#include "Python.h"

#include "pycore_ceval.h" // _PyEval_SignalReceived()

#include "pycore_gc.h" // _Py_RunGC()

#include "pycore_initconfig.h" // _PyStatus_OK()

#include "pycore_optimizer.h" // _Py_Executors_InvalidateCold()

#include "pycore_pyerrors.h" // _PyErr_GetRaisedException()

#include "pycore_pylifecycle.h" // _PyErr_Print()

#include "pycore_pystats.h" // _Py_PrintSpecializationStats()

#include "pycore_runtime.h" // _PyRuntime

/*

Notes about the implementation:

- The GIL is just a boolean variable (locked) whose access is protected

by a mutex (gil_mutex), and whose changes are signalled by a condition

variable (gil_cond). gil_mutex is taken for short periods of time,

and therefore mostly uncontended.

- In the GIL-holding thread, the main loop (PyEval_EvalFrameEx) must be

able to release the GIL on demand by another thread. A volatile boolean

variable (gil_drop_request) is used for that purpose, which is checked

at every turn of the eval loop. That variable is set after a wait of

`interval` microseconds on `gil_cond` has timed out.

[Actually, another volatile boolean variable (eval_breaker) is used

which ORs several conditions into one. Volatile booleans are

sufficient as inter-thread signalling means since Python is run

on cache-coherent architectures only.]

- A thread wanting to take the GIL will first let pass a given amount of

time (`interval` microseconds) before setting gil_drop_request. This

encourages a defined switching period, but doesn't enforce it since

opcodes can take an arbitrary time to execute.

The `interval` value is available for the user to read and modify

using the Python API `sys.{get,set}switchinterval()`.

- When a thread releases the GIL and gil_drop_request is set, that thread

ensures that another GIL-awaiting thread gets scheduled.

It does so by waiting on a condition variable (switch_cond) until

the value of last_holder is changed to something else than its

own thread state pointer, indicating that another thread was able to

take the GIL.

This is meant to prohibit the latency-adverse behaviour on multi-core

machines where one thread would speculatively release the GIL, but still

run and end up being the first to re-acquire it, making the "timeslices"

much longer than expected.

(Note: this mechanism is enabled with FORCE_SWITCHING above)

*/

// Atomically copy the bits indicated by mask between two values.

static inline void

copy_eval_breaker_bits(uintptr_t *from, uintptr_t *to, uintptr_t mask)

{

uintptr_t from_bits = _Py_atomic_load_uintptr_relaxed(from) & mask;

uintptr_t old_value = _Py_atomic_load_uintptr_relaxed(to);

uintptr_t to_bits = old_value & mask;

if (from_bits == to_bits) {

return;

}

uintptr_t new_value;

do {

new_value = (old_value & ~mask) | from_bits;

} while (!_Py_atomic_compare_exchange_uintptr(to, &old_value, new_value));

}

// When attaching a thread, set the global instrumentation version and

// _PY_CALLS_TO_DO_BIT from the current state of the interpreter.

static inline void

update_eval_breaker_for_thread(PyInterpreterState *interp, PyThreadState *tstate)

{

#ifdef Py_GIL_DISABLED

// Free-threaded builds eagerly update the eval_breaker on *all* threads as

// needed, so this function doesn't apply.

return;

#endif

int32_t npending = _Py_atomic_load_int32_relaxed(

&interp->ceval.pending.npending);

if (npending) {

_Py_set_eval_breaker_bit(tstate, _PY_CALLS_TO_DO_BIT);

}

else if (_Py_IsMainThread()) {

npending = _Py_atomic_load_int32_relaxed(

&_PyRuntime.ceval.pending_mainthread.npending);

if (npending) {

_Py_set_eval_breaker_bit(tstate, _PY_CALLS_TO_DO_BIT);

}

}

// _PY_CALLS_TO_DO_BIT was derived from other state above, so the only bits

// we copy from our interpreter's state are the instrumentation version.

copy_eval_breaker_bits(&interp->ceval.instrumentation_version,

&tstate->eval_breaker,

~_PY_EVAL_EVENTS_MASK);

}

/*

* Implementation of the Global Interpreter Lock (GIL).

