1 files changed, 100 insertions, 0 deletions
diff --git a/Python/critical_section.c b/Python/critical_section.c
new file mode 100644
index 00000000000..2214d80eeb2
--- /dev/null
+++ b/Python/critical_section.c
@@ -0,0 +1,100 @@
+#include "Python.h"
+
+#include "pycore_lock.h"
+#include "pycore_critical_section.h"
+
+static_assert(_Alignof(_PyCriticalSection) >= 4,
+              "critical section must be aligned to at least 4 bytes");
+
+void
+_PyCriticalSection_BeginSlow(_PyCriticalSection *c, PyMutex *m)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+    c->mutex = NULL;
+    c->prev = (uintptr_t)tstate->critical_section;
+    tstate->critical_section = (uintptr_t)c;
+
+    _PyMutex_LockSlow(m);
+    c->mutex = m;
+}
+
+void
+_PyCriticalSection2_BeginSlow(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
+                              int is_m1_locked)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+    c->base.mutex = NULL;
+    c->mutex2 = NULL;
+    c->base.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->base.mutex = m1;
+    c->mutex2 = m2;
+}
+
+static _PyCriticalSection *
+untag_critical_section(uintptr_t tag)
+{
+    return (_PyCriticalSection *)(tag & ~_Py_CRITICAL_SECTION_MASK);
+}
+
+// Release all locks held by critical sections. This is called by
+// _PyThreadState_Detach.
+void
+_PyCriticalSection_SuspendAll(PyThreadState *tstate)
+{
+    uintptr_t *tagptr = &tstate->critical_section;
+    while (_PyCriticalSection_IsActive(*tagptr)) {
+        _PyCriticalSection *c = untag_critical_section(*tagptr);
+
+        if (c->mutex) {
+            PyMutex_Unlock(c->mutex);
+            if ((*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
+                _PyCriticalSection2 *c2 = (_PyCriticalSection2 *)c;
+                if (c2->mutex2) {
+                    PyMutex_Unlock(c2->mutex2);
+                }
+            }
+        }
+
+        *tagptr |= _Py_CRITICAL_SECTION_INACTIVE;
+        tagptr = &c->prev;
+    }
+}
+
+void
+_PyCriticalSection_Resume(PyThreadState *tstate)
+{
+    uintptr_t p = tstate->critical_section;
+    _PyCriticalSection *c = untag_critical_section(p);
+    assert(!_PyCriticalSection_IsActive(p));
+
+    PyMutex *m1 = c->mutex;
+    c->mutex = NULL;
+
+    PyMutex *m2 = NULL;
+    _PyCriticalSection2 *c2 = NULL;
+    if ((p & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
+        c2 = (_PyCriticalSection2 *)c;
+        m2 = c2->mutex2;
+        c2->mutex2 = NULL;
+    }
+
+    if (m1) {
+        PyMutex_Lock(m1);
+    }
+    if (m2) {
+        PyMutex_Lock(m2);
+    }
+
+    c->mutex = m1;
+    if (m2) {
+        c2->mutex2 = m2;
+    }
+
+    tstate->critical_section &= ~_Py_CRITICAL_SECTION_INACTIVE;
+}