Dear monks,

I am trying to synchronise two processes (recording and playback) so that I can be reasonably certain that each begins at a similar time to the other---after any necessary initialisation required for each. I have tried to do this with threads, using a number of signalling schemes, however something is going wrong and I was wondering if anybody had a quick solution. Alternatively, perhaps there is a better way to achieve the same goal.

Here is a mockup:

sub player {
  # ... Initialisation code ... 
  {
    lock $counter;
    ++$sig_counter;
    cond_wait( $sig_counter ) until $sig_counter == 3;
  }
  # ... Playing code ...
}

sub recorder {
  # ... Initialisation code ...
  {
    lock $counter;
    ++$sig_counter;
    cond_wait( $sig_counter ) until $sig_counter == 3;
  }
  # ... Recording code ...
}

$sig_counter = 0;
$player_thread   = threads->create( \&player );
$recorder_thread = threads->create( \&recorder );
{ # This block should wait for threads to init
  lock $sig_counter;
  cond_wait( $sig_counter ) until $sig_counter == 2;
}
{ # This block should signal subs to start main code
  lock $sig_counter;
  ++$sig_counter;
}
[download]

I've also tried similar things with explicit cond_signal for each state instead of the counter (i.e. player_ready, recorder_ready, all_go, etc.), but everything stops once the threads are done initialising and signalling to the 'parent'.

Best regards, Jason

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