*/

#include <stdlib.h>

#include <errno.h>

#include "condvar.h"

#define MUTEX_INIT(mut) \

if (PyMUTEX_INIT(&(mut))) { \

Py_FatalError("PyMUTEX_INIT(" #mut ") failed"); };

#define MUTEX_FINI(mut) \

if (PyMUTEX_FINI(&(mut))) { \

Py_FatalError("PyMUTEX_FINI(" #mut ") failed"); };

#define MUTEX_LOCK(mut) \

if (PyMUTEX_LOCK(&(mut))) { \

Py_FatalError("PyMUTEX_LOCK(" #mut ") failed"); };

#define MUTEX_UNLOCK(mut) \

if (PyMUTEX_UNLOCK(&(mut))) { \

Py_FatalError("PyMUTEX_UNLOCK(" #mut ") failed"); };

#define COND_INIT(cond) \

if (PyCOND_INIT(&(cond))) { \

Py_FatalError("PyCOND_INIT(" #cond ") failed"); };

#define COND_FINI(cond) \

if (PyCOND_FINI(&(cond))) { \

Py_FatalError("PyCOND_FINI(" #cond ") failed"); };

#define COND_SIGNAL(cond) \

if (PyCOND_SIGNAL(&(cond))) { \

Py_FatalError("PyCOND_SIGNAL(" #cond ") failed"); };

#define COND_WAIT(cond, mut) \

if (PyCOND_WAIT(&(cond), &(mut))) { \

Py_FatalError("PyCOND_WAIT(" #cond ") failed"); };

#define COND_TIMED_WAIT(cond, mut, microseconds, timeout_result) \

{ \

int r = PyCOND_TIMEDWAIT(&(cond), &(mut), (microseconds)); \

if (r < 0) \

Py_FatalError("PyCOND_WAIT(" #cond ") failed"); \

if (r) /* 1 == timeout, 2 == impl. can't say, so assume timeout */ \

timeout_result = 1; \

else \

timeout_result = 0; \

} \

#define DEFAULT_INTERVAL 5000

static void _gil_initialize(struct _gil_runtime_state *gil)

{

gil->locked = -1;

gil->interval = DEFAULT_INTERVAL;

}

static int gil_created(struct _gil_runtime_state *gil)

{

if (gil == NULL) {

return 0;

}

return (_Py_atomic_load_int_acquire(&gil->locked) >= 0);

}

static void create_gil(struct _gil_runtime_state *gil)

{

MUTEX_INIT(gil->mutex);

#ifdef FORCE_SWITCHING

MUTEX_INIT(gil->switch_mutex);

#endif

COND_INIT(gil->cond);

#ifdef FORCE_SWITCHING

COND_INIT(gil->switch_cond);

#endif

_Py_atomic_store_ptr_relaxed(&gil->last_holder, 0);

_Py_ANNOTATE_RWLOCK_CREATE(&gil->locked);

_Py_atomic_store_int_release(&gil->locked, 0);

}

static void destroy_gil(struct _gil_runtime_state *gil)

{

/* some pthread-like implementations tie the mutex to the cond

* and must have the cond destroyed first.

*/

COND_FINI(gil->cond);

MUTEX_FINI(gil->mutex);

#ifdef FORCE_SWITCHING

COND_FINI(gil->switch_cond);

MUTEX_FINI(gil->switch_mutex);

#endif

_Py_atomic_store_int_release(&gil->locked, -1);

_Py_ANNOTATE_RWLOCK_DESTROY(&gil->locked);

}

#ifdef HAVE_FORK

static void recreate_gil(struct _gil_runtime_state *gil)

{

_Py_ANNOTATE_RWLOCK_DESTROY(&gil->locked);

/* XXX should we destroy the old OS resources here? */

create_gil(gil);

}

#endif

static inline void

drop_gil_impl(PyThreadState *tstate, struct _gil_runtime_state *gil)

{

MUTEX_LOCK(gil->mutex);

_Py_ANNOTATE_RWLOCK_RELEASED(&gil->locked, /*is_write=*/1);

_Py_atomic_store_int_relaxed(&gil->locked, 0);

if (tstate != NULL) {

tstate->holds_gil = 0;

