Lua execute several tasks at once

Question

I have been looking for a solution to execute several task (atleast 2) simultaneously. I found something like coroutines in lua. Can anybody please clarify me in detail how to handle 2 or more than one task? Basically what I am trying to do is to run execute some event and measure the memory consumption for that process using lua script. Any quick solution or ideas would be highly appreciated. Thanks

Answer 1

Take a look a io.popen(prog [, mode]).

From the documentation for io.popen, it "starts prog in an other process".

Here is how I would implement this:

-- launch the prog you want to measure. I assume it does not quit immediately.
-- lua will not block here: it does not wait for prog to exit.
io.popen('script-you-want-to-measure')

-- launch the second process to measure the first.
local measure = io.popen('measuring-process', 'r')

-- read all will block until the measure program exits
local measure_output = measure:read('*a')
f:close()

-- do what you want with the output

Answer 2

I don't know if this can help:

-- task-like example --

local tasks = {  } -- queue

local task = coroutine.wrap -- alias

local function suspend ( )
  return coroutine.yield (true)
end

local function shift (xs)
  return table.remove (xs, 1) -- removes the first element
end

local function push (xs, x)
  return table.insert (xs, x) -- inserts in the last position
end

local function enqueue (f)
  return push (tasks, task (f))
end

-- begin to run the tasks --
local function start ( )
  local curr
  while #tasks > 0 do -- while the tasks queue isn't empty
    curr = shift (tasks)
    if curr ( ) then push (tasks, curr) end -- enqueue the task if still alive
  end
end

-- create a task and begin to run the tasks --
local function spawn (f)
  local curr = task (f) --
  if curr ( ) then push (tasks, curr) end
  return start ( )
end

-- adds task to tasks queue --
enqueue (function ( )
  for i = 1, 3 do
    print ("Ping. <<", i)
    -- os.execute "sleep 1" -- uncomment if you're using *nix
    suspend( )
  end
end)

-- yet another task --
enqueue (function ( )
  for i = 1, 5 do
    print "..."
    suspend( )
  end
end)

-- begins to run the tasks --
spawn (function ( )
  for i = 1, 5 do
    print ("Pong. >>", i)
    -- os.execute "sleep 1" -- uncomment if you're using *nix
    suspend( )
  end
end)

-- end of script --