Cannot return functions in async methods

[svermeulen]

Using the implementation here, you cannot create async functions that return functions, since the returned functions will always be interpreted as a 'thunk'. I attempted to modify the pong method to allow this. In case it's useful to others, I wanted to share what I'm using instead:

local pong = function (func, callback)
  assert(type(func) == "function", "Expected type func but found " .. type(func))
  local thread = co.create(func)
  local step = nil
  step = function (...)
    local go, ret = co.resume(thread, ...)
    assert(go)
    if co.status(thread) == "dead" then
      if callback then
        callback(ret)
      end
    else
      assert(type(ret) == "function")
      ret(step)
    end
  end
  step()
end

This allows function return values because it always calls the callback value when the coroutine is dead. Also, I think we can assume that the go value is always true now that we are checking the co.status immediately after the call to resume

[ms-jpq]

Thank you!

Really good catch, but by the looks of it doing this will swollow errors from coroutines.

When I have more time Ill try to figure out how to make it all work nicely :D

Sorry Ill leave this issue hanging for a bit, brain is foggy right now

[ms-jpq]

Also you are from halifax!

ohhhhhhhhh canada, our home and native land.

Go Canada!

[svermeulen]

Haha, yes, I see you are a fellow canadian as well :)

Yes, you are correct. I realize now that go will be false when exceptions occur. I've now modified it to this instead:

local pong = function (func, callback)
  assert(type(func) == "function", "Expected type func but found " .. type(func))
  local thread = co.create(func)
  local step = nil
  step = function (...)
    local go, ret = co.resume(thread, ...)
    assert(go, "Async function failed! Details: " .. ret)
    if co.status(thread) == "dead" then
      if callback then
        callback(ret)
      end
    else
      assert(type(ret) == "function")
      ret(step)
    end
  end
  step()
end

[ms-jpq]

i have update the code, thank you.

also added you to the read me #thank section 👍

local async_tasks_2 = function (val)
  return a.sync(function ()
    -- await all
    local w, z = a.wait_all{e2(val, val + 1), e2(val + 2, val + 3)}
    print(unpack(w))
    print(unpack(z))
    return function ()
      return 4
    end
  end)
end

the example code works with func returns