}

COND_SIGNAL(gil->cond);

MUTEX_UNLOCK(gil->mutex);

}

static void

drop_gil(PyInterpreterState *interp, PyThreadState *tstate, int final_release)

{

struct _ceval_state *ceval = &interp->ceval;

/* If final_release is true, the caller is indicating that we're releasing

the GIL for the last time in this thread. This is particularly

relevant when the current thread state is finalizing or its

interpreter is finalizing (either may be in an inconsistent

state). In that case the current thread will definitely

never try to acquire the GIL again. */

// XXX It may be more correct to check tstate->_status.finalizing.

// XXX assert(final_release || !tstate->_status.cleared);

assert(final_release || tstate != NULL);

struct _gil_runtime_state *gil = ceval->gil;

#ifdef Py_GIL_DISABLED

// Check if we have the GIL before dropping it. tstate will be NULL if

// take_gil() detected that this thread has been destroyed, in which case

// we know we have the GIL.

if (tstate != NULL && !tstate->holds_gil) {

return;

}

#endif

if (!_Py_atomic_load_int_relaxed(&gil->locked)) {

Py_FatalError("drop_gil: GIL is not locked");

}

if (!final_release) {

/* 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_ptr_relaxed(&gil->last_holder, tstate);

}

drop_gil_impl(tstate, gil);

#ifdef FORCE_SWITCHING

/* We might be releasing the GIL for the last time in this thread. In that

case there's a possible race with tstate->interp getting deleted after

gil->mutex is unlocked and before the following code runs, leading to a

crash. We can use final_release to indicate the thread is done with the

GIL, and that's the only time we might delete the interpreter. See

https://github.com/python/cpython/issues/104341. */

if (!final_release &&

_Py_eval_breaker_bit_is_set(tstate, _PY_GIL_DROP_REQUEST_BIT)) {

MUTEX_LOCK(gil->switch_mutex);

/* Not switched yet => wait */

if (((PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) == tstate)

{

assert(_PyThreadState_CheckConsistency(tstate));

_Py_unset_eval_breaker_bit(tstate, _PY_GIL_DROP_REQUEST_BIT);

/* NOTE: if COND_WAIT does not atomically start waiting when

releasing the mutex, another thread can run through, take

the GIL and drop it again, and reset the condition

before we even had a chance to wait for it. */

COND_WAIT(gil->switch_cond, gil->switch_mutex);

}

MUTEX_UNLOCK(gil->switch_mutex);

}

#endif

}

/* Take the GIL.

The function saves errno at entry and restores its value at exit.

It may hang rather than return if the interpreter has been finalized.

tstate must be non-NULL. */

static void

take_gil(PyThreadState *tstate)

{

int err = errno;

assert(tstate != NULL);

/* We shouldn't be using a thread state that isn't viable any more. */

// XXX It may be more correct to check tstate->_status.finalizing.

// XXX assert(!tstate->_status.cleared);

if (_PyThreadState_MustExit(tstate)) {

/* bpo-39877: If Py_Finalize() has been called and tstate is not the

thread which called Py_Finalize(), this thread cannot continue.

This code path can be reached by a daemon thread after Py_Finalize()

completes.

This used to call a *thread_exit API, but that was not safe as it

lacks stack unwinding and local variable destruction important to

C++. gh-87135: The best that can be done is to hang the thread as

the public APIs calling this have no error reporting mechanism (!).

*/

_PyThreadState_HangThread(tstate);

}

assert(_PyThreadState_CheckConsistency(tstate));

PyInterpreterState *interp = tstate->interp;

struct _gil_runtime_state *gil = interp->ceval.gil;

#ifdef Py_GIL_DISABLED

if (!_Py_atomic_load_int_relaxed(&gil->enabled)) {

return;

}

#endif

/* Check that _PyEval_InitThreads() was called to create the lock */

assert(gil_created(gil));

MUTEX_LOCK(gil->mutex);

int drop_requested = 0;

while (_Py_atomic_load_int_relaxed(&gil->locked)) {

unsigned long saved_switchnum = gil->switch_number;

unsigned long interval = _Py_atomic_load_ulong_relaxed(&gil->interval);

if (interval < 1) {

interval = 1;

