use Fcntl qw( :flock );
{
    my $ini;
    open $ini, '+<', "$path/$fname" or die $!;
    flock $ini, LOCK_EX;
    my @lines = <$ini>;
    seek $ini, 0, 0;
    print $ini edit(@lines) or die $!;
    close $ini or die $!;
}

##</code><code>##

use Fcntl;
{
    my {$in,$out);
    sysopen $out, "$path/$fname.bak",
              O_WRONLY | O_CREAT | O_EXCL | O_EXLOCK
        or sleep 1 and redo;
    open $in, '<', "$path/$fname" or die $!;
    flock $in, LOCK_EX;
    while (<$in>) {
        # edit operations to modify or skip $_
        print $out or die $!;
    }
    close $in;
    close $out or die $!
    rename "$path/$fname.bak", "$path/$fname" or die $!;
}