Dave Tapley wrote:
Hi again all, I could do with some design pointers for a project I'm
working on combining Haskell with a robot.
My situation is:
I read sensor data from the robot lazily a line at a time, as soon as
a line is read in my code sends out a response down a pipe.
Implemented in this fashion:
mapM_ (updateFunction myIORef) fromRobot ::IO ()
fromRobot :: String
updateFunction :: IORef -> String -> IO ()
Now I wish to update a HOpenGL window synchronously with this.
To establish this I make a new HOpenGL window & return an IORef (IO
()) which holds the actions to draw my graphics. In this fashion:
myIORef <- makeWindow
--- Above code ---
mainLoop
This can be passed to updateFunction as shown above so every time it
processes a new line from the robot is can update the graphics via the
IORef.
Because neither 'mapM_ (updateFunction myIORef) fromRobot' nor
'mainLoop' terminate I've been using 'forkIO' to split one off. This
way the lazy evaluation keeps running and then window keeps updating
itself.
This works, sort of.
I have problems because the my HOpenGL code also has magic to allow
you to change the point of view using the keyboard. But when I do I
get this after a while:
LOCK SET!
Previous intel_span.c:210
Current: intel_batchbuffer.c:63
Can anyone suggest how to resolve this "two functions which never
terminate but both share IORefs" problem?
Using IORefs in two different threads probably needs MVars [1] or TVars
(atomically :: STM a -> IO a) [2] instead, to do it safely, which are
both similar to IORefs (choose whichever interface fits your usage
better, I guess). (And using forkOS like Stefan says)
[1]
<http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurrent-MVar.html>
[2]
no documentation where it should be:
<http://www.haskell.org/ghc/docs/latest/html/libraries/stm/Control-Concurrent-STM.html>
but some documentation here:
<http://www.haskell.org/ghc/docs/latest/html/libraries/base/GHC-Conc.html#t%3ASTM>
Isaac
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