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pythongh-99113: Make Sure the GIL is Acquired at the Right Places (py…
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…thongh-104208)

This is a pre-requisite for a per-interpreter GIL.  Without it this change isn't strictly necessary.  However, there is no real downside otherwise.
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@ericsnowcurrently @jbower-fb
ericsnowcurrently authored and jbower-fb committed May 8, 2023
1 parent fc1e63f commit 74d38ea
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Showing 4 changed files with 113 additions and 40 deletions.
2 changes: 2 additions & 0 deletions Include/internal/pycore_ceval.h
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Original file line number Diff line number Diff line change
Expand Up @@ -100,7 +100,9 @@ extern int _PyEval_ThreadsInitialized(void);
extern PyStatus _PyEval_InitGIL(PyThreadState *tstate, int own_gil);
extern void _PyEval_FiniGIL(PyInterpreterState *interp);

extern void _PyEval_AcquireLock(PyThreadState *tstate);
extern void _PyEval_ReleaseLock(PyThreadState *tstate);
extern PyThreadState * _PyThreadState_SwapNoGIL(PyThreadState *);

extern void _PyEval_DeactivateOpCache(void);

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84 changes: 57 additions & 27 deletions Python/ceval_gil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -499,42 +499,66 @@ PyEval_ThreadsInitialized(void)
return _PyEval_ThreadsInitialized();
}

static inline int
current_thread_holds_gil(struct _gil_runtime_state *gil, PyThreadState *tstate)
{
if (((PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) != tstate) {
return 0;
}
return _Py_atomic_load_relaxed(&gil->locked);
}

static void
init_shared_gil(PyInterpreterState *interp, struct _gil_runtime_state *gil)
{
assert(gil_created(gil));
interp->ceval.gil = gil;
interp->ceval.own_gil = 0;
}

static void
init_own_gil(PyInterpreterState *interp, struct _gil_runtime_state *gil)
{
assert(!gil_created(gil));
create_gil(gil);
assert(gil_created(gil));
interp->ceval.gil = gil;
interp->ceval.own_gil = 1;
}

PyStatus
_PyEval_InitGIL(PyThreadState *tstate, int own_gil)
{
assert(tstate->interp->ceval.gil == NULL);
int locked;
if (!own_gil) {
PyInterpreterState *main_interp = _PyInterpreterState_Main();
assert(tstate->interp != main_interp);
struct _gil_runtime_state *gil = main_interp->ceval.gil;
assert(gil_created(gil));
tstate->interp->ceval.gil = gil;
tstate->interp->ceval.own_gil = 0;
return _PyStatus_OK();
init_shared_gil(tstate->interp, gil);
locked = current_thread_holds_gil(gil, tstate);
}

/* XXX per-interpreter GIL */
struct _gil_runtime_state *gil = &tstate->interp->runtime->ceval.gil;
if (!_Py_IsMainInterpreter(tstate->interp)) {
else if (!_Py_IsMainInterpreter(tstate->interp)) {
/* Currently, the GIL is shared by all interpreters,
and only the main interpreter is responsible to create
and destroy it. */
assert(gil_created(gil));
tstate->interp->ceval.gil = gil;
struct _gil_runtime_state *main_gil = _PyInterpreterState_Main()->ceval.gil;
init_shared_gil(tstate->interp, main_gil);
// XXX For now we lie.
tstate->interp->ceval.own_gil = 1;
return _PyStatus_OK();
locked = current_thread_holds_gil(main_gil, tstate);
}
else {
PyThread_init_thread();
// XXX per-interpreter GIL: switch to interp->_gil.
init_own_gil(tstate->interp, &tstate->interp->runtime->ceval.gil);
locked = 0;
}
if (!locked) {
take_gil(tstate);
}
assert(own_gil);

assert(!gil_created(gil));

