1 / 35

Parallel and Concurrent Programming in Haskell

Parallel and Concurrent Programming in Haskell. Satnam Singh Microsoft Research Cambridge. Leeds2009. Recap. par :: a -> b -> b pseq :: a -> b -> b forceList :: [a] -> () x ` par ` (y ` pseq ` x+y ) Determinisim. a. b. c. d. l. f a. f b. f c. f d. map f l.

altessa
Download Presentation

Parallel and Concurrent Programming in Haskell

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Parallel and Concurrent Programming in Haskell Satnam Singh Microsoft Research Cambridge Leeds2009

  2. Recap • par :: a -> b -> b • pseq :: a -> b -> b • forceList :: [a] -> () • x `par` (y `pseq` x+y) • Determinisim

  3. a b c d l f a f b f c f d map f l map :: (a -> b) -> [a] -> [b] map f [] = [] map f (x:xs) = f x : map f xs

  4. 3 1 7 2 l 6 2 14 4 map double l double :: Int -> Int double x = 2 * x

  5. a b c d l f a f b f c f d parMap f l parMap :: (a -> b) -> [a] -> [b] parMap f [] = [] parMap f (x:xs) = fx `par` (fx : parMap f xs) where fx = f x

  6. a b c d l f a f b f c f d parMap f l parMap :: (a -> b) -> [a] -> [b] parMap f [] = [] parMap f (x:xs) = fx `par` (fxs `pseq` (fx:fxs)) where fx = f x fxs= parMap f xs

  7. a b c d l f a f b f c f d parMap f l parList :: Strategy a -> Strategy [a] parListstrat [] = () parListstrat (x:xs) = strat x `par` (parListstratxs) parMap:: Strategy b -> (a -> b) -> [a] -> [b] parMapstrat f xs = map f xs `using` parListstrat

  8. Explicitly Creating Threads • forkIO :: IO () -> ThreadID • Creates a lightweight Haskell thread, not an operating system thread.

  9. Inter-thread Communication • putMVar :: MVar a -> IO () • takeMVar :: MVar a -> IO a

  10. MVars empty 52 mv ... putMVarmv 52 ... ... ... ... v <- takeMVarmv ...

  11. Rendezvous threadA threadB send 42 42 read 42 blocked send 84 read 84 and continue

  12. Rendezvous threadA :: MVarInt -> MVar Float -> IO () threadAvalueToSendMVarvalueReceivedMVar = do -- some work -- new perform rendezvous by sending 42 putMVarvalueToSendMVar 42 -- send value v <- takeMVarvalueToReadMVar putStrLn (show v)

  13. Rendezvous threadB :: MVarInt -> MVar Float -> IO () threadBvalueToReceiveMVarvalueToSendMVar = do -- some work -- now perform rendezvous by waiting on value z <- takeMVarvalueToReceiveMVar putMVarvalueToSendMVar (2 * z) -- continue with other work

  14. Rendezvous main :: IO () main = do aMVar <- newEmptyMVar bMVar <- newEmptyMVar forkIO (threadAaMVarbMVar) forkIO (threadBaMVarbMVar) threadDelay 1000 -- BAD!

  15. A function that does some work fib :: Integer -> Integer fib 0 = 0 fib 1 = 1 fib n = fib (n-1) + fib (n-2)

  16. Asynchronous Call fibThread :: Int -> MVarInt -> IO () fibThread n resultMVar = putMVarresultMVar (fib n) resultMVar <- newEmptyMVar forkIO (fibThread30resultMVar) seq (fib 30) (return ()) result <- takeMVarresultMVar

  17. $ time fibForkIO +RTS -N1 real 0m40.473s user 0m0.000s sys 0m0.031s $ time fibForkIO +RTS -N2 real 0m38.580s user 0m0.000s sys 0m0.015s

  18. putMVarresultMVar (fib 30) resultMVar resultMVar 83204 fib 30 thunk for computing fib 30

  19. Exercise: fix fibThread

  20. Inter-thread Communication 2 • putTVar:: TVara -> STM() • takeTVar:: TVara -> STM a • atomically :: STM a -> IO a

  21. TVars empty 52 tv ... atomically (putTVarmv52) ... ... ... ... v <- atomically (takeTVarmv) ...

  22. retry do v <- readTVar bal if v< 10 then retry else writeTVar bal (v-10)

  23. Reading the first arrival... q2 q1 atomically (doi<- “readTVar q1 or if q1 empty readTVarq2” ; writeTVar r i ) r

More Related