Callback in coroutines not working

Bugs
1

Am I doing something silly here that means the callback within the coroutine isn’t being called?
I don’t think it’s a garbage collection issue.

I have a feeling it may be an issue with how the callback is called when the callback is inside a coroutine?

function setup()
    
    -- Works
    print("Downloading on main thread")
    http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
        print("Main thread request done.")
    end)
    
    -- Does not work
    local co = coroutine.create(function()
        print("Downloading on coroutine thread")
        http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
            print("Coroutine request done.")
        end)
    end)
    coroutine.resume(co)
    
end

Cheers,
Steppers

2

@Steppers - is the second end bracket (IE last line in setup function) necessary ?

3

@Bri_G Yep, syntactically there’s nothing wrong with it.

4

I suspect it’s because the coroutine is dead, having done its yield. If you did get back in there, you;d get a second unexpected yield, I think.

5

Try this:

    -- Does not work
    local co = coroutine.create(function()
        print("Downloading on coroutine thread")
        http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
            print("Coroutine request done.")
        end)
    end)
    print(coroutine.status(co))
    coroutine.resume(co)
    print(coroutine.status(co))

You will find, as @RonJeffries said, that co is dead.

6

@binaryblues @RonJeffries The Coroutine is dead but I don’t think that’s the immediate cause.

This still doesn’t work even though the coroutine is just suspended instead.

function setup()
    
    -- Works
    print("Downloading on main thread")
    http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
        print("Main thread request done.")
    end)
    
    -- Does not work
    local co = coroutine.create(function()
        print("Downloading on coroutine thread")
        http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
            t = data
        end)
        coroutine.yield()
    end)
    print(coroutine.status(co))
    coroutine.resume(co)
    print(coroutine.status(co))
end

function draw()
    print(t)
end

@Simeon Is there something odd going on in the backend that would cause the callback to never be called at all?

7

the coroutine runs, it’s the data that is not return from the http request


function setup()
  t = ""
  local co = coroutine.create(function()
    print("Downloading on coroutine thread")
    http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
      print("success")
      t = data
    end, function () print("failed") end )
    --coroutine.yield()
  end)
  print(coroutine.status(co))
  coroutine.resume(co)
  print(coroutine.status(co))
end

function draw()
  print(t)
end

neither success or failed are printed

8

@skar Yeah the http callback is never called, the coroutine is fine.

9

my guess is once the coroutine runs the reference to the pass or fail functions is deleted, this must happen somewhere in the http.request function because i tested using a global reference function in pass and fail and it still does not work


-- Use this function to perform your initial setup
function setup()
  t = ""
  pass = function(data)
      print("success")
      t = data
  end
  fail = function ()
    print("failed")
  end
  local co = coroutine.create(function()
    print("Downloading on coroutine thread")
    http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", pass, fail )
    --coroutine.yield()
  end)
  print(coroutine.status(co))
  coroutine.resume(co)
  print(coroutine.status(co))
  --print("Downloading in setup")
  --http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", pass, fail )
end

function draw()
  print(t)
end

i’m also inclined to believe the issue is with .request because i use coroutine as thread to load my scenes behind a loading screen and have never seen a callback fail

10

@skar After a little more digging I believe the issue could potentially stem from native side.

When the native side calls the callback It’ll be using lua_pcall, passing in the lua_State* but by the look of it, coroutines use a different lua_State object.

@Simeon this along the right lines? I’m guessing blindly here.

11

that’s deeper than my knowledge but what i can say is if you replace http.request with something else that uses callbacks like tween it works as expected

-- Use this function to perform your initial setup
function setup()
  t = ""
  pass = function(data)
      print("success")
      t = data
  end
  fail = function ()
    print("failed")
  end
  local co = coroutine.create(function()
    --print("Downloading on coroutine thread")
    --http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", pass, fail )
    --coroutine.yield()
    tween (2, {}, {}, nil, function () print ("tween done") end)
  end)
  print(coroutine.status(co))
  coroutine.resume(co)
  print(coroutine.status(co))
  --print("Downloading in setup")
  --http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", pass, fail )
end

function draw()
  print(t)
end

you can piggy back into the tween end function and pass data there, it’s a bit of a hack but it works


-- Use this function to perform your initial setup
function setup()
  t = ""
  pass = function(data)
    print("success")
    t = data
  end
  fail = function ()
    print("failed")
  end
  local co = coroutine.create(function()
    print("Downloading on coroutine thread")
    tween (2, {}, {}, nil, function () 
      http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text",  pass, fail )
    end)

    coroutine.yield()

  end)
  print(coroutine.status(co))
  coroutine.resume(co)
  print(coroutine.status(co))
  --print("Downloading in setup")
  --http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", pass, fail )
end

function draw()
  print(t)
end
12

@skar Ah, nice find! Other than being a little unwieldy that works quite nicely for what I’m trying to do.
Cheers :smile:

13

@skar You can also see that the callback inside the tween is running on the ‘main’ coroutine too:

function setup()
    
    -- Works
    print("Downloading on main thread", coroutine.running())
    http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
        print("Main thread request done.", coroutine.running())
    end)
    
    -- Does not work
    local co = coroutine.create(function()
        print("Downloading on coroutine thread", coroutine.running())
        
        tween(0.01, {}, {}, nil, function()
            http.request("https://baconipsum.com/api/?type=meat-and-filler&paras=5&format=text", function(data)
                print("Coroutine request done.", coroutine.running())
            end)
        end).time = 0.0
    end)
    coroutine.resume(co)
end

function draw()
    print()
end