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Date: Fri, 18 Oct 2013 20:08:31 -0600
Subject: Re: Inter-process locking
From: Jason Friedman <jsf80238@gmail.com>
To: Piet van Oostrum <piet@vanoostrum.org>
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Xref: csiph.com comp.lang.python:57085

> There is one caveat, however. If a process that has the lock crashes with=
out releasing the lock, the lock file will stay around and prevent other pr=
ocesses to acquire it. Then you will have to manually remove it. I generall=
y prefer a solution where the pid of the locking process is written to the =
lock file, so that other processes trying to acquire the lock can find out =
if the process is still around and remove the lock file if not. I have seen=
 such solutions on Unix systems. But I am not sure if this can be done in a=
 platform independent way without the risk of race conditions. Maybe I have=
 to find out.

True, luckily my application need not be that accurate.  Competition
for the lock will be rare.  My present solution waits a few minutes
for the lock to become available, and if not available after that time
takes it forcefully (which lockfile handily provides).  Certainly not
foolproof, but we can recover merely by re-running, so if I get an
error or two each year that is acceptable.