JeffR100 has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to run multiple proccesses at the same timeand I do not care about the order in which they run or whether they wait for eachother. Basically, I am trying to replicate what I would get from typing: "MyProgram &" multiple times at the command line. There is probably some very simple solution to this problem that I am forgetting about, but either way, I can;t figure out how to do it. I have tried using backticks, but the program waits for the process within the ticks to end before continuing on and launching teh next process. I think that I might be able to use exec and fork, but I am not sure exactly how I would use them to accomplish my task. Thanks, Jeff

Replies are listed 'Best First'.
Re: Launching multiple processes
by Paladin (Vicar) on Jan 06, 2004 at 22:54 UTC
    Take a look at Parallel::ForkManager. It takes care of all the forking and execing for you, and gives you good control over the child processes.
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Re: Launching multiple processes
by dominix (Deacon) on Jan 06, 2004 at 23:48 UTC
    check this column from merlyn it's a good starting point, there is a clear explanation of process launching and control.
    --
    dominix
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Re: Launching multiple processes
by Roger (Parson) on Jan 06, 2004 at 23:06 UTC
    Quick solution using fork and exec.
    my $program = '/bin/ls';
my $num_children = 5;

$SIG{CHLD} = 'IGNORE';

for (1..$num_children) {
   defined ( my $pid = fork ) or die "Can not fork!";
   if (!$pid) {
      # in child process
      exec $program;
   }
}

    [download]
    Update: fixed the logical bug with fork, if fork returns pid of 0 (parent) the code would die too. undef and 0 both evaluates to false. Thanks to borisz to point out below. Zaxo is right too. ;-)

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[d/l]
      the fork line should be written as 
        defined ( my $pid = fork ) or die "Can not fork!";

      [download]
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[d/l]

      Another bug: You have the makings of a fine fork bomb. If I calculate right, you'll get 20 instances of /bin/ls from that. Call the child program with exec or else exit after system.

      Don't forget to zombie-proof it with wait or $SIG{CHLD), either.

      After Compline,
      Zaxo

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Re: Launching multiple processes
by dpuu (Chaplain) on Jan 06, 2004 at 23:47 UTC
    The simplest way is probably to do precisely the thing that you want to emulate: 
      system "MyProgram &";

    [download]
    --Dave
    Opinions my own; statements of fact may be in error.
[reply]
[d/l]
      Thanks for the simple idea. I assumed that since a & between backticks didn't work, it wouldn't work with system() either. Jeff
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