}

int timed_out = 0;

COND_TIMED_WAIT(gil->cond, gil->mutex, interval, timed_out);

/* If we timed out and no switch occurred in the meantime, it is time

to ask the GIL-holding thread to drop it. */

if (timed_out &&

_Py_atomic_load_int_relaxed(&gil->locked) &&

gil->switch_number == saved_switchnum)

{

PyThreadState *holder_tstate =

(PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder);

if (_PyThreadState_MustExit(tstate)) {

MUTEX_UNLOCK(gil->mutex);

// gh-96387: If the loop requested a drop request in a previous

// iteration, reset the request. Otherwise, drop_gil() can

// block forever waiting for the thread which exited. Drop

// requests made by other threads are also reset: these threads

// may have to request again a drop request (iterate one more

// time).

if (drop_requested) {

_Py_unset_eval_breaker_bit(holder_tstate, _PY_GIL_DROP_REQUEST_BIT);

}

// gh-87135: hang the thread as *thread_exit() is not a safe

// API. It lacks stack unwind and local variable destruction.

_PyThreadState_HangThread(tstate);

}

assert(_PyThreadState_CheckConsistency(tstate));

_Py_set_eval_breaker_bit(holder_tstate, _PY_GIL_DROP_REQUEST_BIT);

drop_requested = 1;

}

}

#ifdef Py_GIL_DISABLED

if (!_Py_atomic_load_int_relaxed(&gil->enabled)) {

// Another thread disabled the GIL between our check above and

// now. Don't take the GIL, signal any other waiting threads, and

// return.

COND_SIGNAL(gil->cond);

MUTEX_UNLOCK(gil->mutex);

return;

}

#endif

#ifdef FORCE_SWITCHING

/* This mutex must be taken before modifying gil->last_holder:

see drop_gil(). */

MUTEX_LOCK(gil->switch_mutex);

#endif

/* We now hold the GIL */

_Py_atomic_store_int_relaxed(&gil->locked, 1);

_Py_ANNOTATE_RWLOCK_ACQUIRED(&gil->locked, /*is_write=*/1);

if (tstate != (PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) {

_Py_atomic_store_ptr_relaxed(&gil->last_holder, tstate);

++gil->switch_number;

}

#ifdef FORCE_SWITCHING

COND_SIGNAL(gil->switch_cond);

MUTEX_UNLOCK(gil->switch_mutex);

#endif

if (_PyThreadState_MustExit(tstate)) {

/* bpo-36475: If Py_Finalize() has been called and tstate is not

the thread which called Py_Finalize(), gh-87135: hang the

thread.

This code path can be reached by a daemon thread which was waiting

in take_gil() while the main thread called

wait_for_thread_shutdown() from Py_Finalize(). */

MUTEX_UNLOCK(gil->mutex);

/* tstate could be a dangling pointer, so don't pass it to

drop_gil(). */

drop_gil(interp, NULL, 1);

_PyThreadState_HangThread(tstate);

}

assert(_PyThreadState_CheckConsistency(tstate));

tstate->holds_gil = 1;

_Py_unset_eval_breaker_bit(tstate, _PY_GIL_DROP_REQUEST_BIT);

update_eval_breaker_for_thread(interp, tstate);

MUTEX_UNLOCK(gil->mutex);

errno = err;

return;

}

void _PyEval_SetSwitchInterval(unsigned long microseconds)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

struct _gil_runtime_state *gil = interp->ceval.gil;

assert(gil != NULL);

_Py_atomic_store_ulong_relaxed(&gil->interval, microseconds);

}

unsigned long _PyEval_GetSwitchInterval(void)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

struct _gil_runtime_state *gil = interp->ceval.gil;

assert(gil != NULL);

return _Py_atomic_load_ulong_relaxed(&gil->interval);

}

int

_PyEval_ThreadsInitialized(void)

{

/* XXX This is only needed for an assert in PyGILState_Ensure(),

* which currently does not work with subinterpreters.

