Using semaphores 2

[esserc]

I haven't been able to find any good examples of using semaphores to handle locking.

I have a script that can be used by multiple users at once. Certain procedures should only be run be one user at a time (seralized, more or less). What I would like to do is use semaphores to communicate between instances of the script and block operations if annother instance holds a lock.

I know I could do this with a lock file, but I think using semaphores would be a cleaner and faster method.

Does anyone have a good example of this?

BTW: I'm using Solaris, so I do support System V IPC.

 

[latch]

http://www.perldoc.com/perl5.6.1/lib/IPC/Semaphore.html

HTH

regards
C

"Brahmaiva satyam"
-Adi Shankara (788-820 AD)

 

[BobMCT]

My experience was that semaphore logic is/was not handled the same way in all platforms. What I did was use file 'flock'ing to a zero length file. I coded the cgi programs to flock the file. If the file was already locked the cgi would wait until it's turn came and it could lock it. Of couse you've got to remember to unflock it when done to make it available to the next in line.
Also, using an eval block you can set a timeout value so the flocks won't wait forever.


Works quite well.

 

[esserc]

Thanks for everyone's help. I ended using IPC::Semaphore. My script is only going to be run on Solaris, and I needed a FAST way of locking procedures, and this worked out a lot better than using files.