Replace critical sections with atomic operations

Author: yoney

Include/internal/pycore_pyatomic_ft_wrappers.h

@@ -77,6 +77,10 @@ extern "C" {
     _Py_atomic_store_ushort_relaxed(&value, new_value)
 #define FT_ATOMIC_LOAD_USHORT_RELAXED(value) \
     _Py_atomic_load_ushort_relaxed(&value)
+#define FT_ATOMIC_LOAD_INT(value) \
+    _Py_atomic_load_int(&value)
+#define FT_ATOMIC_STORE_INT(value, new_value) \
+    _Py_atomic_store_int(&value, new_value)
 #define FT_ATOMIC_STORE_INT_RELAXED(value, new_value) \
     _Py_atomic_store_int_relaxed(&value, new_value)
 #define FT_ATOMIC_LOAD_INT_RELAXED(value) \
@@ -144,6 +148,8 @@ extern "C" {
 #define FT_ATOMIC_STORE_SHORT_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_LOAD_USHORT_RELAXED(value) value
 #define FT_ATOMIC_STORE_USHORT_RELAXED(value, new_value) value = new_value
+#define FT_ATOMIC_LOAD_INT(value) value
+#define FT_ATOMIC_STORE_INT(value, new_value) value = new_value
 #define FT_ATOMIC_LOAD_INT_RELAXED(value) value
 #define FT_ATOMIC_STORE_INT_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_LOAD_UINT_RELAXED(value) value

Misc/NEWS.d/next/Core_and_Builtins/2025-11-25-13-13-34.gh-issue-116738.MnZRdV.rst

@@ -0,0 +1,2 @@
+Fix thread safety issue with :mod:`re` scanner objects in free-threaded
+builds.

Modules/_sre/sre.c

@@ -2841,28 +2841,25 @@ scanner_dealloc(PyObject *self)
 static int
 scanner_begin(ScannerObject* self)
 {
-    int result;
-    Py_BEGIN_CRITICAL_SECTION(self);
-    if (self->executing) {
+#ifdef Py_GIL_DISABLED
+    int was_executing = _Py_atomic_exchange_int(&self->executing, 1);
+#else
+    int was_executing = self->executing;
+    self->executing = 1;
+#endif
+    if (was_executing) {
         PyErr_SetString(PyExc_ValueError,
                         "regular expression scanner already executing");
-        result = 0;
-    }
-    else {
-        self->executing = 1;
-        result = 1;
+        return 0;
     }
-    Py_END_CRITICAL_SECTION();
-    return result;
+    return 1;
 }
 
 static void
 scanner_end(ScannerObject* self)
 {
-    Py_BEGIN_CRITICAL_SECTION(self);
-    assert(self->executing);
-    self->executing = 0;
-    Py_END_CRITICAL_SECTION();
+    assert(FT_ATOMIC_LOAD_INT_RELAXED(self->executing));
+    FT_ATOMIC_STORE_INT(self->executing, 0);
 }
 
 /*[clinic input]