forkable-monad (empty) → 0.1

raw patch · 4 files changed

+201/−0 lines, 4 filesdep +basedep +mtlsetup-changed

Dependencies added: base, mtl

Files

• Control/Concurrent/Forkable.hs +111/−0
• LICENSE +30/−0
• Setup.hs +3/−0
• forkable-monad.cabal +57/−0

@@ -0,0 +1,111 @@+-- Copyright 2010 Google Inc.+--+-- Author: David Anderson <dave@natulte.net>+--+-- See LICENSE and forkable-monad.cabal for authorship and licensing+-- information.++-- | This module defines a generic version of @Control.Concurrent@'s+-- 'C.forkIO', which can directly run some complex monadic actions as+-- well as plain 'IO' actions.+--+-- @Control.Concurrent@'s 'C.forkIO' accepts an 'IO' computation only,+-- and requires the caller to reconstruct the full monadic stack by+-- hand in the new thread. In contrast, this module's 'forkIO' runs a+-- computation in the same monad as the parent thread, transparently+-- transplanting the monad stack to the new thread.+--+-- For example, the following code which uses @Control.Concurrent@'s+-- 'C.forkIO':+--+-- > type MyMonad = ReaderT Int (StateT String IO)+-- >+-- > forkAndDo :: MyMonad ThreadId+-- > forkAndDo = do+-- >     r <- ask+-- >     s <- lift get+-- >     liftIO $ forkIO $ (runStateT (runReaderT forkedDo r) s >> return ())+-- >+-- > forkedDo :: MyMonad ()+-- > forkedDo = liftIO $ putStrLn "forkedDo running"+--+-- can be reexpressed with this module's 'forkIO' as:+--+-- > type MyMonad = ReaderT Int (StateT String IO)+-- >+-- > forkAndDo :: MyMonad ThreadId+-- > forkAndDo = forkIO forkedDo+-- >+-- > forkedDo :: MyMonad ()+-- > forkedDo = liftIO $ putStrLn "forkedDo running"+--+-- 'forkIO' can operate on any monad that is an instance of+-- 'ForkableMonad'. 'ForkableMonad' instances are defined for+-- 'ReaderT' and 'StateT', as well as 'IO'. Here is the precise+-- meaning of \"transplant\" for each of these:+--+--   * 'IO' requires no special work, since @Control.Concurrent@'s+--     'C.forkIO' already provides the \"transplanting\" of an 'IO'+--     action to a new thread.+--+--   * 'ReaderT' makes the parent thread's environment available for+--     consultation in the new thread.+--+--   * 'StateT' makes a /copy/ of the parent thread's state available+--     in the new thread. The states in the two threads are not+--     linked, so it is expected that they will diverge as each thread+--     updates its own copy of the state.+--+-- Other standard transformers (notably @WriterT@, @ErrorT@ and+-- @RWST@) do not have an instance defined, because those instances+-- can only be defined through data loss.+--+-- For example, the current output of a @Writer@ cannot be accessed+-- from within the monad, so the best that can be done is to create a+-- new pristine @Writer@ state for the new thread, and to discard all+-- data written in that thread when the thread terminates.+--+-- If you want to use 'forkIO' on a monad stack that includes one of+-- these lossy monads, you will need to define the 'ForkableMonad'+-- instances yourself. The same goes for any custom monads you may+-- have in the stack.+--+-- This module reexports @Control.Concurrent@ overlayed with the+-- generic 'forkIO', so you can simply change your import from+-- @Control.Concurrent@ to @Control.Concurrent.Forkable@ to use this+-- module's 'forkIO' in your existing concurrent code.+module Control.Concurrent.Forkable+       ( ForkableMonad (forkIO)+       , module Control.Concurrent+       ) where++import qualified Control.Concurrent as C+import Control.Concurrent hiding (forkIO)+import Control.Monad.Reader+import Control.Monad.State++class (MonadIO m) => ForkableMonad m where+    -- | Spark off a new thread to run the monadic computation passed+    -- as the first argument, and return the 'ThreadId' of the newly+    -- created thread.+    --+    -- The new thread will run the computation using the same monadic+    -- context as the parent thread.+    --+    -- As a convenience, this forkIO accepts a computation returning+    -- any value, not just unit. This value is discarded when the+    -- computation terminates.+    forkIO :: m a -> m C.ThreadId++instance ForkableMonad IO where+    forkIO act = C.forkIO (act >> return ())++instance (ForkableMonad m) => ForkableMonad (ReaderT r m) where+    forkIO act = do+        env <- ask+        lift $ forkIO (runReaderT act env)++instance (ForkableMonad m) => ForkableMonad (StateT s m) where+    forkIO act = do+        st <- get+        lift $ forkIO (runStateT act st)

@@ -0,0 +1,30 @@+Copyright David Anderson 2010++All rights reserved.++Redistribution and use in source and binary forms, with or without+modification, are permitted provided that the following conditions are met:++    * Redistributions of source code must retain the above copyright+      notice, this list of conditions and the following disclaimer.++    * Redistributions in binary form must reproduce the above+      copyright notice, this list of conditions and the following+      disclaimer in the documentation and/or other materials provided+      with the distribution.++    * Neither the name of David Anderson nor the names of other+      contributors may be used to endorse or promote products derived+      from this software without specific prior written permission.++THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

@@ -0,0 +1,3 @@+#!/usr/bin/env runhaskell+import Distribution.Simple+main = defaultMain

@@ -0,0 +1,57 @@+-- The name of the package.+Name:                forkable-monad++-- The package version. See the Haskell package versioning policy+-- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for+-- standards guiding when and how versions should be incremented.+Version:             0.1++-- A short (one-line) description of the package.+Synopsis:            An implementation of forkIO for monad stacks.++Description:+  This module defines a more generic version of Control.Concurrent's+  forkIO, which can directly run some complex monadic actions as well+  as plain IO actions.+++-- URL for the project homepage or repository.+Homepage:            http://code.google.com/p/forkable-monad/++-- The license under which the package is released.+License:             BSD3++-- The file containing the license text.+License-file:        LICENSE++-- The package copyright.+Copyright:           Google Inc. 2010++-- The package author(s).+Author:              David Anderson++-- An email address to which users can send suggestions, bug reports,+-- and patches.+Maintainer:          dave@natulte.net++-- Stability of the pakcage (experimental, provisional, stable...)+Stability:           Experimental++Category:            Concurrent++Build-type:          Simple++-- Constraint on the version of Cabal needed to build this package.+Cabal-version:       >=1.2++Library+  -- Modules exported by the library.+  Exposed-modules:   Control.Concurrent.Forkable++  -- Packages needed in order to build this package.+  Build-depends:     base >3.0 && <4.3,+                     mtl >=1.1 && <1.2++  -- Compiler options, for normal and profiling builds.+  Ghc-options:       -Wall+  Ghc-prof-options:  -auto-all