foreach my $host (@arrayofhosts) {
  defined (my $pid = fork) or die "Cannot fork: $!";
  unless ($pid) {
    # go to town with $host
    exit 0; # very important!!! don't let it get past here
  }
}
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-- Randal L. Schwartz, Perl hacker

because that would fork-bomb a machine if the array is large.

i did this in a previous script:

my $fork_num = ( $#hostlist <= MAXFORK ? $#hostlist : MAXFORK );

for ( 0..$fork_num ) {

    ##
    ## create bi-directional socket for parent/child communication

    my $to_child = IO::Socket->new();
    my $to_parent = IO::Socket->new();

    socketpair($to_child, $to_parent, PF_UNIX, SOCK_STREAM, PF_UNSPEC)
        or die "Couldn't create socket pair:  $!\n";

    my $pid;
    if ( $pid = fork ) {
                
        ### parent process

        undef $to_parent;
        $to_child->autoflush;

        $children{$pid} = $to_child;

        sleep 1;
        next;

        }

    else {

        ### child process

        undef $to_child; undef %children;
        $to_parent->autoflush(1);

        local $SIG{PIPE} = sub { print " CAUGHT PIPE\n\n";
                                                die "Signal caught in 
+Child $$:  $!\n"; };

        ## 
        ## main processing occurs in the subroutine.  

        &process_config_job($fork_num, $to_parent);

    }

}
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the child processes have a sub getnexthost() which asks the parent for another hostname.

the parent process has a subroutine to read the request for a new hostname then send it.

i don't like the 'fork foreach' idiom. good way to crash a box.

I was literally implementing what the original poster had needed. For a better solution, I would refer once again (twice in as many days) to my column on making a pre-forking hungry puppies implementation.

-- Randal L. Schwartz, Perl hacker

while (host = pop array_of_hosts) {
   fork   
   if child {
      work on host
      exit
   }
}
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Thanks a lot from a wannabe monk with 0 reputation :)

Hi,

My idea is that the parent pop's the stack right after the fork, so that the value the child process got is no longer in the stack. Is this the right thing to do, or is there a "right thing to do"?

I'm not all that familiar with fork() (I spend most my time on Win32). But wasn't Fastolfe's suggestion basically what you asked for? except more efficient.

The while (host = pop array_of_hosts)does the pop before the child is created, all the child needs to know is the value of $host, it doesn't need to pop, because the parent has already taken care of it.

Update: I've just read up a bit on fork. If I were you, I would develop Merlyn's snippet. It's a little less pseudocode than Fastolfe's but basically the same. You could add a sleep() in there for the parent so you don't spawn too many children and overload the CPU which concerned geektron.

To just explain Merlyn's a bit further (and alter it a bit to utilise pop):

while (my $host = pop @arrayofhosts) {    # $host is no longer in the 
+array
  defined (my $pid = fork) or die "Cannot fork: $!";  # self-explanato
+ry
  unless ($pid) {         
    # only the child will execute this code from here ...
         # do some things with $host
    exit 0; # very important!!! don't let it get past here
    # to here. At this point, the child process will terminate ...
  }

    # The parent continues here after forking the child
    # here it can do what it wants. 
    # you can rest here a while so you don't have too many zombies

    sleep (10);
    # now do some more things before forking the next child process

}
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