call site 2 for _thread.WorkerPool.shutdown
thread/testing/test_pool.py - line 65
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   def test_maxthreads():
       pool = WorkerPool(maxthreads=1)
       def f():
           py.std.time.sleep(0.5)
       try:
           pool.dispatch(f)
           py.test.raises(IOError, pool.dispatch, f)
       finally:
->         pool.shutdown()