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Concurrency demos

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[[Category:Tutorials]]
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This page collects examples of concurrent and parallel programming in Haskell.
[[Category:Code]]
 
   
A large range of small demonstration programs for using concurrent and
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== 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 ==
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* [[/Zeta |Riemann's Zeta function approximation]]
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* [[/Graceful exit|Signal that you want to gracefully exit another thread]]
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* [[/Two reader threads|Passing messages across a single chan to two readers]]
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* [[Implement a chat server|Chat server - using a single channel for a variable number of readers]]
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* [[/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.
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== More examples ==
   
<haskell>
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A large range of small demonstration programs for using concurrent and
import Control.Concurrent
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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 :: (Floating (Complex a), RealFloat a, Integral b) => Complex a -> (b, b) -> Complex a
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== Proposed updates ==
zetaRange s (x,y) = sum [ (fromIntegral n :+ 0) ** (-s) | n <- [x..y] ]
 
   
cut :: (Integral a) => (a, a) -> a -> [(a, a)]
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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 = []
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== Other examples ==
cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size')
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* [[/Haskell-Javascript concurrency|Haskell -> Javascript: Pseudo-concurrent threads in web browser]]
   
getParams :: IO (Int, Int, Complex Double)
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[[Category:Parallel]]
getParams = do
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[[Category:Tutorials]]
argv <- getArgs
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[[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>
 

Latest revision as of 16:18, 16 March 2011

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

Contents

[edit] 1 Examples

[edit] 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
MVars
and
forkIO
.

[edit] 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.

[edit] 4 Other examples