1. chdir isn't unique to each thread. If you chdir in one thread they all change.
2. changing to fork would allow chdir per fork because the memory is copied when forked
3. This is an excellent point. You can't pass the full path to put but, you can pass a file handle.

Here is the updated code:

sub worker {
   my $tid = threads->tid;
   my( $Qwork, $Qresults ) = @_;

   my $ftp = Net::FTP->new($gFtpServer, Debug => 0);
   $ftp->login($gFtpUser, $gFtpPass) or print "unable to loging to $gF
+tpServer: $ftp->message\n";

   while(my $work = $Qwork->dequeue) {
      my ($result, $localFile);
      my (@workItem);

      @workItem = split (",", $work);

      chomp($workItem[0]);
      chomp($workItem[1]);
      chomp($workItem[2]);
      print "ftp dir: $workItem[0]\n";
      print "local dir: $workItem[1]\n";
      print "file: $workItem[2]\n";
      $localFile = sprintf("%s%s",$workItem[1],$workItem[2]);

      open (my $fh, "<", $localFile) or print "unable to open file";
      $ftp->cwd($workItem[0]) or print "unable to FTP change dir $work
+Item[0]: $ftp->message\n";
      $ftp->put($fh, $workItem[2]) or print "unable to FTP $workItem[2
+]: $ftp->message\n";
      ## Process $work to produce $result ##
      $result = "$tid : result for workitem ";
      $Qresults->enqueue( $result );
   }
   $Qresults->enqueue( undef ); ## Signal this thread is finished
   $ftp->quit;
}
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