#!/usr/bin/perl -w

 use File::Map qw/:map lock_map sync/;
 use warnings;
 use strict;

 my $mmap = undef;
 my $file = "memory";

 map_file $mmap, $file, '+<';
  if (!defined($mmap)) { print "ERROR!!\n"; }
        for(my $i=0;$i<10000;++$i) { $mmap = $i; sync($mmap,1); }
 unmap ($mmap);