haskellstmgloss

Haskell Gloss and STM concurrency integration

I want to update a Haskell Gloss GUI from multiple threads (4 threads). I am looking at an application where an event on the Haskell Gloss GUI triggers a series of steps that end up creating threads each of which can and should change the GUI if need be. I am using the Gloss play function.

The Gloss GUI function play of type:

play
  :: Display
     -> Color
     -> Int
     -> world
     -> (world -> Picture)
     -> (Event -> world -> world)
     -> (Float -> world -> world)
     -> IO ()

Notice the parameter (Event -> world -> world) which is the function that handles the keyboard events.

If I click say x on the keyboard, then handleKeys::Event -> world -> world captures this event, takes a world(a model of my application which is a data structure for display by Gloss) and returns a world with or without changes.

Based on the event processed by handleKeys::Event -> world -> world other threads may be spawned using forkIO :: IO () -> IO ThreadId. These spawned threads should also manipulate the world and return a world for display. That is each thread runs a function of type world->world. I would then use STM primitives for concurrency. These primitives are:

    putTMVar :: TMVar a -> a -> STM ()
    takeMVar :: MVar a -> IO a
    atomically :: STM a -> IO a
    retry :: STM a
    orElse :: STM a -> STM a -> STM a

As you can already guess, the Haskell type-checker is giving me a migraine. Is there possibility of running a Gloss application relying on STM concurrency to update the GUI without violating types?

Solution

  • you should use playIO from Graphics.Gloss.Interface.IO.Game