Comment 9 for bug 1327946

Getting closer I think, the algorithm could be,

Try to run the following:

posix_ipc.Semaphore("xyz002",flags=posix_ipc.O_CREAT,initial_value=os.getpid())

If this fails, read pid from existing Semaphore?, check if that pid exists, if not, then atomically unlink it and try the later statement again? That atomic part is what I am wondering about, how do we atomically unlink it and run the above statement at the same time?

For example:

Process1,

* Try above statement, fail
* Read semaphore pid and find process dead/gone that owned it.
* Sleep for 3 seconds (or > 3...)
* Unlink *wrong* semaphore, try the above statement again, succeed.

Process2,

* Try above statement, fail
* Read semaphore pid and find process dead/gone that owned it.
* Unlink *right* semaphore, try the above statement again, succeed.