* Thus we only use the main interpreter. */

PyInterpreterState *interp = _PyInterpreterState_Main();

if (interp == NULL) {

return 0;

}

struct _gil_runtime_state *gil = interp->ceval.gil;

return gil_created(gil);

}

// Function removed in the Python 3.13 API but kept in the stable ABI.

PyAPI_FUNC(int)

PyEval_ThreadsInitialized(void)

{

return _PyEval_ThreadsInitialized();

}

#ifndef NDEBUG

static inline int

current_thread_holds_gil(struct _gil_runtime_state *gil, PyThreadState *tstate)

{

int holds_gil = tstate->holds_gil;

// holds_gil is the source of truth; check that last_holder and gil->locked

// are consistent with it.

int locked = _Py_atomic_load_int_relaxed(&gil->locked);

int is_last_holder =

((PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) == tstate;

assert(!holds_gil || locked);

assert(!holds_gil || is_last_holder);

return holds_gil;

}

#endif

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));

#ifdef Py_GIL_DISABLED

const PyConfig *config = _PyInterpreterState_GetConfig(interp);

gil->enabled = config->enable_gil == _PyConfig_GIL_ENABLE ? INT_MAX : 0;

#endif

create_gil(gil);

assert(gil_created(gil));

interp->ceval.gil = gil;

interp->ceval.own_gil = 1;

}

void

_PyEval_InitGIL(PyThreadState *tstate, int own_gil)

{

assert(tstate->interp->ceval.gil == NULL);

if (!own_gil) {

/* The interpreter will share the main interpreter's instead. */

PyInterpreterState *main_interp = _PyInterpreterState_Main();

assert(tstate->interp != main_interp);

struct _gil_runtime_state *gil = main_interp->ceval.gil;

init_shared_gil(tstate->interp, gil);

assert(!current_thread_holds_gil(gil, tstate));

}

else {

PyThread_init_thread();

init_own_gil(tstate->interp, &tstate->interp->_gil);

}

// Lock the GIL and mark the current thread as attached.

_PyThreadState_Attach(tstate);

}

void

_PyEval_FiniGIL(PyInterpreterState *interp)

{

struct _gil_runtime_state *gil = interp->ceval.gil;

if (gil == NULL) {

/* It was already finalized (or hasn't been initialized yet). */

assert(!interp->ceval.own_gil);

return;

}

else if (!interp->ceval.own_gil) {

#ifdef Py_DEBUG

PyInterpreterState *main_interp = _PyInterpreterState_Main();

assert(main_interp != NULL && interp != main_interp);

assert(interp->ceval.gil == main_interp->ceval.gil);

#endif

interp->ceval.gil = NULL;

return;

}

if (!gil_created(gil)) {

/* First Py_InitializeFromConfig() call: the GIL doesn't exist

yet: do nothing. */

return;

}

destroy_gil(gil);

assert(!gil_created(gil));

interp->ceval.gil = NULL;

}

void

PyEval_InitThreads(void)

{

/* Do nothing: kept for backward compatibility */

}

void

_PyEval_Fini(void)

{

#ifdef Py_STATS

_Py_PrintSpecializationStats(1);

#endif

}

// Function removed in the Python 3.13 API but kept in the stable ABI.

PyAPI_FUNC(void)

PyEval_AcquireLock(void)

{

PyThreadState *tstate = _PyThreadState_GET();

_Py_EnsureTstateNotNULL(tstate);

take_gil(tstate);

}

// Function removed in the Python 3.13 API but kept in the stable ABI.

PyAPI_FUNC(void)

PyEval_ReleaseLock(void)

{

PyThreadState *tstate = _PyThreadState_GET();

/* This function must succeed when the current thread state is NULL.

