#!/usr/bin/perl -Tw 
 
use strict;
use Fcntl (':flock');

....

sub DeleteRecords {

    no strict 'subs'; # strict does not like O_EXCL and O_CREAT??
    my($file, @delete_these) = @_;
    # avoid race conditions, where subscriber.txt is changed between
    # reading contents with &GetRecords and writing new subscriber 
    # list with &SetRecords. We create a lockfile only if it does
    # not already exist ie no other process performing &DeleteRecords
    my $count = 0;
    until (sysopen (LOCK, "$path_to_files/lockfile.txt", O_EXCL | O_CREAT | O_WRONLY)) {
        sleep 1;
        DieNice("Can't create lockfile '$path_to_files/lockfile.txt': $!\n") if ++$count >= $timeout;
    }
    my @records = &GetRecords($file);
    for my $record (@delete_these) {
        @records = grep{ $_ ne $record }@records;
    }
    &SetRecords($file, @records);
    close LOCK;
    unlink "$path_to_files/lockfile.txt" or DieNice("Can't unlink lockfile: $!\n");
  return;
}