Attached is a test Python script that you can run to see the race condition in action. There are two Python scripts: pipe.py and reader.py.

 - pipe.py: make two subprocess.Popen() calls from two different threads.

 - reader.py: (its content is in the bottom comments of pipe.py, so move it to a separate file): reads lines from stdin and exits

Basically, pipe.py creates a pipe between "echo Hello World!" and "python reader.py".

You'll see that pipe.py will hang until ctrl+c is entered, even though the first subprocess in the pipe, reader.py, exits. Uncommenting the time.sleep() call will cause the first subprocess.Popen() time to properly close the inheritable handles before the second subprocess.Popen() call is made in the other thread, thus the inheritable handles are leaked.