Update 2025-04-13_16:25:39
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/* -*- indent-tabs-mode: nil; tab-width: 4; -*- */
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/**
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* Implementation of the ThreadState destructors.
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*
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* Format with:
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* clang-format -i --style=file src/greenlet/greenlet.c
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*
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*
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* Fix missing braces with:
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* clang-tidy src/greenlet/greenlet.c -fix -checks="readability-braces-around-statements"
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*/
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#ifndef T_THREADSTATE_DESTROY
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#define T_THREADSTATE_DESTROY
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#include "TGreenlet.hpp"
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#include "greenlet_thread_support.hpp"
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#include "greenlet_cpython_add_pending.hpp"
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#include "greenlet_compiler_compat.hpp"
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#include "TGreenletGlobals.cpp"
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#include "TThreadState.hpp"
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#include "TThreadStateCreator.hpp"
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namespace greenlet {
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extern "C" {
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struct ThreadState_DestroyNoGIL
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{
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/**
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This function uses the same lock that the PendingCallback does
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*/
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static void
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MarkGreenletDeadAndQueueCleanup(ThreadState* const state)
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{
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#if GREENLET_BROKEN_THREAD_LOCAL_CLEANUP_JUST_LEAK
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return;
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#endif
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// We are *NOT* holding the GIL. Our thread is in the middle
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// of its death throes and the Python thread state is already
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// gone so we can't use most Python APIs. One that is safe is
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// ``Py_AddPendingCall``, unless the interpreter itself has
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// been torn down. There is a limited number of calls that can
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// be queued: 32 (NPENDINGCALLS) in CPython 3.10, so we
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// coalesce these calls using our own queue.
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if (!MarkGreenletDeadIfNeeded(state)) {
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// No state, or no greenlet
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return;
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}
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// XXX: Because we don't have the GIL, this is a race condition.
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if (!PyInterpreterState_Head()) {
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// We have to leak the thread state, if the
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// interpreter has shut down when we're getting
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// deallocated, we can't run the cleanup code that
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// deleting it would imply.
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return;
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}
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AddToCleanupQueue(state);
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}
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private:
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// If the state has an allocated main greenlet:
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// - mark the greenlet as dead by disassociating it from the state;
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// - return 1
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// Otherwise, return 0.
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static bool
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MarkGreenletDeadIfNeeded(ThreadState* const state)
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{
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if (state && state->has_main_greenlet()) {
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// mark the thread as dead ASAP.
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// this is racy! If we try to throw or switch to a
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// greenlet from this thread from some other thread before
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// we clear the state pointer, it won't realize the state
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// is dead which can crash the process.
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PyGreenlet* p(state->borrow_main_greenlet().borrow());
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assert(p->pimpl->thread_state() == state || p->pimpl->thread_state() == nullptr);
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dynamic_cast<MainGreenlet*>(p->pimpl)->thread_state(nullptr);
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return true;
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}
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return false;
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}
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static void
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AddToCleanupQueue(ThreadState* const state)
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{
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assert(state && state->has_main_greenlet());
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// NOTE: Because we're not holding the GIL here, some other
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// Python thread could run and call ``os.fork()``, which would
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// be bad if that happened while we are holding the cleanup
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// lock (it wouldn't function in the child process).
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// Make a best effort to try to keep the duration we hold the
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// lock short.
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// TODO: On platforms that support it, use ``pthread_atfork`` to
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// drop this lock.
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LockGuard cleanup_lock(*mod_globs->thread_states_to_destroy_lock);
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mod_globs->queue_to_destroy(state);
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if (mod_globs->thread_states_to_destroy.size() == 1) {
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// We added the first item to the queue. We need to schedule
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// the cleanup.
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// A size greater than 1 means that we have already added the pending call,
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// and in fact, it may be executing now.
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// If it is executing, our lock makes sure that it will see the item we just added
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// to the queue on its next iteration (after we release the lock)
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//
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// A size of 1 means there is no pending call, OR the pending call is
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// currently executing, has dropped the lock, and is deleting the last item
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// from the queue; its next iteration will go ahead and delete the item we just added.
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// And the pending call we schedule here will have no work to do.
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int result = AddPendingCall(
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PendingCallback_DestroyQueueWithGIL,
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nullptr);
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if (result < 0) {
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// Hmm, what can we do here?
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fprintf(stderr,
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"greenlet: WARNING: failed in call to Py_AddPendingCall; "
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"expect a memory leak.\n");
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}
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}
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}
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static int
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PendingCallback_DestroyQueueWithGIL(void* UNUSED(arg))
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{
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// We're holding the GIL here, so no Python code should be able to
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// run to call ``os.fork()``.
