[Mailman-Developers] Re: Extraordinary locking mechanisms...

Jeremy Hylton jeremy@cnri.reston.va.us
Wed, 10 May 2000 12:36:04 -0400 (EDT)

[Dan A. Dickey wrote:]
>Well, I figure its finally time for me to aska stupid question.
>Why do people use filesystems for locking?
>Why not use IPC semaphores instead?
>It seems that people are going through extraordinary
>trouble and grief to get the filesystem locking correct.
>Like I said - it may be a stupid question, and I'm
>just not getting something.  What is that something?

Chris pointed at that mailman runs as a distributed system, so IPC
won't work.  The idea, though, of using something other than the
filesystem for locking makes good sense.  The locking could be based
on a server that communication with other mailman components over a
socket.  It would look basically like the Javaspaces leasing service.
(Leases are basically locks that timeout.)  The only worry I would
have is about crashes of the lease service.  For a single machine, it
could run under init; for multiple machines, a leader election
protocol would be necessary to guard against machine crashes.