wait/waitpid returns -1 when there are no children or the children are automatically being reaped ( according to perldoc -f wait ). So the loop is waiting for all of the children to exit
I personally don't like this child count decrementing business... I'd rather explicitly check if the pid that I just got is the pid that I'm waiting for, i.e., my child. That may just be me...
## XXX - I use hashes in this type of situation
## because I usually associate more meta data to a pid
## which must be used by the parent when the child
## exits... and delete $hash{ $foo } is cleaner
## than splice() to me :)
use POSIX;
my %pids;
for( 1 .. $numchild ) {
my $pid = fork();
## check if $pid id defined, etc.
if( $pid ) { ## parent
$pids{ $pid } = 1;
} else {
do_interesting_stuff();
exit;
}
}
while( ( my $pid = waitpid(-1, POSIX::WNOHANG() ) ) > 0 ){
if( exists $pids{ $pid } ) {
delete $pids{ $pid };
} else {
print STDERR "Unknown child $pid\n";
}
}