dude01 has asked for the wisdom of the Perl Monks concerning the following question:

I want to call a subroutine in the background from within another subroutine in my perl program. How do I do that. I have 
sub getProc { #do some stuff }

sub getInput {
    while(<FILE>) {
        # do some stuff
        # call getProc but run it in the background
    }

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Replies are listed 'Best First'.
fork
by howard40 (Beadle) on Mar 01, 2001 at 10:19 UTC
    Here's an extremely simplistic example of how to fork a child process off and have it running alongside the parent... if you want to do something simple and non-vital, you could do it this way...

    beware though, there are many problems and pitfalls with forks. (perhaps in a future version of perl, there'll be a spork() function that will eliminate some of the problems with fork() :))

    To use this code, just replace the while() loops with whatever function calls you need to make... hope it helps 
    #!/usr/bin/perl
use strict;
my $k_pid;


die "Can't fork! ($!)" unless defined ($k_pid = fork());

my $i = 1;
my $n = 1;


  if ($k_pid) {
    #parent code
    while (1==1) {
        $n++;
        print "Parent ($i)($n) \n";
        sleep(1);
    }
    kill("TERM" => $k_pid);
    
  } else {
    #child code
    while (1==1) {
        $i++;
        print "Child: ($i)($n)\n";
        sleep(1);
    }

  }

    [download]
[reply]
[d/l]
Re: How do run a subroutine in the background
by AgentM (Curate) on Mar 01, 2001 at 07:40 UTC
    You can find an explanation of the weakness inherent in PerlThreads AND a potential solution here. Keep in mind that on Winduz, fork is not supported well (minimal functionality).
    AgentM Systems nor Nasca Enterprises nor Bone::Easy nor Macperl is responsible for the comments made by AgentM. Remember, you can build any logical system with NOR.
[reply]
Re: How do run a subroutine in the background
by rpc (Monk) on Mar 01, 2001 at 07:13 UTC
    One option is to use Thread, but this (probably) requires recompiling perl. Without threads, you can't run a single subroutine in the background; it has to be an entire process. For this, use fork.
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[d/l]
Re: How do run a subroutine in the background
by enoch (Chaplain) on Mar 01, 2001 at 10:23 UTC
    Here is the basic code for forking another process. Have fun. 
    sub getProc { #do some stuff }

sub getInput {
    while(<FILE>) {
        # do some stuff up here...
        $childPid = fork(); #fork a process
    
        if($childPid == 0)
        {
            #okay, in the child
            #call getProc
            getProc();
        }
        else
        {
            # okay, we are in the parent,
            # so, let's continuing doing what we do
        } } }

    [download]

    Jeremy
[reply]
[d/l]
Re: How do run a subroutine in the background
by tomhukins (Curate) on Mar 01, 2001 at 15:35 UTC
    If you don't want to get to grips with threads or IPC, POE can be a simple way of doing this.
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Re: How do run a subroutine in the background
by Beatnik (Parson) on Mar 01, 2001 at 13:40 UTC
    If you're gonna use Threads (limits, requirements, pitfalls, etc mentioned above) , you might as well look at perlthrtut

    Greetz
    Beatnik
    ... Quidquid perl dictum sit, altum viditur.
[reply]
perldoc ipc stuff
by howard40 (Beadle) on Mar 01, 2001 at 10:05 UTC
[reply]

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