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31c90d5838
Critical sections are helpers to replace the global interpreter lock with finer grained locking. They provide similar guarantees to the GIL and avoid the deadlock risk that plain locking involves. Critical sections are implicitly ended whenever the GIL would be released. They are resumed when the GIL would be acquired. Nested critical sections behave as if the sections were interleaved.
100 lines
2.5 KiB
C
100 lines
2.5 KiB
C
#include "Python.h"
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#include "pycore_lock.h"
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#include "pycore_critical_section.h"
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static_assert(_Alignof(_PyCriticalSection) >= 4,
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"critical section must be aligned to at least 4 bytes");
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void
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_PyCriticalSection_BeginSlow(_PyCriticalSection *c, PyMutex *m)
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{
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PyThreadState *tstate = _PyThreadState_GET();
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c->mutex = NULL;
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c->prev = (uintptr_t)tstate->critical_section;
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tstate->critical_section = (uintptr_t)c;
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_PyMutex_LockSlow(m);
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c->mutex = m;
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}
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void
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_PyCriticalSection2_BeginSlow(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
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int is_m1_locked)
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{
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PyThreadState *tstate = _PyThreadState_GET();
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c->base.mutex = NULL;
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c->mutex2 = NULL;
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c->base.prev = tstate->critical_section;
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tstate->critical_section = (uintptr_t)c | _Py_CRITICAL_SECTION_TWO_MUTEXES;
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if (!is_m1_locked) {
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PyMutex_Lock(m1);
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}
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PyMutex_Lock(m2);
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c->base.mutex = m1;
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c->mutex2 = m2;
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}
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static _PyCriticalSection *
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untag_critical_section(uintptr_t tag)
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{
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return (_PyCriticalSection *)(tag & ~_Py_CRITICAL_SECTION_MASK);
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}
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// Release all locks held by critical sections. This is called by
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// _PyThreadState_Detach.
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void
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_PyCriticalSection_SuspendAll(PyThreadState *tstate)
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{
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uintptr_t *tagptr = &tstate->critical_section;
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while (_PyCriticalSection_IsActive(*tagptr)) {
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_PyCriticalSection *c = untag_critical_section(*tagptr);
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if (c->mutex) {
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PyMutex_Unlock(c->mutex);
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if ((*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
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_PyCriticalSection2 *c2 = (_PyCriticalSection2 *)c;
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if (c2->mutex2) {
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PyMutex_Unlock(c2->mutex2);
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}
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}
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}
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*tagptr |= _Py_CRITICAL_SECTION_INACTIVE;
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tagptr = &c->prev;
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}
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}
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void
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_PyCriticalSection_Resume(PyThreadState *tstate)
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{
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uintptr_t p = tstate->critical_section;
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_PyCriticalSection *c = untag_critical_section(p);
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assert(!_PyCriticalSection_IsActive(p));
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PyMutex *m1 = c->mutex;
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c->mutex = NULL;
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PyMutex *m2 = NULL;
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_PyCriticalSection2 *c2 = NULL;
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if ((p & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
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c2 = (_PyCriticalSection2 *)c;
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m2 = c2->mutex2;
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c2->mutex2 = NULL;
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}
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if (m1) {
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PyMutex_Lock(m1);
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}
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if (m2) {
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PyMutex_Lock(m2);
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}
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c->mutex = m1;
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if (m2) {
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c2->mutex2 = m2;
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}
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tstate->critical_section &= ~_Py_CRITICAL_SECTION_INACTIVE;
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}
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