class mutex

[Olivier Dagenais]

I looked into this when I had to synchronize CGI processes.  The best idea I
have found is to try to open a file in write mode when someone else has
already opened it in write mode and has made it read-only.  It didn't work
with the built-in open function, but it did when I tried the low-level
sys.open (I think that's the one, maybe it was os.open??)..

I've attached vaisselle.py (it means "dishes" in french), which contains the
class "Chopstick" - which does the actual locking and blocking - (I got the
idea for the name after the "dining philosophers problem") and the secret
class "Napkin" which attempts to maintain a queue of the requests made to
the lock.

The "proc.py" example program creates a 3-meg file, after making sure it has
acquired the "cs1" lock.  Start a few instances of it in different windows
and see what happens!

It's not very elegant, but it worked on my Win95 machine.  I wanted to test
it on a Unix machine, but I didn't get around to it.  I make no guarantees
about that code, it was purely experimental and I'm not so such some of the
operations are "atomic enough" to be a good semaphore.

Good luck, I've now switched to using threads to avoid this mess.  I may get
back to it later, in the future...

--
----------------------------------------------------------------------
Olivier A. Dagenais - Software Architect and Developer
"Someone called 'Type your name here' is impersonating me on the
internet and is posting exactly the same things I am posting!"


"Prof. Peter Stoehr" <peter.stoehr at weihenstephan.org> wrote in message
news:39F1E7B8.D2E0F2AB at weihenstephan.org...
> Hi out there,
>
> there is a class mutex shipped with python. I've tried to use it to
> syncronise two processes created with os.fork() and failed :-(
> Looking at the source code of mutex.py I found out, that it is
> implemented in pure python. Thus, it does not implement a real
> mutex-object as a python code can be interrupted after each step of the
> byte-code.
> Based on that, I have two questions:
> 1) Does python provide a real mutex object.
> 2) What is the use of the class mutex
>
>     Greeting
>         Peter
> --
> --------------------------------------------------------------------------
-
>   Prof. Peter Stoehr --- Teisenbergweg 6 --- 85435 Erding ---
> 08122/47232
>       http://www.weihenstephan.org/home/ak/support/team/jpg/peter.jpg
> --------------------------------------------------------------------------
-
> I'm the terror that flaps through the night


begin 666 proc.py
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`
end

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`
end