Concurrency demos

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-	[[Category:Tutorials]]	+	This page collects examples of concurrent and parallel programming in Haskell.
-	[[Category:Code]]	+
-	A large range of small demonstration programs for using concurrent and	+	== Examples ==
-	parallel Haskell are in the Haskell [http://darcs.haskell.org/testsuite/tests/ghc-regress/concurrent/should_run/ concurrency regression tests]. In particular, they show the use of <hask>MVars</hask> and <hask>forkIO</hask>.	+
-	== A simple example of parallelism in Haskell ==	+	* [[/Zeta |Riemann's Zeta function approximation]]
		+	* [[/Graceful exit|Signal that you want to gracefully exit another thread]]
		+	* [[/Two reader threads|Passing messages across a single chan to two readers]]
		+	* [[Implement a chat server|Chat server - using a single channel for a variable number of readers]]
		+	* [[/Simple producer and consumer|Passing IO events lazily from a producer to a consumer thread]]
-	This little piece of code computes an approximation of Riemann's zeta function, balancing the work to be done between N threads.	+	== More examples ==
-	<haskell>	+	A large range of small demonstration programs for using concurrent and
-	import Control.Concurrent	+	parallel Haskell are in the Haskell [http://darcs.haskell.org/testsuite/tests/ghc-regress/concurrent/should_run/ concurrency regression tests]. In particular, they show the use of <hask>MVars</hask> and <hask>forkIO</hask>.
-	import Control.Concurrent.MVar	+
-	import Control.Monad	+
-	import Data.Complex	+
-	import System.Environment	+
-	zetaRange s (x,y) = sum [ (fromIntegral n :+ 0) ** (-s) | n <- [x..y] ]	+	== Proposed updates ==
-	cut :: (Integral a) => (a, a) -> a -> [(a, a)]	+	The base 3.0.3.1 package's Control.Concurrent.QSem and QSemN are not exception safe. The [[SafeConcurrent]] has the proposed replacement code.
-	cut (x,y) n = (x, x + mine - 1) : cut' (x + mine) size (y - mine)	+
-	where	+
-	(size, modulo) = y `divMod` n	+
-	mine = size + modulo	+
-	cut' _ _ 0 = []	+	== Other examples ==
-	cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size')	+	* [[/Haskell-Javascript concurrency|Haskell -> Javascript: Pseudo-concurrent threads in web browser]]
-	getParams :: IO (Int, Int, Complex Double)	+	[[Category:Parallel]]
-	getParams = do	+	[[Category:Tutorials]]
-	argv <- getArgs	+	[[Category:Code]]
-	case argv of	+
-	(t:n:s:[]) -> return (read t, read n, read s)	+
-	_ -> error "usage: zeta <nthreads> <boundary> <s>"	+
-		+
-	main :: IO ()	+
-	main = do	+
-	(t, n, s) <- getParams	+
-	childs <- zipWithM thread (repeat s) (cut (1, n) t)	+
-	results <- mapM takeMVar childs	+
-	print (sum results)	+
-	where	+
-	thread s range = do	+
-	putStrLn ("Starting thread for range " ++ show range)	+
-	mvar <- newEmptyMVar	+
-	forkIO (putMVar mvar (zetaRange s range))	+
-	return mvar	+
-	</haskell>	+

---

Current revision

This page collects examples of concurrent and parallel programming in Haskell.

Contents 1 Examples 2 More examples 3 Proposed updates 4 Other examples

1 Examples

• Riemann's Zeta function approximation
• Signal that you want to gracefully exit another thread
• Passing messages across a single chan to two readers
• Chat server - using a single channel for a variable number of readers
• Passing IO events lazily from a producer to a consumer thread

2 More examples

A large range of small demonstration programs for using concurrent and

parallel Haskell are in the Haskell concurrency regression tests. In particular, they show the use of and .

3 Proposed updates

The base 3.0.3.1 package's Control.Concurrent.QSem and QSemN are not exception safe. The SafeConcurrent has the proposed replacement code.

4 Other examples

• Haskell -> Javascript: Pseudo-concurrent threads in web browser

Categories: Parallel | Tutorials | Code