Fix __repr__ race (Free-Threaded)

CHANGES/1328.bugfix.rst

@@ -0,0 +1,2 @@
+Fixed race when calling for a string representation of a ``MultiDict`` object.
+-- by :user:`Vizonex`

multidict/_multilib/hashtable.h

@@ -1769,6 +1769,7 @@ md_repr(MultiDictObject *md, PyObject *name, bool show_keys, bool show_values)
     PyObject *key = NULL;
     PyObject *value = NULL;
 
+    Py_BEGIN_CRITICAL_SECTION(md);
     bool comma = false;
     uint64_t version = md->version;
 
@@ -1850,6 +1851,7 @@ md_repr(MultiDictObject *md, PyObject *name, bool show_keys, bool show_values)
     Py_CLEAR(key);
     Py_CLEAR(value);
     PyUnicodeWriter_Discard(writer);
+    Py_END_CRITICAL_SECTION();
     return NULL;
 }
 

tests/isolated/multidict_repr_ft.py

@@ -0,0 +1,37 @@
+import os
+import subprocess
+import sys
+import sysconfig
+import textwrap
+
+FREETHREADED = bool(sysconfig.get_config_var("Py_GIL_DISABLED"))
+
+
+if __name__ == "__main__" and FREETHREADED:
+    child = textwrap.dedent("""
+        import signal, threading, time
+        signal.alarm(20)
+        from multidict import MultiDict
+        md = MultiDict([(f"k{i}", i) for i in range(50)])
+        errors = []
+        stop = threading.Event()
+        def repr_loop():
+            while not stop.is_set():
+                try: repr(md)
+                except Exception as e: errors.append(type(e).__name__)
+        def mutate_loop():
+            i = 0
+            while not stop.is_set(): md.add(f"m{i}", i); i += 1
+        ts = [threading.Thread(target=repr_loop, daemon=True) for _ in range(2)]
+        ts += [threading.Thread(target=mutate_loop, daemon=True) for _ in range(2)]
+        for t in ts: t.start()
+        time.sleep(0.3); stop.set(); time.sleep(0.05)
+        print(f"repr errors: {len(errors)}")
+    """)
+    subprocess.run(
+        [sys.executable, "-c", child],
+        env={**os.environ, "PYTHON_GIL": "0"},
+        capture_output=True,
+        timeout=60,
+        check=True,
+    )

tests/test_leaks.py

@@ -11,6 +11,7 @@
 @pytest.mark.parametrize(
     ("script"),
     (
+        "multidict_repr_ft.py",
         "multidict_extend_dict.py",
         "multidict_extend_multidict.py",
         "multidict_extend_tuple.py",