Hello, I have a CGI that forks some processing of a set of files to a remote host via ftp.
I have to retrieve by ftp the result of this processing (one file for each file submitted) with a cron process. The list of files to be retrieved is written by the CGI in the $log file below. The processing can be delayed and some submissions might take place while I'm retrieving some results with the cron process (i.e. the CGI execution and the cron process are totally independent). I came up with the following, but I'm definitely not sure if this is robust enough.
Any kind suggestion ?
Thank you.

use strict;
use warnings;
use Net::FTP;

    my @files_submitted;
    my @files_to_retrieve;

    # Cron procedure to retrieve from a remote host
    # a set of files that were sent there for processing

    my ($host,$user,$pass) = ('my_host','user','passwd');
    my $log = './logfile.log'; 
    my $tmp_log = './logfile.tmp';
    my $working_log = './logfile.wrk';
    my $lock = './lockfile.lock';
    my $dir = './tmp';

    # See if there is a lock still active from 
    # previous execution of this script (it might
    # be still active, quit in that case)
    if (-e $lock) {
        open FH, "<$lock" or die "Can't open $lock: $!\n";
        my $pid = <FH>;
        print "pid $pid \n";
        close (FH);
        exit unless (kill 0 => $pid);
    }

    # Create a new lock
    open FH, ">$lock" or die "Can't open $lock: $!\n";
    print FH getppid."\n";
    close (FH);

    # $working_log will contain the list of files to be
    # retrieved. It can exist if a previous execution 
    # went bad or if the files on the remote host were
    # not ready when this script was executed the 
    # previous time
    if (-e $working_log) {
        open FH, "<$working_log" or 
             die "Can't open $working_log: $!\n";
        while (<FH>) {
           chomp;
           push @files_to_retrieve,$_;
        }
        close (FH);
    }
    # See if there are also new files that need
    # to be retrieved
    if (-e $log) {
        # Move the log to avoid interference with files
        # that could have been submitted between this
        # execution and the previous one
        system "mv $log $tmp_log";
        open FH, "<$tmp_log" or 
                 die "Can't open $tmp_log: $!\n";
        while (<FH>) {
           chomp;
           push @files_to_retrieve,$_;
        }
    }
    # Check if nothing has to be done
    goto REMOVE_LOCK unless (@files_to_retrieve);

    # Loop on the files and process them
    my @todo = (@files_to_retrieve);
    my @done;
    my $ftp = Net::FTP->new($host, Debug => 0);
    $ftp->login($user,$pass) or 
          die "Cannot login ", $ftp->message;
    $ftp->cwd($dir);
    $ftp->binary();
    foreach (@files_to_retrieve) {
       $ftp->get($_) or next;
       push @done, shift(@todo);
    }
    $ftp->quit;

    # Remove the temporary log
    system "rm $tmp_log";

    # Rewrite the working log if anything went wrong
    # or some files were not ready
    if (@todo) {
        open FH, ">$working_log" or 
                 die "Can't open $working_log: $!\n";
        foreach (@todo) {
           print FH $_."\n";
        }
        close (FH);
    }

    # Remove lock

    REMOVE_LOCK:
    system "rm $lock";
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