We therefore avoid PyThreadState_Get() which dumps a fatal error

in debug mode. */

drop_gil(tstate->interp, tstate, 0);

}

void

_PyEval_AcquireLock(PyThreadState *tstate)

{

_Py_EnsureTstateNotNULL(tstate);

take_gil(tstate);

}

void

_PyEval_ReleaseLock(PyInterpreterState *interp,

PyThreadState *tstate,

int final_release)

{

assert(tstate != NULL);

assert(tstate->interp == interp);

drop_gil(interp, tstate, final_release);

}

void

PyEval_AcquireThread(PyThreadState *tstate)

{

_Py_EnsureTstateNotNULL(tstate);

_PyThreadState_Attach(tstate);

}

void

PyEval_ReleaseThread(PyThreadState *tstate)

{

assert(_PyThreadState_CheckConsistency(tstate));

_PyThreadState_Detach(tstate);

}

#ifdef HAVE_FORK

/* This function is called from PyOS_AfterFork_Child to re-initialize the

GIL and pending calls lock. */

PyStatus

_PyEval_ReInitThreads(PyThreadState *tstate)

{

assert(tstate->interp == _PyInterpreterState_Main());

struct _gil_runtime_state *gil = tstate->interp->ceval.gil;

if (!gil_created(gil)) {

return _PyStatus_OK();

}

recreate_gil(gil);

take_gil(tstate);

struct _pending_calls *pending = &tstate->interp->ceval.pending;

_PyMutex_at_fork_reinit(&pending->mutex);

return _PyStatus_OK();

}

#endif

PyThreadState *

PyEval_SaveThread(void)

{

PyThreadState *tstate = _PyThreadState_GET();

_PyThreadState_Detach(tstate);

return tstate;

}

void

PyEval_RestoreThread(PyThreadState *tstate)

{

#ifdef MS_WINDOWS

int err = GetLastError();

#endif

_Py_EnsureTstateNotNULL(tstate);

_PyThreadState_Attach(tstate);

#ifdef MS_WINDOWS

SetLastError(err);

#endif

}

void

_PyEval_SignalReceived(void)

{

_Py_set_eval_breaker_bit(_PyRuntime.main_tstate, _PY_SIGNALS_PENDING_BIT);

}

#ifndef Py_GIL_DISABLED

static void

signal_active_thread(PyInterpreterState *interp, uintptr_t bit)

{

struct _gil_runtime_state *gil = interp->ceval.gil;

// If a thread from the targeted interpreter is holding the GIL, signal

// that thread. Otherwise, the next thread to run from the targeted

// interpreter will have its bit set as part of taking the GIL.

MUTEX_LOCK(gil->mutex);

if (_Py_atomic_load_int_relaxed(&gil->locked)) {

PyThreadState *holder = (PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder);

if (holder->interp == interp) {

_Py_set_eval_breaker_bit(holder, bit);

}

}

MUTEX_UNLOCK(gil->mutex);

}

#endif

/* Mechanism whereby asynchronously executing callbacks (e.g. UNIX

signal handlers or Mac I/O completion routines) can schedule calls

to a function to be called synchronously.

The synchronous function is called with one void* argument.

It should return 0 for success or -1 for failure -- failure should

be accompanied by an exception.

If registry succeeds, the registry function returns 0; if it fails

(e.g. due to too many pending calls) it returns -1 (without setting

an exception condition).

Note that because registry may occur from within signal handlers,

or other asynchronous events, calling malloc() is unsafe!

Any thread can schedule pending calls, but only the main thread

will execute them.

There is no facility to schedule calls to a particular thread, but

that should be easy to change, should that ever be required. In

that case, the static variables here should go into the python

threadstate.

*/

/* Push one item onto the queue while holding the lock. */

static int

_push_pending_call(struct _pending_calls *pending,

_Py_pending_call_func func, void *arg, int flags)

{

if (pending->npending == pending->max) {

return _Py_ADD_PENDING_FULL;

}

assert(pending->npending < pending->max);

int i = pending->next;

assert(pending->calls[i].func == NULL);

pending->calls[i].func = func;

pending->calls[i].arg = arg;

pending->calls[i].flags = flags;

assert(pending->npending < PENDINGCALLSARRAYSIZE);

_Py_atomic_add_int32(&pending->npending, 1);

pending->next = (i + 1) % PENDINGCALLSARRAYSIZE;

assert(pending->next != pending->first

|| pending->npending == pending->max);

return _Py_ADD_PENDING_SUCCESS;

}

static int

_next_pending_call(struct _pending_calls *pending,

int (**func)(void *), void **arg, int *flags)

{

int i = pending->first;

if (pending->npending == 0) {

/* Queue empty */

assert(i == pending->next);

assert(pending->calls[i].func == NULL);

return -1;

