Thanks for the report. Its been a while since I tested it. I just ran it a few times myself, and am getting similar failures. I'll work at it and report any fixes I can find.

Update: I believe it is a locking problem, as I try to lock a hash acting as a container variable, as in lock $track{$tr}{'go'};

I was counting on each track to have it's own shared variable, so I thought locking would not be a problem. It didn't seem to matter on a single cpu computer, but now I have a multi-core computer, and it matters. Furthermore, I thought I could lock a portion of the shared hash container %track, but I read in perldoc threads::shared that it causes errors.

From perldoc threads::shared:

 You cannot lock the individual elements of a container variable:

             my %hash :shared;
             $hash{'foo'} = 'bar';
             #lock($hash{'foo'});          # Error
             lock(%hash);                  # Works

           If you need more fine-grained control over shared variable 
+access, see Thread::Semaphore.
[download]

So it seems this code needs a re-write to make locking work.