add atomic global counter system

multidict/_multilib/state.h

@@ -5,6 +5,8 @@
 extern "C" {
 #endif
 
+#include <stdatomic.h>
+
 /* State of the _multidict module */
 typedef struct {
     PyTypeObject *IStrType;
@@ -128,7 +130,7 @@ get_mod_state_by_def(PyObject *self)
 static inline uint64_t
 NEXT_VERSION(mod_state *state)
 {
-    return ++state->global_version;
+    return atomic_fetch_add_explicit((_Atomic(uint64_t)*)&state->global_version, 1, memory_order_relaxed);
 }
 
 #ifdef __cplusplus

tests/isolated/multidict_global_counter.py

@@ -0,0 +1,33 @@
+import threading
+import multidict
+from multidict import MultiDict
+import sysconfig
+
+FREETHREADED = bool(sysconfig.get_config_var("Py_GIL_DISABLED"))
+if not FREETHREADED:
+    raise SystemExit(0)
+
+md = MultiDict()
+N, M = 3, 100
+baseline = multidict.getversion(md)
+
+
+def worker(tid):
+    for i in range(M):
+        md[f"k{tid}_{i}"] = i
+
+
+if __name__ == "__main__":
+    threads = [threading.Thread(target=worker, args=(tid,)) for tid in range(N)]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+    observed = multidict.getversion(md) - baseline
+    expected = N * M
+    assert expected == observed, (
+        f"expected delta: {expected}"
+        f"   observed: {observed}   "
+        f"lost: {expected - observed}"
+    )

tests/test_leaks.py

@@ -18,6 +18,7 @@
         "multidict_type_leak.py",
         "multidict_type_leak_items_values.py",
         "multidict_pop.py",
+        "multidict_global_counter.py",
     ),
 )
 @pytest.mark.leaks