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Process to process synchronization (unix)

Michael Stenner mstenner at phy.duke.edu
Tue Mar 19 14:01:19 EST 2002 
On Mon, Mar 18, 2002 at 11:16:55AM +0000, Eric Brunel wrote:
> Gillou wrote:
> > I have a Zope application and another running process (in python too).
> > I need to transmit data and signal (hey ! data available, do your job !)
> > in an asynchronous way from the Zope app (in an external method) to the
> > python running process (that runs for another user).
> > The other process waits for the signal, takes given data, does the jobs
> > and waits further signal (...)
> > I'm 99.9% newbie in process to process communication.
> > What packages are helpful for this ?
> 
> The two means that come to my mind are:
> - named pipes: quite easy to handle, as they are manipulated just like 
> files. The problems are that named pipes are quite difficult to synchronize 
> if both processes should send data to the other, and that's it's a 
> Unix-only solution. All functions manipulating named pipes are built-ins or 
> in module os. If you choose that, I may also provide a few simple examples.
> - sockets: a bit trickier to handle, but far more practical for two-way 
> communications and multi-platform. The Python module to handle them is 
> simply socket. There's an example in the library reference (see 
> http://www.python.org/doc/current/lib/socket-example.html).

It's always seemed to me that named pipes have limited usefulness.
They seem like a bit of a hack that have two major selling points.

1) they are truly persistent in the sense that neither program has to
   "set them up" (although _someone_ does... just not for each
   instance of the program) and they continue to exist when both
   programs are gone.

2) it is REALLY easy to take a program that writes (or reads, but
   writes is easier) to a file, and make it write to a named pipe.

The latter is the more persuasive.  If you have someone else's program
that writes to a file only, but you want to do something more "active"
with the output, you can make the file a named pipe.

Anyway, other than that, I don't see much going for named pipes.
Sockets are nice because they don't require that you have extra crap
in the filesystem, and they can easily be made network-aware.  (Have
the two processes run on two different machines).

Bottom line... I would use sockets.
					-Michael
-- 
  Michael Stenner                       Office Phone: 919-660-2513
  Duke University, Dept. of Physics       mstenner at phy.duke.edu
  Box 90305, Durham N.C. 27708-0305
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