On Saturday 27 November 2004 22:46, fredex wrote: > What I've done in C programs is to create the lock file and put my > PID in it. Whenever the program starts, if the lock file is not present > it's safe to start (assumed). If it's present, open it and read the PID > value. Look up the PID to see if it still exists. If it does, assume it > is the correct process (which it may not since PIDs do get recycled in > time) and abort the program. If the file exists and the PID doesn't, > the program probably died without cleaning up, so just delete the lock > file then create a new one with your own PID. During the process of > creating the file, you need to lock it to avoid race conditions. In > C I'd use fcntl or lockf or some such. I don't know what you'd do in > PERL but there surely is a mechanism. That's quite a tricky (though widely practiced) scheme to paper over Unix's traditional lack of proper locking semantics. I've never understood why it was omitted; perhaps the original designers didn't understand the need. I was using OS Rel 20 or so about then, and it did have a straight-forward mechanism. Now we have proper locking, I think we should use it. Even though it's not as good as I had bask then. -- Cheers John
