BoundedChan (empty) → 1.0.0.0

raw patch · 3 files changed

+99/−0 lines, 3 filesdep +arraydep +basesetup-changed

Dependencies added: array, base

Files

• BoundedChan.cabal +20/−0
• Control/Concurrent/BoundedChan.hs +77/−0
• Setup.hs +2/−0

@@ -0,0 +1,20 @@+name:       BoundedChan+category:   Concurrency+version:    1.0.0.0+license:    BSD3+author:     Adam Wick <awick@galois.com>+maintainer: Adam Wick <awick@galois.com>+stability:  stable+build-type: Simple+cabal-version: >= 1.6+tested-with: GHC ==6.10+synopsis:      Implementation of bounded Chans.+description:   This library introduces BoundedChan. BoundedChan works exactly+               like Chan -- and, indeed, has the exact same interface -- but+               is guaranteed to operate in a bounded amount of space.++Library+  build-depends: base >= 3, array+  exposed-modules: Control.Concurrent.BoundedChan+  GHC-Options: -O2 -Wall -funbox-strict-fields+

@@ -0,0 +1,77 @@+-- |Implements bounded channels. In these channels, you can give a+-- rough maximum number of elements, and you will be guaranteed that no more+-- than that number of elements will be pending within the channel.+--+-- This boundedness is ideal when you will be (or may be) writing to a channel+-- faster than you are able to read from it.+--+-- This module supports all the functions of Control.Concurrent.Chan except+-- unGetChan and dupChan, which are not supported for bounded channels.+module Control.Concurrent.BoundedChan(+         BoundedChan+       , newBoundedChan+       , writeChan+       , readChan+       , isEmptyChan+       , getChanContents+       , writeList2Chan+       )+  where++import Control.Concurrent.MVar+import Control.Monad(replicateM)+import Data.Array+import System.IO.Unsafe(unsafeInterleaveIO)++-- |BoundedChan is an abstract data type representing an unbounded channel.+data BoundedChan a = BC {+       _size     :: Int+     , _contents :: Array Int (MVar a)+     , _writePos :: MVar Int+     , _readPos  :: MVar Int+     }+-- LOCK ORDERING: A -> B -> C++-- |Create a new bounded chan with size n. +newBoundedChan :: Int -> IO (BoundedChan a)+newBoundedChan x = do+  entls   <- replicateM x newEmptyMVar+  wpos    <- newMVar 0+  rpos    <- newMVar 0+  let entries = listArray (0, x - 1) entls+  return (BC x entries wpos rpos)++-- |Write an element to the channel. If the channel is full, this routine will+-- block until it is able to write. If you have multiple writers, be careful+-- here, because the unlocking is not guaranteed to avoid starvation.+writeChan :: BoundedChan a -> a -> IO ()+writeChan (BC size contents wposMV _) x = do+  wpos <- takeMVar wposMV+  putMVar wposMV $! (wpos + 1) `mod` size+  putMVar (contents ! wpos) x++-- |Read an element from the channel. If the channel is empty, this routine +-- will block until it is able to read.+readChan :: BoundedChan a -> IO a+readChan (BC size contents _ rposMV) = do+  rpos <- takeMVar rposMV+  putMVar rposMV $! (rpos + 1) `mod` size+  takeMVar (contents ! rpos)++isEmptyChan :: BoundedChan a -> IO Bool+isEmptyChan (BC _ contents _ rposMV) = do+  rpos <- takeMVar rposMV+  res <- isEmptyMVar (contents ! rpos)+  putMVar rposMV rpos+  return res++getChanContents :: BoundedChan a -> IO [a]+getChanContents ch = unsafeInterleaveIO $ do+                       x  <- readChan ch+                       xs <- getChanContents ch+                       return (x:xs)++-- |Write a list of elements to the channel. Note that this may block as it+-- writes the list into the channel.+writeList2Chan :: BoundedChan a -> [a] -> IO ()+writeList2Chan ch ls = mapM_ (writeChan ch) ls

@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain