Fix race in test_start_new_thread_failed

When we succeed in starting a new thread, for example if setrlimit was ineffective, we must wait for the newly spawned thread to exit. Otherwise, we run the risk that the newly spawned thread will race with runtime finalization and access memory that has already been clobbered/freed. `_thread.start_new_thread()` only spawns daemon threads, which the runtime does not wait for at shutdown, and does not return a handle. Use `_thread.start_joinable_thread()` and join the resulting handle when the thread is started successfully.
python · mpage · Dec 3, 2024 · Dec 3, 2024 · Dec 3, 2024 · Dec 3, 2024
commit 7778368fd3eb6dca92a9a442141671f8218234c4
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
@@ -1192,11 +1192,12 @@ def f():
             resource.setrlimit(resource.RLIMIT_NPROC, (0, hard))
 
             try:
-                _thread.start_new_thread(f, ())
+                handle = _thread.start_joinable_thread(f)
             except RuntimeError:
                 print('ok')
             else:
                 print('!skip!')
+                handle.join()
         """
         _, out, err = assert_python_ok("-u", "-c", code)
         out = out.strip()