diff --git a/Control/Concurrent/Chan/Forwardable.hs b/Control/Concurrent/Chan/Forwardable.hs new file mode 100644 --- /dev/null +++ b/Control/Concurrent/Chan/Forwardable.hs @@ -0,0 +1,106 @@ +{- | A concurrent FIFO queue which behaves like Base's Chan with the new added 'forward' primative + for merging two channels. Unlike duplicate style merging, when two channels are forwarded to each other, + writes to one channel will not be duplicated to both channels, rather it will be as if both channels contents + had been merged and all their outstanding and future references now point to this new channel. + + See for futher specification. + -} +module Control.Concurrent.Chan.Forwardable ( Chan() + , newChan + , writeChan + , readChan + , forwardChan + , getChanContents + , writeList2Chan + ) where + +import Control.Concurrent.Chan.Forwardable.Internals + +import qualified Control.Concurrent.Chan.Unagi as U +import Data.IORef +import Data.Typeable +import Control.Concurrent (forkIO) +import GHC.Base (join) +import System.IO.Unsafe ( unsafeInterleaveIO ) + +-- | Create a new channel +newChan :: IO (Chan a) +newChan = do + (ci,co) <- U.newChan + mi <- newIORef ci + to <- newIORef co + return $ Chan mi to + +{- | Write a value to the channel. + +If the channel becomes forwarded +at any time in the future, any thread +waiting on a value from the forwarded +channel may receive this value. +-} +writeChan (Chan mi _) v = do + ci <- readIORef mi + U.writeChan ci $ return v + +{- | Read a value from a channel. + +If a thread is waiting at a readChan +and another thread forwards this channel +to another (or visa versa) and the other +channel contains elements, this read might +now consume that element. +-} +readChan (Chan mi to) = join $ readIORef to >>= U.readChan + +{- | Forward takes two channels and makes them act as one. +It obeys a few properties: + +* /Commutivity/: @'forwardChan' a b === 'forwardChan' b a@ + +* /Behavioral Transitivity/: @('forwardChan' a b >> 'forwardChan' b c) === ('forwardChan' a b >> 'forwardChan' a c)@ + +* /Equal Opportunity/: A write to either channel before or after the forward will be able to be consumed by a read on either of the channels, and +there will be no unexpected starvation or race conditions. + +* /Early Bird Gets The Worm/: The first thread to read from either channel will, after a 'forward', always recieve +the next available item. Similarly, items written to either channel are read in the same order they were written in. + +* /Note/: if @a '==' b@ is @False@, then after @'forwardChan' a b@ will not cause @a '==' b@ to become @True@. + +-} +forwardChan :: Chan a -> Chan a -> IO () +forwardChan c@(Chan mi to) (Chan mi' to') = do + ci' <- readIORef mi + atomicWriteIORef mi' =<< readIORef mi + + co' <- readIORef to' + atomicWriteIORef to' =<< readIORef to + + let readIfAvailable av non = do + (v,_) <- U.tryReadChan co' + v <- U.tryRead v + case v of + Just _ -> av =<< join (U.readChan co') + _ -> non + + getOldOrNew = readIfAvailable return $ readChan c + + useAll :: IO () + useAll = readIfAvailable (\v -> writeChan c v >> useAll) $ return () + + useAll + U.writeChan ci' $ getOldOrNew -- executes if we're stuck on a read. + + + + +-- | Return a lazy list representing the contents of the supplied 'Chan' +getChanContents :: Chan a -> IO [a] +getChanContents ch = unsafeInterleaveIO $ do + x <- readChan ch + xs <- getChanContents ch + return $ x:xs + +-- | Write an entire list of items to a 'Chan'. +writeList2Chan :: Chan a -> [a] -> IO () +writeList2Chan ch ls = sequence_ (map (writeChan ch) ls) diff --git a/Control/Concurrent/Chan/Forwardable/Internals.hs b/Control/Concurrent/Chan/Forwardable/Internals.hs new file mode 100644 --- /dev/null +++ b/Control/Concurrent/Chan/Forwardable/Internals.hs @@ -0,0 +1,14 @@ +module Control.Concurrent.Chan.Forwardable.Internals where + +import qualified Control.Concurrent.Chan.Unagi as U +import Data.IORef +import Data.Typeable + +-- | A forwardable channel. +-- It supports all the standard channel operations +-- as layed out in the base library (as of 4.10.0.0) +-- except 'dupChan' +data Chan a = Chan { inChan :: IORef (U.InChan (IO a)), -- ^ a reference to an in-channel of actions that output the value. Warning: custom playing with these internals is likely to break forward's nice properties. + outChan :: IORef (U.OutChan (IO a)) -- ^ a reference to an out-channel of actions that output the value. + } + deriving (Eq, Typeable) diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. 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