fork child process

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

I need to fork child process for each array element. I'm using below code :

 
#!/usr/bin/env perl
my $pid;
my @a = (1,2,3);
for my $i (@a) {
    print "i -> $i \n";
    $pid = fork();

    if ( $pid ) {
        # parent
        print " child pid : $pid \n";
    } elsif ( $pid == 0) {
        #child
        #print "child working on $i ";
    }
}
    
while((wait()) > 0) {};

exit
[download]

but executing the code results in child processes more than the no. of elements in array. I don't know what's the problem. Output look like : i -> 1 child pid : 12629 i -> 2 i -> 2 child pid : 12631 i -> 3 child pid : 12630 i -> 3 child pid : 12632 i -> 3 child pid : 12633 i -> 3 child pid : 12634 child pid : 12635

Comment on fork child process Download Code

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Re: fork child process by Corion (Patriarch) on Apr 14, 2015 at 08:23 UTC
Your forked children continue the loop. Most likely, you don't want to do that. Either use `exit` when your child completed its work or use a wrapper like Parallel::ForkManager, which provides idioms that make working with forked children easier.	[reply] [d/l]
Re: fork child process by hippo (Archbishop) on Apr 14, 2015 at 08:22 UTC
Both the children and the parents are inside the loop.	[reply]
Re: fork child process by jeffa (Bishop) on Apr 14, 2015 at 16:44 UTC
As others have already pointed out, you need to explicitly call `exit` in the portion that will be executed by the child processes. In other words, try something a bit more like this: `#!/usr/bin/env perl use strict; use warnings; my @a = (1,2,3); for my $i (@a) { my $pid = fork(); if ( $pid == 0 ) { print "$i -> i am a forked child\n"; exit; } else { print "$i -> forking $pid\n"; } } while((wait()) > 0) {};` [download] See perlfork and perlipc for more examples. jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply] [d/l] [select]