requested changes

Author: tom-pytel

Lib/test/test_hashlib.py

@@ -1196,8 +1196,13 @@ def test_file_digest(self):
             with open(os_helper.TESTFN, "wb") as f:
                 hashlib.file_digest(f, "sha256")
 
-    @unittest.skipUnless(support.check_sanitizer(thread=True), "only meaningful on free-threading")
-    def test_gh_128657(self):
+    # There was a data race in py_digest_by_name() which caused tsan to
+    # complain and might sometimes cause an extra refcount in `PY_EVP_MD`
+    # structure if two threads attempted to create a `sha256()` at the same
+    # time. See gh-128657.
+    @unittest.skipUnless(support.Py_GIL_DISABLED,
+                         "only meaningful on free-threading")
+    def test_py_digest_by_name_data_race(self):
         def test_hashlib_sha256():
             hash_obj = hashlib.sha256()
 
@@ -1206,18 +1211,17 @@ def closure(barrier):
             test_hashlib_sha256()
 
         num_workers = 40
-        num_runs = 20
+        barrier = threading.Barrier(num_workers)
 
-        for i in range(num_runs):
-            barrier = threading.Barrier(num_workers)
-            thrds = []
+        with threading_helper.catch_threading_exception() as cm:
+            threads = [threading.Thread(target=closure, args=(barrier,))
+                       for _ in range(num_workers)]
 
-            for i in range(num_workers):
-                thrds.append(thrd := threading.Thread(target=closure, args=(barrier,)))
-                thrd.start()
+            with threading_helper.start_threads(threads):
+                pass
 
-            for thrd in thrds:
-                thrd.join()
+            if cm.exc_value:
+                raise cm.exc_value
 
 
 if __name__ == "__main__":