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

Hi Perlmonks,

I need to execute parallel flows in my script.How do i obtain the following :

Start a process on linux.Without waiting for the process to complete, the script flow should go to the next step to determine the process id of the process initiated in the previous step.

I tried to run the process in the background . But that does not help my cause.Sample test script is mentioned below . This script still gives me sequential execution flow. 

#!/usr/software/bin/perl

my $sio_cmd = `./sio_linux random 100 1k 0 512k 20 1 testfile &`;

print "The command output = $sio_cmd";

$proc_cmd = `ps -ef | grep -i sio`;

print "\nThe process output is : $proc_cmd\n";

if($proc_cmd =~ /\w+?\s+?(\d+)\s+?.*$sio_cmd.*/){

        print "\nThe process id is : $1 \n";

}else{

        print "\nNo process id\n";

}

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After the execution of $sio_cmd ,the script should proceed to execute $proc_cmd without waiting for the process initiated by the execution of $sio_cmd to complete.

Thanks in advance.

Replies are listed 'Best First'.
Re: Parallel Execution Flows
by Corion (Patriarch) on Mar 08, 2010 at 08:59 UTC

    See open or fork, or perlipc for a general introduction, but that should have been covered in your course material already. Personally, I prefer open for IPC, because it's mostly like backticks except that it's asynchronous.

[reply]
      Thanks. When i replaced the backticks in the $sio_cmd with system, it worked for me.
[reply]

        You didn't read the documentation I linked to. Your approach will sporadically fail as soon as there is more than one process with the name sio in it, for example grep sio will also match that. Please read open, fork and/or perlipc.

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Re: Parallel Execution Flows
by cdarke (Prior) on Mar 08, 2010 at 15:39 UTC
    Like this?
    #!/usr/software/bin/perl

use warnings;
use strict;

my $sio_cmd = './sio_linux random 100 1k 0 512k 20 1 testfile';

# Create a new process
my $proc_cmd = fork();

if (!defined $proc_cmd) {
    die "Unable to fork: $!";
}
elsif ($proc_cmd == 0){
    # Child
    exec($sio_cmd);
    die "Unable to exec: $!";
}
else {
    # Parent
    print "\nThe process id is : $proc_cmd \n";
    # Do some stuff

    # Could use waitpid() instead
    wait();
    print "Child exited with: ",$? >> 8,"\n";
}

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