PyThread_init_thread();
create_gil(gil);
assert(gil_created(gil));
tstate->interp->ceval.gil = gil;
tstate->interp->ceval.own_gil = 1;
take_gil(tstate);
return _PyStatus_OK();
}

Expand Down Expand Up @@ -611,9 +635,17 @@ PyEval_ReleaseLock(void)
drop_gil(ceval, tstate);
}

void
_PyEval_AcquireLock(PyThreadState *tstate)
{
_Py_EnsureTstateNotNULL(tstate);
take_gil(tstate);
}

void
_PyEval_ReleaseLock(PyThreadState *tstate)
{
_Py_EnsureTstateNotNULL(tstate);
struct _ceval_state *ceval = &tstate->interp->ceval;
drop_gil(ceval, tstate);
}
Expand All @@ -625,7 +657,7 @@ PyEval_AcquireThread(PyThreadState *tstate)

take_gil(tstate);

if (_PyThreadState_Swap(tstate->interp->runtime, tstate) != NULL) {
if (_PyThreadState_SwapNoGIL(tstate) != NULL) {
Py_FatalError("non-NULL old thread state");
}
}
Expand All @@ -635,8 +667,7 @@ PyEval_ReleaseThread(PyThreadState *tstate)
{
assert(is_tstate_valid(tstate));

_PyRuntimeState *runtime = tstate->interp->runtime;
PyThreadState *new_tstate = _PyThreadState_Swap(runtime, NULL);
PyThreadState *new_tstate = _PyThreadState_SwapNoGIL(NULL);
if (new_tstate != tstate) {
Py_FatalError("wrong thread state");
}
Expand Down Expand Up @@ -684,8 +715,7 @@ _PyEval_SignalAsyncExc(PyInterpreterState *interp)
PyThreadState *
PyEval_SaveThread(void)
{
_PyRuntimeState *runtime = &_PyRuntime;
PyThreadState *tstate = _PyThreadState_Swap(runtime, NULL);
PyThreadState *tstate = _PyThreadState_SwapNoGIL(NULL);
_Py_EnsureTstateNotNULL(tstate);

struct _ceval_state *ceval = &tstate->interp->ceval;
Expand All @@ -701,7 +731,7 @@ PyEval_RestoreThread(PyThreadState *tstate)

take_gil(tstate);

_PyThreadState_Swap(tstate->interp->runtime, tstate);
_PyThreadState_SwapNoGIL(tstate);
}


Expand Down Expand Up @@ -1005,7 +1035,7 @@ _Py_HandlePending(PyThreadState *tstate)
/* GIL drop request */
if (_Py_atomic_load_relaxed_int32(&interp_ceval_state->gil_drop_request)) {
/* Give another thread a chance */
if (_PyThreadState_Swap(runtime, NULL) != tstate) {
if (_PyThreadState_SwapNoGIL(NULL) != tstate) {
Py_FatalError("tstate mix-up");
}
drop_gil(interp_ceval_state, tstate);
Expand All @@ -1014,7 +1044,7 @@ _Py_HandlePending(PyThreadState *tstate)

take_gil(tstate);

if (_PyThreadState_Swap(runtime, tstate) != NULL) {
if (_PyThreadState_SwapNoGIL(tstate) != NULL) {
Py_FatalError("orphan tstate");
}
}
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25 changes: 22 additions & 3 deletions Python/pylifecycle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -591,6 +591,7 @@ init_interp_create_gil(PyThreadState *tstate, int own_gil)

/* finalize_interp_delete() comment explains why _PyEval_FiniGIL() is
only called here. */
// XXX This is broken with a per-interpreter GIL.
_PyEval_FiniGIL(tstate->interp);

/* Auto-thread-state API */
Expand Down Expand Up @@ -645,7 +646,8 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
return _PyStatus_ERR("can't make first thread");
}
_PyThreadState_Bind(tstate);
(void) PyThreadState_Swap(tstate);
// XXX For now we do this before the GIL is created.
(void) _PyThreadState_SwapNoGIL(tstate);

status = init_interp_create_gil(tstate, config.own_gil);
if (_PyStatus_EXCEPTION(status)) {
Expand Down Expand Up @@ -2025,11 +2027,20 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
}
_PyThreadState_Bind(tstate);

