Ah so, Well lets just put down everything.

[root@perlbox sandbox]# ls
file1.pl  file2.pl  memory
[root@perlbox sandbox]# cat memory
XXXXXXXXXXXXXxxxxXxXXXXXXX


[root@perlbox sandbox]# cat file1.pl
 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);
[root@perlbox sandbox]# perl file1.pl
[root@perlbox sandbox]# cat memory
XXXXXXXXXXXXXxxxxXxXXXXXXX


[root@perlbox sandbox]#
[download]

So as you see it doesn't write to the memory file, while I would have guessed it would have write down some numbers, Since of..

 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;++$i) { <b>$mmap = $i;</b> sync($mmap,1);
+ }
 unmap ($mmap);
[download]

the Bold code.
Already thanks a lot. Is this the information required?