}

*func = pending->calls[i].func;

*arg = pending->calls[i].arg;

*flags = pending->calls[i].flags;

return i;

}

/* Pop one item off the queue while holding the lock. */

static void

_pop_pending_call(struct _pending_calls *pending,

int (**func)(void *), void **arg, int *flags)

{

int i = _next_pending_call(pending, func, arg, flags);

if (i >= 0) {

pending->calls[i] = (struct _pending_call){0};

pending->first = (i + 1) % PENDINGCALLSARRAYSIZE;

assert(pending->npending > 0);

_Py_atomic_add_int32(&pending->npending, -1);

}

}

/* This implementation is thread-safe. It allows

scheduling to be made from any thread, and even from an executing

callback.

*/

_Py_add_pending_call_result

_PyEval_AddPendingCall(PyInterpreterState *interp,

_Py_pending_call_func func, void *arg, int flags)

{

struct _pending_calls *pending = &interp->ceval.pending;

int main_only = (flags & _Py_PENDING_MAINTHREADONLY) != 0;

if (main_only) {

/* The main thread only exists in the main interpreter. */

assert(_Py_IsMainInterpreter(interp));

pending = &_PyRuntime.ceval.pending_mainthread;

}

PyMutex_Lock(&pending->mutex);

_Py_add_pending_call_result result =

_push_pending_call(pending, func, arg, flags);

PyMutex_Unlock(&pending->mutex);

if (main_only) {

_Py_set_eval_breaker_bit(_PyRuntime.main_tstate, _PY_CALLS_TO_DO_BIT);

}

else {

#ifdef Py_GIL_DISABLED

_Py_set_eval_breaker_bit_all(interp, _PY_CALLS_TO_DO_BIT);

#else

signal_active_thread(interp, _PY_CALLS_TO_DO_BIT);

#endif

}

return result;

}

int

Py_AddPendingCall(_Py_pending_call_func func, void *arg)

{

/* Legacy users of this API will continue to target the main thread

(of the main interpreter). */

PyInterpreterState *interp = _PyInterpreterState_Main();

_Py_add_pending_call_result r =

_PyEval_AddPendingCall(interp, func, arg, _Py_PENDING_MAINTHREADONLY);

if (r == _Py_ADD_PENDING_FULL) {

return -1;

}

else {

assert(r == _Py_ADD_PENDING_SUCCESS);

return 0;

}

}

static int

handle_signals(PyThreadState *tstate)

{

assert(_PyThreadState_CheckConsistency(tstate));

_Py_unset_eval_breaker_bit(tstate, _PY_SIGNALS_PENDING_BIT);

if (!_Py_ThreadCanHandleSignals(tstate->interp)) {

return 0;

}

if (_PyErr_CheckSignalsTstate(tstate) < 0) {

/* On failure, re-schedule a call to handle_signals(). */

_Py_set_eval_breaker_bit(tstate, _PY_SIGNALS_PENDING_BIT);

return -1;

}

return 0;

}

static int

_make_pending_calls(struct _pending_calls *pending, int32_t *p_npending)

{

int res = 0;

int32_t npending = -1;

assert(sizeof(pending->max) <= sizeof(size_t)

&& ((size_t)pending->max) <= Py_ARRAY_LENGTH(pending->calls));

int32_t maxloop = pending->maxloop;

if (maxloop == 0) {

maxloop = pending->max;

}

assert(maxloop > 0 && maxloop <= pending->max);

/* perform a bounded number of calls, in case of recursion */

for (int i=0; i<maxloop; i++) {

_Py_pending_call_func func = NULL;

void *arg = NULL;

int flags = 0;

/* pop one item off the queue while holding the lock */

PyMutex_Lock(&pending->mutex);

_pop_pending_call(pending, &func, &arg, &flags);

npending = pending->npending;

PyMutex_Unlock(&pending->mutex);

/* Check if there are any more pending calls. */

if (func == NULL) {

assert(npending == 0);

break;

}

/* having released the lock, perform the callback */

res = func(arg);

if ((flags & _Py_PENDING_RAWFREE) && arg != NULL) {

PyMem_RawFree(arg);

