how can we tell when a background process is finished?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: how can we tell when a background process is finished? by dave_the_m (Monsignor) on Jun 20, 2004 at 09:51 UTC
If we run system("program &");, is there a way to know when "program" has finished its execution? No. Instead, create a signal handler for SIGCHLD, then fork(), and do `system("program")` in the child. Dave.	[reply] [d/l]
Re^2: how can we tell when a background process is finished? by integral (Hermit) on Jun 20, 2004 at 10:39 UTC
Or you can do `exec("program")` in the child, saving another process, since system() incorporates a fork+exec. -- integral, resident of freenode's #perl	[reply] [d/l]
Re^2: how can we tell when a background process is finished? by Anonymous Monk on Jun 20, 2004 at 11:34 UTC
Thanks...do you know where I can find an example of this? I understand how to fork and then do `system("program")` in the child, but I'm not sure how to handle the "signal handler" for SIGCHLD. I think I will have to use waitpid()?	[reply] [d/l]
Re^3: how can we tell when a background process is finished? by DaWolf (Curate) on Jun 20, 2004 at 14:29 UTC
Take a look at perlmonkey's MP3 server with IO::Socket tutorial. It explains in the fifth paragraph exactly what you're asking about processes. Best regards, my ($author_nickname, $author_email) = ("DaWolf","erabbott\@terra.com.br") if ($author_name eq "Er Galvão Abbott");	[reply]
Re: how can we tell when a background process is finished? by dfaure (Chaplain) on Jun 20, 2004 at 10:43 UTC
You may use the trick running my $pid = (`program &;echo $!`)[0]; [download] which gives you the id of background process. Then you may wait for this process to end. Not a very clever solution but you may have a try. [approx. syntax, please check...] -- HTH, Dominique If the only tool you have is a hammer, you will see every problem as a nail. -- Abraham Maslow	[reply] [d/l]
Re: how can we tell when a background process is finished? by vek (Prior) on Jun 20, 2004 at 20:00 UTC
Perhaps you could explain what you are trying to do. For example, if you just need to wait for a program to finish, why place it in the background to begin with? A simple `system("program");` would suffice. That way you always know when the program has finished because `system` will return. -- vek --	[reply] [d/l] [select]