hanging when I use --time-methid=signal

i am making a unittest,
`for index, test_case in enumerate(test_cases[start_case_index:], start=start_case_index):
test_case_name = test_case.split("::")[-1]
print(f"Running {test_case_name}")

    pytest.main(['-v', '--tb=short', '--capture=no', '--timeout=20', '--timeout-method=signal', test_case], plugins=[recorder])
    
    result_data = recorder.results.get(test_case)
    if result_data is None:
        result_data = {
            "outcome": "not executed",
            "duration": 0,
            "timestamp": datetime.now().isoformat()
        }`

above is my test code, if one case is out of time, the process will hang and show log like below and would not break out to next test case,what shoukd I do?
++++++++++++++++++++++++++++++++++++++++++++++ Timeout ++++++++++++++++++++++++++++++++++++++++++++++

  File "/usr/lib/python3.10/threading.py", line 973, in _bootstrap
    self._bootstrap_inner()
  File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.10/threading.py", line 953, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib/python3.10/concurrent/futures/thread.py", line 83, in _worker
    work_item.run()
  File "/usr/lib/python3.10/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/workspace/bailuan/20240105_iree_chiptech/iree/tests/e2e/dlc_specific/test_runner.py", line 461, in thread_task
    result = run_test(fn, inputs, output_num, global_config_path,
  File "/workspace/bailuan/20240105_iree_chiptech/iree/tests/e2e/dlc_specific/test_runner.py", line 428, in run_test
    output_fns1 = run_in_backend("dlc")
  File "/workspace/bailuan/20240105_iree_chiptech/iree/tests/e2e/dlc_specific/test_runner.py", line 406, in run_in_backend
    run_result = subprocess.run(
  File "/usr/lib/python3.10/subprocess.py", line 505, in run
    stdout, stderr = process.communicate(input, timeout=timeout)
  File "/usr/lib/python3.10/subprocess.py", line 1154, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
  File "/usr/lib/python3.10/subprocess.py", line 2021, in _communicate
    ready = selector.select(timeout)
  File "/usr/lib/python3.10/selectors.py", line 416, in select
    fd_event_list = self._selector.poll(timeout)
++++++++++++++++++++++++++++++++++++++++++++++ Timeout ++++++++++++++++++++++++++++++++++++++++++++++

Reproduce the hang with the shown pytest.main loop and --timeout-method=signal, then inspect the timeout output from iree/tests/e2e/dlc_specific/test_runner.py, especially thread_task, run_test, run_in_backend, and subprocess.run. Trace how the timed-out worker and subprocess are handled; done means a timed-out case returns control to the loop and the next test case runs without leaving the process hanging.