gh-116738: Make _csv module thread-safe

Include/internal/pycore_pyatomic_ft_wrappers.h

@@ -40,6 +40,7 @@ extern "C" {
     _Py_atomic_store_ssize_relaxed(&value, new_value)
 #define FT_ATOMIC_STORE_UINT8_RELAXED(value, new_value) \
     _Py_atomic_store_uint8_relaxed(&value, new_value)
+#define FT_ATOMIC_LOAD_INT32(value) _Py_atomic_load_int32(&value)
 
 #else
 #define FT_ATOMIC_LOAD_PTR(value) value
@@ -53,6 +54,7 @@ extern "C" {
 #define FT_ATOMIC_STORE_UINTPTR_RELEASE(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_SSIZE_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_UINT8_RELAXED(value, new_value) value = new_value
+#define FT_ATOMIC_LOAD_INT32(value) value
 
 #endif
 

Modules/_csv.c

@@ -14,6 +14,7 @@ module instead.
 #endif
 
 #include "Python.h"
+#include "pycore_pyatomic_ft_wrappers.h"  // FT_ATOMIC_LOAD_INT32
 
 #include <stddef.h>               // offsetof()
 #include <stdbool.h>
@@ -34,7 +35,7 @@ typedef struct {
     PyTypeObject *dialect_type;
     PyTypeObject *reader_type;
     PyTypeObject *writer_type;
-    long field_limit;   /* max parsed field size */
+    int32_t field_limit;   /* max parsed field size */
     PyObject *str_write;
 } _csvstate;
 
@@ -702,10 +703,11 @@ parse_grow_buff(ReaderObj *self)
 static int
 parse_add_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
 {
-    if (self->field_len >= module_state->field_limit) {
+    uint32_t field_limit = FT_ATOMIC_LOAD_INT32(module_state->field_limit);
+    if (self->field_len >= field_limit) {
         PyErr_Format(module_state->error_obj,
                      "field larger than field limit (%ld)",
-                     module_state->field_limit);
+                     field_limit);
         return -1;
     }
     if (self->field_len == self->field_size && !parse_grow_buff(self))
@@ -1571,6 +1573,7 @@ csv_register_dialect(PyObject *module, PyObject *args, PyObject *kwargs)
     PyObject *name_obj, *dialect_obj = NULL;
     _csvstate *module_state = get_csv_state(module);
     PyObject *dialect;
+    int res;
 
     if (!PyArg_UnpackTuple(args, "", 1, 2, &name_obj, &dialect_obj))
         return NULL;
@@ -1582,7 +1585,8 @@ csv_register_dialect(PyObject *module, PyObject *args, PyObject *kwargs)
     dialect = _call_dialect(module_state, dialect_obj, kwargs);
     if (dialect == NULL)
         return NULL;
-    if (PyDict_SetItem(module_state->dialects, name_obj, dialect) < 0) {
+    res = PyDict_SetItem(module_state->dialects, name_obj, dialect);
+    if (res < 0) {
         Py_DECREF(dialect);
         return NULL;
     }
@@ -1635,6 +1639,7 @@ _csv_get_dialect_impl(PyObject *module, PyObject *name)
 }
 
 /*[clinic input]
+@critical_section
 _csv.field_size_limit
 
     new_limit: object = NULL
@@ -1649,10 +1654,10 @@ the old limit is returned
 
 static PyObject *
 _csv_field_size_limit_impl(PyObject *module, PyObject *new_limit)
-/*[clinic end generated code: output=f2799ecd908e250b input=cec70e9226406435]*/
+/*[clinic end generated code: output=f2799ecd908e250b input=3e49d42e37a7d449]*/
 {
     _csvstate *module_state = get_csv_state(module);
-    long old_limit = module_state->field_limit;
+    int32_t old_limit = module_state->field_limit;
     if (new_limit != NULL) {
         if (!PyLong_CheckExact(new_limit)) {
             PyErr_Format(PyExc_TypeError,