_Py_atomic_load_relaxed(&gil->locked)) {
if (!_Py_atomic_load_ptr_relaxed(&gil->locked)) {
Py_FatalError("drop_gil: GIL is not locked");
}

Expand All @@ -242,7 +242,7 @@ drop_gil(PyInterpreterState *interp, PyThreadState *tstate)
/* Sub-interpreter support: threads might have been switched
under our feet using PyThreadState_Swap(). Fix the GIL last
holder variable so that our heuristics work. */
_Py_atomic_store_relaxed(&gil->last_holder, (uintptr_t)tstate);
_Py_atomic_store_ptr_relaxed(&gil->last_holder, tstate);
}

MUTEX_LOCK(gil->mutex);
Expand All @@ -263,7 +263,7 @@ drop_gil(PyInterpreterState *interp, PyThreadState *tstate)
if (tstate != NULL && _Py_eval_breaker_bit_is_set(interp, _PY_GIL_DROP_REQUEST_BIT)) {
MUTEX_LOCK(gil->switch_mutex);
/* Not switched yet => wait */
if (((PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) == tstate)
if (((PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) == tstate)
{
assert(_PyThreadState_CheckConsistency(tstate));
RESET_GIL_DROP_REQUEST(tstate->interp);
Expand Down Expand Up @@ -361,8 +361,8 @@ take_gil(PyThreadState *tstate)
_Py_atomic_store_relaxed(&gil->locked, 1);
_Py_ANNOTATE_RWLOCK_ACQUIRED(&gil->locked, /*is_write=*/1);

if (tstate != (PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) {
_Py_atomic_store_relaxed(&gil->last_holder, (uintptr_t)tstate);
if (tstate != (PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) {
_Py_atomic_store_ptr_relaxed(&gil->last_holder, tstate);
++gil->switch_number;
}

Expand Down Expand Up @@ -434,7 +434,7 @@ PyEval_ThreadsInitialized(void)
static inline int
current_thread_holds_gil(struct _gil_runtime_state *gil, PyThreadState *tstate)
{
if (((PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) != tstate) {
if (((PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) != tstate) {
return 0;
}
return _Py_atomic_load_relaxed(&gil->locked);
Expand Down