Re: delay loop

[zentara]

I didn't write this, but it does seem to answer your needs. Another option is to actually use an eventloop system like Glib or AnyEvent.

#!/usr/bin/perl 
use warnings;
use strict;

# by some monk here at perlmonks

# wait basically waits until one of the children exits. 
# It is used to avoid having Zombie processes: if you don't 
# wait() for them, and you go a long time in your parent 
# process before exiting, you'll see these processes in 
# the process list even if they already exited, marked as 
# "zombie" (this means that resources in the kernel associated 
# to the process aren't freed). So, wait is the way by which 
# the parent process acknowledges the kernel of the son's death. 
# It's interesting that this mechanism actually tries to force 
# the programmer not to ignore return values from child processes, 
# much like the good practice of never throwing away return values 
# from functions.
# Moreover, wait returns as soon as the first child exits; in 
# the OP's post, (s)he created 8 of them, and had to wait until 
# all of them have exited. According to perldoc -f wait, a call 
# to the wait function returns -1 if, and only if, there are no 
# more children alive(1) - thus the cycle.
#  If you happened to set $SIG{'CHLD'} to 'IGNORE', 
# this zombie-ridding happens automatically, and you're likely to 
# have wait always return -1 - but I guess it's not the case with 
# this thread :) Moreover, in this case I would discourage the 
# OP to do that, because (s)he's using wait as a synchronisation 
# mechanism to understand when all the children exited. BTW, this 
# is documented in perldoc perlipc, but I suggest taking a look in 
# perldoc perlport as well. 


for ( my $i = 0 ; $i < 11 ; $i++ ) {
    defined( my $pid = fork() ) or print STDERR "Unable to fork!";

    if ($pid) {
        print "Child $i is $pid\n";
    }
    else {
        print "Hi!  I'm just a kid.. I'm going to sleep now..\n";
        sleep rand(10);
        print "*Yawn* I'm awake!  Huh?  It's me! Kid $$!  Bye bye!  
                                              $$ Time to die!\n";
        exit 0;
    }
}

#this is correct
   1 while wait > 0;
# wait by itself is different
#  wait;


print "Screw this, I'm done waiting for those kids\n";