Signal Processing

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# 8  
Old 10-05-2001
Hello Perderabo,
I know that my method leaves a sleep process running if the timed command completes in time. I think that's harmless. It will be reaped by init when it exits. That's the only real cost of a very easily coded solution. Capturing and killing that last pid will drive script back up in complexity.

Does sleep process creates any kind of overhead for the unix system.

When I execute the following command (sleep 30; echo hello) &
, it create the two processes one is the shell process and the other is sleep process and the sleep process pid is always 1 greater than the shell process pid. Is it always true ?.
# 9  
Old 10-08-2001
Gee, thanks for the kind words guys!

No, you cannot just assume the next pid will be the current pid +1. You're on a multi-user machine. Stuff like cron runs all the time. If someone else forks first, they get the next pid. Also in a multi-cpu system, each cpu will usually reserve a chunk of 10 or so pids at once to cut down on spinlocks. Finally, pids recycle after pid 32,000.

The worst consequence of the sleep program in the background is that it is consuming a proc table entry. Too many of these and eventually you bump into maxuprc and cannot fork anymore. As long as that was not an issue, I'd just let it run. Remember that it will take code to remember or find the pid and then kill the pid. The load that this code would put on the system is trivial, but the only payback is the early death of a sleep can't make a profit.

If you really got to nail that last sleep process, a "kill $(ps -f | grep [s]leep |awk '{print $2}')" should get it.
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