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while (1) {
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ThreadState* to_destroy;
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{
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LockGuard cleanup_lock(*mod_globs->thread_states_to_destroy_lock);
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if (mod_globs->thread_states_to_destroy.empty()) {
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break;
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}
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to_destroy = mod_globs->take_next_to_destroy();
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}
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assert(to_destroy);
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assert(to_destroy->has_main_greenlet());
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// Drop the lock while we do the actual deletion.
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// This allows other calls to MarkGreenletDeadAndQueueCleanup
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// to enter and add to our queue.
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DestroyOneWithGIL(to_destroy);
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}
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return 0;
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}
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static void
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DestroyOneWithGIL(const ThreadState* const state)
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{
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// Holding the GIL.
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// Passed a non-shared pointer to the actual thread state.
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// state -> main greenlet
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assert(state->has_main_greenlet());
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PyGreenlet* main(state->borrow_main_greenlet());
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// When we need to do cross-thread operations, we check this.
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// A NULL value means the thread died some time ago.
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// We do this here, rather than in a Python dealloc function
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// for the greenlet, in case there's still a reference out
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// there.
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dynamic_cast<MainGreenlet*>(main->pimpl)->thread_state(nullptr);
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delete state; // Deleting this runs the destructor, DECREFs the main greenlet.
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}
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// ensure this is actually defined.
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static_assert(GREENLET_BROKEN_PY_ADD_PENDING == 1 || GREENLET_BROKEN_PY_ADD_PENDING == 0,
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"GREENLET_BROKEN_PY_ADD_PENDING not defined correctly.");
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#if GREENLET_BROKEN_PY_ADD_PENDING
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static int _push_pending_call(struct _pending_calls *pending,
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int (*func)(void *), void *arg)
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{
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int i = pending->last;
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int j = (i + 1) % NPENDINGCALLS;
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if (j == pending->first) {
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return -1; /* Queue full */
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}
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pending->calls[i].func = func;
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pending->calls[i].arg = arg;
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pending->last = j;
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return 0;
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}
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static int AddPendingCall(int (*func)(void *), void *arg)
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{
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_PyRuntimeState *runtime = &_PyRuntime;
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if (!runtime) {
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// obviously impossible
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return 0;
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}
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struct _pending_calls *pending = &runtime->ceval.pending;
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if (!pending->lock) {
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return 0;
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}
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int result = 0;
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PyThread_acquire_lock(pending->lock, WAIT_LOCK);
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if (!pending->finishing) {
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result = _push_pending_call(pending, func, arg);
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}
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PyThread_release_lock(pending->lock);
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SIGNAL_PENDING_CALLS(&runtime->ceval);
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return result;
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}
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#else
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// Python < 3.8 or >= 3.9
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static int AddPendingCall(int (*func)(void*), void* arg)
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{
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// If the interpreter is in the middle of finalizing, we can't add a
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// pending call. Trying to do so will end up in a SIGSEGV, as
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// Py_AddPendingCall will not be able to get the interpreter and will
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// try to dereference a NULL pointer. It's possible this can still
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// segfault if we happen to get context switched, and maybe we should
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// just always implement our own AddPendingCall, but I'd like to see if
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// this works first
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#if GREENLET_PY313
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if (Py_IsFinalizing()) {
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#else
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if (_Py_IsFinalizing()) {
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#endif
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#ifdef GREENLET_DEBUG
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// No need to log in the general case. Yes, we'll leak,
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// but we're shutting down so it should be ok.
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fprintf(stderr,
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"greenlet: WARNING: Interpreter is finalizing. Ignoring "
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"call to Py_AddPendingCall; \n");
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#endif
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return 0;
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}
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return Py_AddPendingCall(func, arg);
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}
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#endif
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};
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};
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}; // namespace greenlet
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// The intent when GET_THREAD_STATE() is needed multiple times in a
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// function is to take a reference to its return value in a local
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// variable, to avoid the thread-local indirection. On some platforms
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// (macOS), accessing a thread-local involves a function call (plus an
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// initial function call in each function that uses a thread local);
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// in contrast, static volatile variables are at some pre-computed
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// offset.
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typedef greenlet::ThreadStateCreator<greenlet::ThreadState_DestroyNoGIL::MarkGreenletDeadAndQueueCleanup> ThreadStateCreator;
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static thread_local ThreadStateCreator g_thread_state_global;
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#define GET_THREAD_STATE() g_thread_state_global
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#endif //T_THREADSTATE_DESTROY
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