Thread unsafety with 3.13t: "ValueError: tool 1 is not in use"

[nedbat]

This happens occasionally when running the full test suite on my Mac:

tests/test_concurrency.py::test_thread_safe_save_data
  /Users/ned/coverage/trunk/.tox/py313t/lib/python3.13t/site-packages/_pytest/threadexception.py:82: PytestUnhandledThreadExceptionWarning: Exception in thread Thread-10 (random_load)

  Traceback (most recent call last):
    File "/usr/local/pyenv/pyenv/versions/3.13.3t/lib/python3.13t/threading.py", line 1041, in _bootstrap_inner
      self.run()
      ~~~~~~~~^^
    File "/usr/local/pyenv/pyenv/versions/3.13.3t/lib/python3.13t/threading.py", line 992, in run
      self._target(*self._args, **self._kwargs)
      ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/Users/ned/coverage/trunk/tests/test_concurrency.py", line 673, in random_load
      mod = import_local_file(module_name)
    File "/Users/ned/coverage/trunk/coverage/misc.py", line 300, in import_local_file
      spec.loader.exec_module(mod)
      ~~~~~~~~~~~~~~~~~~~~~~~^^^^^
    File "<frozen importlib._bootstrap_external>", line 1026, in exec_module
    File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
    File "/private/var/folders/6j/khn0mcrj35d1k3yylpl8zl080000gn/T/pytest-of-ned/pytest-14/popen-gw1/test_thread_safe_save_data0/test_modules/m192.py", line 0, in <module>


      def f(): pass

    File "/Users/ned/coverage/trunk/coverage/sysmon.py", line 369, in sysmon_py_start
      sys_monitoring.set_local_events(self.myid, code, local_events)
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  ValueError: tool 1 is not in use

    warnings.warn(pytest.PytestUnhandledThreadExceptionWarning(msg))

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

[nedbat]

Fixed in commit 8b9cecc.

[nedbat]

This is now released as part of coverage 7.8.1.