5. You now own the file. When you're done, unlink the file.

Please also delete the file when you crash or are killed, e.g. by SIGKILL.

Yes, I know that's not possible. That's part of why PID files suck, and that's what a monitoring process like supervise from djb's daemontools or even the stinking systemd fixes. And due to the way Unix systems work, all that the monitoring process needs to do is to wait for SIGCHLD or a new task, e.g. sending a signal to the monitored process. In other words: The monitoring process usually does nothing, it is not in the run queue and perhaps swapped out, so it can't do anything wrong. ;-) The O/S kernel will run the monitoring process when anything needs to be done. This reduces the monitoring process to a few lines of code. supervise.c is less than 300 lines, including full error checking.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

In reply to Re^5: Mechanism for ensuring only one instance of a Perl script can only run? by afoken
in thread Mechanism for ensuring only one instance of a Perl script can only run? by redapplesonly

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