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|
{-# LANGUAGE CPP, NoImplicitPrelude, RankNTypes, ImpredicativeTypes #-}
#if __GLASGOW_HASKELL__ >= 701
{-# LANGUAGE Trustworthy #-}
#endif
--------------------------------------------------------------------------------
-- |
-- Module : Control.Concurrent.Thread
-- Copyright : (c) 2010-2012 Bas van Dijk & Roel van Dijk
-- License : BSD3 (see the file LICENSE)
-- Maintainer : Bas van Dijk <v.dijk.bas@gmail.com>
-- , Roel van Dijk <vandijk.roel@gmail.com>
--
-- Standard threads extended with the ability to /wait/ for their return value.
--
-- This module exports equivalently named functions from @Control.Concurrent@
-- (and @GHC.Conc@). Avoid ambiguities by importing this module qualified. May
-- we suggest:
--
-- @
-- import qualified Control.Concurrent.Thread as Thread ( ... )
-- @
--
-- The following is an example how to use this module:
--
-- @
--
-- import qualified Control.Concurrent.Thread as Thread ( 'forkIO', 'result' )
--
-- main = do (tid, wait) <- Thread.'forkIO' $ do x <- someExpensiveComputation
-- return x
-- doSomethingElse
-- x <- Thread.'result' =<< 'wait'
-- doSomethingWithResult x
-- @
--
--------------------------------------------------------------------------------
module Control.Concurrent.Thread
( -- * Forking threads
forkIO
, forkOS
, forkOn
, forkIOWithUnmask
, forkOnWithUnmask
-- * Results
, Result
, result
) where
--------------------------------------------------------------------------------
-- Imports
--------------------------------------------------------------------------------
-- from base:
import qualified Control.Concurrent ( forkOS
, forkIOWithUnmask
, forkOnWithUnmask
)
import Control.Concurrent ( ThreadId )
import Control.Concurrent.MVar ( newEmptyMVar, putMVar, readMVar )
import Control.Exception ( SomeException, try, throwIO, mask )
import Control.Monad ( return, (>>=) )
import Data.Either ( Either(..), either )
import Data.Function ( (.), ($) )
import Data.Int ( Int )
import System.IO ( IO )
-- from threads:
import Control.Concurrent.Raw ( rawForkIO, rawForkOn )
--------------------------------------------------------------------------------
-- * Forking threads
--------------------------------------------------------------------------------
-- | Like @Control.Concurrent.'Control.Concurrent.forkIO'@ but returns
-- a computation that when executed blocks until the thread terminates
-- then returns the final value of the thread.
forkIO :: IO a -> IO (ThreadId, IO (Result a))
forkIO = fork rawForkIO
-- | Like @Control.Concurrent.'Control.Concurrent.forkOS'@ but returns
-- a computation that when executed blocks until the thread terminates
-- then returns the final value of the thread.
forkOS :: IO a -> IO (ThreadId, IO (Result a))
forkOS = fork Control.Concurrent.forkOS
-- | Like @Control.Concurrent.'Control.Concurrent.forkOn'@ but returns
-- a computation that when executed blocks until the thread terminates
-- then returns the final value of the thread.
forkOn :: Int -> IO a -> IO (ThreadId, IO (Result a))
forkOn = fork . rawForkOn
-- | Like @Control.Concurrent.'Control.Concurrent.forkIOWithUnmask'@ but returns
-- a computation that when executed blocks until the thread terminates
-- then returns the final value of the thread.
forkIOWithUnmask
:: ((forall b. IO b -> IO b) -> IO a) -> IO (ThreadId, IO (Result a))
forkIOWithUnmask = forkWithUnmask Control.Concurrent.forkIOWithUnmask
-- | Like @Control.Concurrent.'Control.Concurrent.forkOnWithUnmask'@ but returns
-- a computation that when executed blocks until the thread terminates
-- then returns the final value of the thread.
forkOnWithUnmask
:: Int -> ((forall b. IO b -> IO b) -> IO a) -> IO (ThreadId, IO (Result a))
forkOnWithUnmask = forkWithUnmask . Control.Concurrent.forkOnWithUnmask
--------------------------------------------------------------------------------
-- Utils
--------------------------------------------------------------------------------
fork :: (IO () -> IO ThreadId) -> (IO a -> IO (ThreadId, IO (Result a)))
fork doFork = \a -> do
res <- newEmptyMVar
tid <- mask $ \restore -> doFork $ try (restore a) >>= putMVar res
return (tid, readMVar res)
forkWithUnmask
:: (((forall b. IO b -> IO b) -> IO ()) -> IO ThreadId)
-> ((forall b. IO b -> IO b) -> IO a) -> IO (ThreadId, IO (Result a))
forkWithUnmask doForkWithUnmask = \f -> do
res <- newEmptyMVar
tid <- mask $ \restore ->
doForkWithUnmask $ \unmask ->
try (restore $ f unmask) >>= putMVar res
return (tid, readMVar res)
--------------------------------------------------------------------------------
-- Results
--------------------------------------------------------------------------------
-- | A result of a thread is either some exception that was thrown in the thread
-- and wasn't catched or the actual value that was returned by the thread.
type Result a = Either SomeException a
-- | Retrieve the actual value from the result.
--
-- When the result is 'SomeException' the exception is thrown.
result :: Result a -> IO a
result = either throwIO return
|
