If your not stuck on using processes, it's pretty simple with threads.

#! perl -slw
use strict;
use threads;
use Thread::Queue;

our $W ||= 3;
my( $dir, $re ) = @ARGV;
my $Q = new Thread::Queue;
my $running : shared = 0;

sub worker {
    $running++;
    sleep 1;
    while( $Q->pending ) {
        my $file = $Q->dequeue;
        print "Processed $file";
    }
    $running--;
}
$Q->enqueue( grep{ m[$re] } glob "$dir/*" );
threads->new( \&worker )->detach for 1 .. $W;
sleep 1 while $running < $W;
sleep 1 while $running;
__END__
[ 1:55:22.37] P:\test>419115 . htm$
Processed ./370949.htm
Processed ./376142.htm
Processed ./377082db.htm

[ 1:55:31.92] P:\test>419115 data dat$
Processed data/1mb.dat
Processed data/1millionlines.dat
Processed data/5mb.dat
Processed data/bin.dat
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