[mythtv] Myth calls external channel change script for two inputs simultaneously

[Stephen Davies]

Hi,

I have two pvr250 cards, connected to a "dual channel" satellite
receiver.  I use lirc to change channels.

I was wondering why Myth occasionally recorded the wrong channel,
until I noticed that if you schedule two recordings for the exact same
time, then "exact same time" really means that and you end up with two
copies of the change-channel script running at the same time.

I fixed the problem by having my script make and release a lock file:

  echo $$ >/var/lock/changechannel.lock.$$
  while ! ln /var/lock/changechannel.lock.$$ /var/lock/changechannel.lock; do
    sleep 1
  done
  ...do lirc send_once stuff...
  rm /var/lock/changechannel.lock.$$ /var/lock/changechannel.lock


I can provide a patch for the contributed channel change examples, or
alternatively Myth itself could use a lock to avoid two channel
changes running at the same time?

Thanks,
Steve