#!/usr/bin/perl -w
use strict;
use Fcntl qw(:DEFAULT :flock);
use Time::HiRes 'usleep';
use Devel::Peek;

open LOG, ">$$.log" or die $!;

while ( 1 ) {
   open LOCK, "lock.file" or die "lock file $!";
   die "$$ failed to get lock" unless flock(LOCK,LOCK_EX);

   # perlfaq example
   sysopen(FH, "numfile", O_RDWR|O_CREAT)  
        or die "can't open numfile: $!";
   my $num = <FH> || 0;
   chomp $num;
   seek(FH, 0, 0)  or die "can't rewind numfile: $!";
   truncate(FH, 0) or die "can't truncate numfile: $!";
   $num++;
   (print FH $num, "\n") or die "can't write numfile: $!";
   close FH              or die "can't close numfile: $!";

   print LOG "$num\t$$\n";

   close LOCK;
   usleep( 100 );
   last if $num >= 100000;
}