}

if (res != 0) {

res = -1;

goto finally;

}

}

finally:

*p_npending = npending;

return res;

}

static void

signal_pending_calls(PyThreadState *tstate, PyInterpreterState *interp)

{

#ifdef Py_GIL_DISABLED

_Py_set_eval_breaker_bit_all(interp, _PY_CALLS_TO_DO_BIT);

#else

_Py_set_eval_breaker_bit(tstate, _PY_CALLS_TO_DO_BIT);

#endif

}

static void

unsignal_pending_calls(PyThreadState *tstate, PyInterpreterState *interp)

{

#ifdef Py_GIL_DISABLED

_Py_unset_eval_breaker_bit_all(interp, _PY_CALLS_TO_DO_BIT);

#else

_Py_unset_eval_breaker_bit(tstate, _PY_CALLS_TO_DO_BIT);

#endif

}

static void

clear_pending_handling_thread(struct _pending_calls *pending)

{

FT_MUTEX_LOCK(&pending->mutex);

pending->handling_thread = NULL;

FT_MUTEX_UNLOCK(&pending->mutex);

}

static int

make_pending_calls(PyThreadState *tstate)

{

PyInterpreterState *interp = tstate->interp;

struct _pending_calls *pending = &interp->ceval.pending;

struct _pending_calls *pending_main = &_PyRuntime.ceval.pending_mainthread;

/* Only one thread (per interpreter) may run the pending calls

at once. In the same way, we don't do recursive pending calls. */

PyMutex_Lock(&pending->mutex);

if (pending->handling_thread != NULL) {

/* A pending call was added after another thread was already

handling the pending calls (and had already "unsignaled").

Once that thread is done, it may have taken care of all the

pending calls, or there might be some still waiting.

To avoid all threads constantly stopping on the eval breaker,

we clear the bit for this thread and make sure it is set

for the thread currently handling the pending call. */

_Py_set_eval_breaker_bit(pending->handling_thread, _PY_CALLS_TO_DO_BIT);

_Py_unset_eval_breaker_bit(tstate, _PY_CALLS_TO_DO_BIT);

PyMutex_Unlock(&pending->mutex);

return 0;

}

pending->handling_thread = tstate;

PyMutex_Unlock(&pending->mutex);

/* unsignal before starting to call callbacks, so that any callback

added in-between re-signals */

unsignal_pending_calls(tstate, interp);

int32_t npending;

if (_make_pending_calls(pending, &npending) != 0) {

clear_pending_handling_thread(pending);

/* There might not be more calls to make, but we play it safe. */

signal_pending_calls(tstate, interp);

return -1;

}

if (npending > 0) {

/* We hit pending->maxloop. */

signal_pending_calls(tstate, interp);

}

if (_Py_IsMainThread() && _Py_IsMainInterpreter(interp)) {

if (_make_pending_calls(pending_main, &npending) != 0) {

clear_pending_handling_thread(pending);

/* There might not be more calls to make, but we play it safe. */

signal_pending_calls(tstate, interp);

return -1;

}

if (npending > 0) {

/* We hit pending_main->maxloop. */

signal_pending_calls(tstate, interp);

}

}

clear_pending_handling_thread(pending);

return 0;

}

void

_Py_set_eval_breaker_bit_all(PyInterpreterState *interp, uintptr_t bit)

{

_Py_FOR_EACH_TSTATE_BEGIN(interp, tstate) {

_Py_set_eval_breaker_bit(tstate, bit);

}

_Py_FOR_EACH_TSTATE_END(interp);

}

void

_Py_unset_eval_breaker_bit_all(PyInterpreterState *interp, uintptr_t bit)

{

_Py_FOR_EACH_TSTATE_BEGIN(interp, tstate) {

_Py_unset_eval_breaker_bit(tstate, bit);

}

_Py_FOR_EACH_TSTATE_END(interp);

}

void

_Py_FinishPendingCalls(PyThreadState *tstate)

{

_Py_AssertHoldsTstate();

assert(_PyThreadState_CheckConsistency(tstate));

struct _pending_calls *pending = &tstate->interp->ceval.pending;

struct _pending_calls *pending_main =