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gokuraku has asked for the wisdom of the Perl Monks concerning the following question:
I'm kind of looking for some brainstorming here, my problem is this. I have a perl script that runs some various commands as part of a test harness, one of them gets hung but only when the perl script is run as a background process. I would like to set my script so that if its running as a background process then skip that test, otherwise run it, but I am unsure what is the best way to tell if the script is being run in the background.
In looking at Proc::Background I thought it might be able to do it by that, but I didn't see an obvious way to check if the process itself was being run in the background. It seemed plausible that I might be able to check and see if the process had a parent, but when I run a process in the background its not really forked, at least from what I can tell.
Has anyone tried something similar to this before? I'd like to get some ideas and see what I can figure out, its a good mental exercise.
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Re: Is Process Running In The Background?
by Joost (Canon) on Apr 28, 2008 at 13:21 UTC
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It seemed plausible that I might be able to check and see if the process had a parent, but when I run a process in the background its not really forked, at least from what I can tell.
Assuming UNIX/POSIX behaviour:
- all processes except init have a parent process id (though the parent process may have already exit()ed).
- conceptually at least, the only way to start a new process is to fork() an existing one. Which explains 1.
- you can test if your program is running interactively by seeing if STDIN and STDOUT are connected to terminals (see -t). Note that plain backgrounded programs can still be interactive, while fully daemonized programs aren't.
- IOW, running
interactively non-interactively isn't the same as running in the background. See also POSIX's tcgetpgrp() and tcsetpgrp().
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Re: Is Process Running In The Background?
by hipowls (Curate) on Apr 28, 2008 at 12:12 UTC
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Re: Is Process Running In The Background?
by haoess (Curate) on Apr 28, 2008 at 12:17 UTC
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Re: Is Process Running In The Background?
by rowdog (Curate) on Apr 28, 2008 at 19:14 UTC
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[d/l] |
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Very nice...thank you it is what I needed.
This is running on HPUX and the one I found that works is the following:
$tpgrp = tcgetpgrp(fileno(*TTY));
$pgrp = getpgrp();
if ($tpgrp == $pgrp) {
system("which which > whichtest");
} else {
print "Skipping which as we are not interactive.\n";
}
I needed a change in this as the system call on HPUX gets the shell into a waiting state until it receives some input, which does not work well if we run it as a background process. Rather than skip doing this as a check, which we could do as the script is run manually at times, I wanted a way to have it run only when we needed it.
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[d/l] |
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