PyThreadState *save_tstate = PyThreadState_Swap(tstate);
// XXX For now we do this before the GIL is created.
PyThreadState *save_tstate = _PyThreadState_SwapNoGIL(tstate);
int has_gil = 0;

/* From this point until the init_interp_create_gil() call,
we must not do anything that requires that the GIL be held
(or otherwise exist). That applies whether or not the new
interpreter has its own GIL (e.g. the main interpreter). */

/* Copy the current interpreter config into the new interpreter */
const PyConfig *src_config;
if (save_tstate != NULL) {
// XXX Might new_interpreter() have been called without the GIL held?
_PyEval_ReleaseLock(save_tstate);
src_config = _PyInterpreterState_GetConfig(save_tstate->interp);
}
else
Expand All @@ -2039,11 +2050,13 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
src_config = _PyInterpreterState_GetConfig(main_interp);
}

/* This does not require that the GIL be held. */
status = _PyConfig_Copy(&interp->config, src_config);
if (_PyStatus_EXCEPTION(status)) {
goto error;
}

/* This does not require that the GIL be held. */
status = init_interp_settings(interp, config);
if (_PyStatus_EXCEPTION(status)) {
goto error;
Expand All @@ -2053,6 +2066,7 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
if (_PyStatus_EXCEPTION(status)) {
goto error;
}
has_gil = 1;

status = pycore_interp_init(tstate);
if (_PyStatus_EXCEPTION(status)) {
Expand All @@ -2072,7 +2086,12 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)

/* Oops, it didn't work. Undo it all. */
PyErr_PrintEx(0);
PyThreadState_Swap(save_tstate);
if (has_gil) {
PyThreadState_Swap(save_tstate);
}
else {
_PyThreadState_SwapNoGIL(save_tstate);
}
PyThreadState_Clear(tstate);
PyThreadState_Delete(tstate);
PyInterpreterState_Delete(interp);
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42 changes: 32 additions & 10 deletions Python/pystate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1863,17 +1863,11 @@ PyThreadState_Get(void)
}


PyThreadState *
_PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
static void
_swap_thread_states(_PyRuntimeState *runtime,
PyThreadState *oldts, PyThreadState *newts)
{
#if defined(Py_DEBUG)
/* This can be called from PyEval_RestoreThread(). Similar
to it, we need to ensure errno doesn't change.
*/
int err = errno;
#endif
PyThreadState *oldts = current_fast_get(runtime);

// XXX Do this only if oldts != NULL?
current_fast_clear(runtime);

if (oldts != NULL) {
Expand All @@ -1887,13 +1881,41 @@ _PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
current_fast_set(runtime, newts);
tstate_activate(newts);
}
}

PyThreadState *
_PyThreadState_SwapNoGIL(PyThreadState *newts)
{
#if defined(Py_DEBUG)
/* This can be called from PyEval_RestoreThread(). Similar
to it, we need to ensure errno doesn't change.
*/
int err = errno;
#endif

PyThreadState *oldts = current_fast_get(&_PyRuntime);
_swap_thread_states(&_PyRuntime, oldts, newts);

#if defined(Py_DEBUG)
errno = err;
#endif
return oldts;
}

PyThreadState *
_PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
{
PyThreadState *oldts = current_fast_get(runtime);
if (oldts != NULL) {
_PyEval_ReleaseLock(oldts);
}
_swap_thread_states(runtime, oldts, newts);
if (newts != NULL) {
_PyEval_AcquireLock(newts);
}
return oldts;
}

PyThreadState *
PyThreadState_Swap(PyThreadState *newts)
{
Expand Down

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