[question] Execute system command and lua command successively

[jaysonwillson]

Hello.
I have the following situation in my rc.lua -- I have special keybinds for changing volume or turning it off, they use "amixer". I also need to update my volume widget's information after every execution of such command. I update volume widget's information using update_volume(volume_widget) lua command, which is provided by volume widget itself.

I tried the following configuration:
function ()
awful.util.spawn("amixer set Master 4%+ on")
update_volume(volume_widget)
end)

But I met a problem: volume widget is updated faster, than volume changes, so its information is not correct.

I have also tried the following two methods:

local f = io.popen("amixer set Master 4%+ on")
f:close()
update_volume(volume_widget)

and

os.execute("amixer set Master 4%+ on")
update_volume(volume_widget)

They both work fine, and update_volume runs just after "amixer" finishes its execution.
But one man has said, that when I use such commands as io.popen;close and os.execute, the whole Awesome freezes and waits, until "amixer" command finishes its execution. Is it so?

If it is, could you please recommend me, how should I implement the following: "Run lua command just after system command finishes its execution" in a correct way? I know that I can run "amixer ... && echo "update_volume(volume_widget)" | awesome-client", but it seems to be a slow and ungraceful solution.

[psychon]

It's not the best API, but we now have awful.spawn.with_line_callback("amixer, set Master 4%+ on", function() end(), function() end, function() update_volume(volume_widget) end). This needs those "empty functions" to work correctly. Hm....