Re: Keeping track of children from previous runs of a script

Several options:

Make the children create files containing their PID in some directory when they start and remove them when they exit. The problem with this approach is that children may exit without cleaning up its pid file and another unrelated process may take the same PID before you restart the main one (though most OSs try to avoid reusing pids as much as possible)
Capture signals on the parent and make it kill the children before exiting. The problem here is that not all signals can be trapped.
Monitor the PID of the parent process (getppid) on the children and abort when it becomes 1.
Comment on Re: Keeping track of children from previous runs of a script

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Re^2: Keeping track of children from previous runs of a script by Illuminatus (Curate) on Mar 10, 2011 at 17:40 UTC
I think salva's first option is the best way to go. If you are really paranoid about PID-wrap, you could put the executable name in the file along with the PID. Then, if you determine that the PID is active, you can use a variety of methods to determine the executable name and match that as well. fnord	[reply]
Re^3: Keeping track of children from previous runs of a script by salva (Canon) on Mar 10, 2011 at 18:00 UTC
ajwood, note also that the methods described in my post are not mutually exclusive. Actually, it is quite common to combine the first two.	[reply]
Re^2: Keeping track of children from previous runs of a script by JavaFan (Canon) on Mar 10, 2011 at 18:33 UTC
To avoid the problem of processes exiting before cleaning up, one could do the following: after the child has created its PID file, the child should lock the PID file. The lock will be gone as soon as the process exits - no matter what the reason of exiting is (well, I'm assuming a UNIX OS, I've no idea how other OSses work). To check whether a previous child is still running, open the PID files, and try to get a lock. If you can get a lock, the process is no longer running. Only if the file exists, and it's still locked, the process is still running. It also solves the problem of PID reuse.	[reply]