Add a reload command

[smimram]

This feature was requested on the ML:

Addition for system, a reload command which shuts down everything, (re)loads the running script and runs again. This makes reloading possible on the liquidsoap level rather than the OS level.

[dbaelde]

If possible, I'd like this to be done from outside liquidsoap (have an
external script ask liquidsoap to shutdown, and reload it) rather than
clutter our main.ml file, unless there is a good reason for it.

[smimram]

Well, it would be nice to have it in Liquidsoap (in the standard library). It could be implemented by invoking suitable external command, and we should have the name of the script in argv.(0). It would be nice if we code it plainly in utils.liq, without requiring an external script.

[dbaelde]

Yes, utils.liq is no problem for me, I was just begging that we don't
change the ML code.

[mkonecny]

This would be very nice! 👍

[smimram]

I came up with something like this:

# Restart the currently running script.
def restart() =
  relaunch = "liquidsoap #{argv(0)} #{argv(1)} #{argv(2)} #{argv(3)}"
  # print("relaunch command: #{relaunch}")
  cmd = "{ while `ps -p #{getpid()} > /dev/null`; do sleep 1; done; echo \"Liquidsoap died\"; #{relaunch}; }&"
  system(cmd)
  shutdown()
end

It does not work (yet) but it might be a good starting point of an implementation without deep modifications of Liquidsoap.

[mkonecny]

Interesting, but that would be *nix dependent no? Or are you guys running in cygwin with your Windows port?

[smimram]

This was just a try to implement this purely in Liquidsoap. However I am not really convinced by this way or proceeding. I think I'll try to make a new builtin command, which moreover would be more portable...

[mkonecny]

This would actually be really useful for us, since I am currently running one of Airtime's background processes as root only only because restart requires calling init.d scripts.

BTW a small nit-pick. I first assumed this feature was related to allowing Liquidsoap to continue running while "reloading" its config files. Perhaps this should be called "restart".

[asantoni]

What is the use case for "shutting down everything"?

Wouldn't a reload command be much more useful if it didn't interrupt playback? How is Liquidsoap supposed to be used for broadcasting if reconfiguration requires dead air?

[dbaelde]

@asantoni Given the richness of liquidsoap scripts it is not generally feasible to reload without interrupting playback. The current issue is to provide a convenient way to do the only thing that we can support in general, ie. shut down everything, read the script again, and restart asap.

In practice, people have a simple fallback for their radio (which can be setup at the icecast level, or using a simple liquidsoap script) that is never restarted, and plays an interlude when the real radio is being restarted.

[ALuserX]

That's a great feature I missed so much. I also hope it will be possible to restart via telnet.

[OFFTOPIC]BTW, @asantoni could you possibly point me to a working example of the fallback you're talking about. That would be really great.[/OFFTOPIC]

[smimram]

I tired to implement something in this direction in #135.

[smimram]

Side note, my test file is

set("log.file",false)
set("log.stdout",true)
set("log.level",5)
set("server.telnet",true)
set("init.catch_exn",false)

n = ref 0

def r(m) =
  n := !n + 1
  if !n > 1 then restart() end
end

s = playlist("~/Music")
s = on_metadata(r,s)
s = audio_to_stereo(s)
s = mksafe(s)
s = fallback([s,input.harbor("/test")])

output.pulseaudio(id="pa",s)

when you pa.skip on the telnet, it restarts! :)

[smimram]

The branch #135 has been merged. It add as restart command to Liquidsoap.

[mylselgan]

Hi, I want to restart the whole script if the main source failed and mksafe called or static emergency single called could you please give me any example here