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GeezerVison is showing github.com — cpython/Python/critical_section.c at 3.14 · python/cpython

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critical_section.c

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#include "Python.h"
#include "pycore_critical_section.h"
#include "pycore_interp.h"
#include "pycore_lock.h"
#ifdef Py_GIL_DISABLED
static_assert(_Alignof(PyCriticalSection) >= 4,
"critical section must be aligned to at least 4 bytes");
#endif
#ifdef Py_GIL_DISABLED
static PyCriticalSection *
untag_critical_section(uintptr_t tag)
{
return (PyCriticalSection *)(tag & ~_Py_CRITICAL_SECTION_MASK);
}
#endif
void
_PyCriticalSection_BeginSlow(PyCriticalSection *c, PyMutex *m)
{
#ifdef Py_GIL_DISABLED
PyThreadState *tstate = _PyThreadState_GET();
// As an optimisation for locking the same object recursively, skip
// locking if the mutex is currently locked by the top-most critical
// section.
// If the top-most critical section is a two-mutex critical section,
// then locking is skipped if either mutex is m.
if (tstate->critical_section) {
PyCriticalSection *prev = untag_critical_section(tstate->critical_section);
if (prev->_cs_mutex == m) {
c->_cs_mutex = NULL;
c->_cs_prev = 0;
return;
}
if (tstate->critical_section & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
PyCriticalSection2 *prev2 = (PyCriticalSection2 *)
untag_critical_section(tstate->critical_section);
if (prev2->_cs_mutex2 == m) {
c->_cs_mutex = NULL;
c->_cs_prev = 0;
return;
}
}
}
// If the world is stopped, we don't need to acquire the lock because
// there are no other threads that could be accessing the object.
// Without this check, acquiring a critical section while the world is
// stopped could lead to a deadlock.
if (tstate->interp->stoptheworld.world_stopped) {
c->_cs_mutex = NULL;
c->_cs_prev = 0;
return;
}
c->_cs_mutex = NULL;
c->_cs_prev = (uintptr_t)tstate->critical_section;
tstate->critical_section = (uintptr_t)c;
PyMutex_Lock(m);
c->_cs_mutex = m;
#endif
}
void
_PyCriticalSection2_BeginSlow(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
int is_m1_locked)
{
#ifdef Py_GIL_DISABLED
PyThreadState *tstate = _PyThreadState_GET();
if (tstate->interp->stoptheworld.world_stopped) {
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = 0;
return;
}
// Same optimization as in _PyCriticalSection_BeginSlow: skip locking when
// recursively acquiring the same locks.
if (tstate->critical_section &&
tstate->critical_section & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
PyCriticalSection2 *prev2 = (PyCriticalSection2 *)
untag_critical_section(tstate->critical_section);
assert((uintptr_t)m1 < (uintptr_t)m2);
assert((uintptr_t)prev2->_cs_base._cs_mutex <
(uintptr_t)prev2->_cs_mutex2);
if (prev2->_cs_base._cs_mutex == m1 && prev2->_cs_mutex2 == m2) {
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = 0;
return;
}
}
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = tstate->critical_section;
tstate->critical_section = (uintptr_t)c | _Py_CRITICAL_SECTION_TWO_MUTEXES;
if (!is_m1_locked) {
PyMutex_Lock(m1);
}
PyMutex_Lock(m2);
c->_cs_base._cs_mutex = m1;
c->_cs_mutex2 = m2;
#endif
}
// Release all locks held by critical sections. This is called by
// _PyThreadState_Detach.
void
_PyCriticalSection_SuspendAll(PyThreadState *tstate)
{
#ifdef Py_GIL_DISABLED
uintptr_t *tagptr = &tstate->critical_section;
while (_PyCriticalSection_IsActive(*tagptr)) {
PyCriticalSection *c = untag_critical_section(*tagptr);
if (c->_cs_mutex) {
PyMutex_Unlock(c->_cs_mutex);
if ((*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
PyCriticalSection2 *c2 = (PyCriticalSection2 *)c;
if (c2->_cs_mutex2) {
PyMutex_Unlock(c2->_cs_mutex2);
}
}
}
*tagptr |= _Py_CRITICAL_SECTION_INACTIVE;
tagptr = &c->_cs_prev;
}
#endif
}
void
_PyCriticalSection_Resume(PyThreadState *tstate)
{
#ifdef Py_GIL_DISABLED
uintptr_t p = tstate->critical_section;
PyCriticalSection *c = untag_critical_section(p);
assert(!_PyCriticalSection_IsActive(p));
PyMutex *m1 = c->_cs_mutex;
c->_cs_mutex = NULL;
PyMutex *m2 = NULL;
PyCriticalSection2 *c2 = NULL;
if ((p & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
c2 = (PyCriticalSection2 *)c;
m2 = c2->_cs_mutex2;
c2->_cs_mutex2 = NULL;
}
if (m1) {
PyMutex_Lock(m1);
}
if (m2) {
PyMutex_Lock(m2);
}
c->_cs_mutex = m1;
if (m2) {
c2->_cs_mutex2 = m2;
}
tstate->critical_section &= ~_Py_CRITICAL_SECTION_INACTIVE;
#endif
}
#undef PyCriticalSection_Begin
void
PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection_Begin(c, op);
#endif
}
#undef PyCriticalSection_BeginMutex
void
PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection_BeginMutex(c, m);
#endif
}
#undef PyCriticalSection_End
void
PyCriticalSection_End(PyCriticalSection *c)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection_End(c);
#endif
}
#undef PyCriticalSection2_Begin
void
PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection2_Begin(c, a, b);
#endif
}
#undef PyCriticalSection2_BeginMutex
void
PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection2_BeginMutex(c, m1, m2);
#endif
}
#undef PyCriticalSection2_End
void
PyCriticalSection2_End(PyCriticalSection2 *c)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection2_End(c);
#endif
}
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