+{-# LANGUAGE CPP
+ , ForeignFunctionInterface
+ , MagicHash
+ , UnboxedTuples
+ , ScopedTypeVariables
+ #-}
+{-# OPTIONS_GHC -fno-warn-unused-imports #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : Control.Concurrent
forkIO,
#ifdef __GLASGOW_HASKELL__
+ forkIOWithUnmask,
killThread,
throwTo,
#endif
+ -- ** Threads with affinity
+ forkOn,
+ forkOnWithUnmask,
+ getNumCapabilities,
+ threadCapability,
+
-- * Scheduling
-- $conc_scheduling
forkOS,
isCurrentThreadBound,
runInBoundThread,
- runInUnboundThread
+ runInUnboundThread,
#endif
-- * GHC's implementation of concurrency
-- ** Pre-emption
-- $preemption
+
+ -- * Deprecated functions
+ forkIOUnmasked
+
) where
import Prelude
-import Control.Exception as Exception
+import Control.Exception.Base as Exception
#ifdef __GLASGOW_HASKELL__
-import GHC.Conc ( ThreadId(..), myThreadId, killThread, yield,
- threadDelay, forkIO, childHandler )
+import GHC.Exception
+import GHC.Conc hiding (threadWaitRead, threadWaitWrite)
import qualified GHC.Conc
-import GHC.TopHandler ( reportStackOverflow, reportError )
-import GHC.IOBase ( IO(..) )
-import GHC.IOBase ( unsafeInterleaveIO )
-import GHC.IOBase ( newIORef, readIORef, writeIORef )
+import GHC.IO ( IO(..), unsafeInterleaveIO, unsafeUnmask )
+import GHC.IORef ( newIORef, readIORef, writeIORef )
import GHC.Base
import System.Posix.Types ( Fd )
#ifdef mingw32_HOST_OS
import Foreign.C
import System.IO
-import GHC.Handle
#endif
#endif
libraries (OpenGL, for example) will not work from a thread created using
'forkIO'. They work fine in threads created using 'forkOS' or when called
from @main@ or from a @foreign export@.
+
+In terms of performance, 'forkOS' (aka bound) threads are much more
+expensive than 'forkIO' (aka unbound) threads, because a 'forkOS'
+thread is tied to a particular OS thread, whereas a 'forkIO' thread
+can be run by any OS thread. Context-switching between a 'forkOS'
+thread and a 'forkIO' thread is many times more expensive than between
+two 'forkIO' threads.
+
+Note in particular that the main program thread (the thread running
+@Main.main@) is always a bound thread, so for good concurrency
+performance you should ensure that the main thread is not doing
+repeated communication with other threads in the system. Typically
+this means forking subthreads to do the work using 'forkIO', and
+waiting for the results in the main thread.
+
-}
-- | 'True' if bound threads are supported.
foreign import ccall rtsSupportsBoundThreads :: Bool
-{- |
-Like 'forkIO', this sparks off a new thread to run the 'IO' computation passed as the
-first argument, and returns the 'ThreadId' of the newly created
-thread.
-
-However, @forkOS@ uses operating system-supplied multithreading support to create
-a new operating system thread. The new thread is /bound/, which means that
-all foreign calls made by the 'IO' computation are guaranteed to be executed
-in this new operating system thread; also, the operating system thread is not
-used for any other foreign calls.
-
-This means that you can use all kinds of foreign libraries from this thread
-(even those that rely on thread-local state), without the limitations of 'forkIO'.
-
-Just to clarify, 'forkOS' is /only/ necessary if you need to associate
-a Haskell thread with a particular OS thread. It is not necessary if
-you only need to make non-blocking foreign calls (see
-"Control.Concurrent#osthreads"). Neither is it necessary if you want
-to run threads in parallel on a multiprocessor: threads created with
-'forkIO' will be shared out amongst the running CPUs (using GHC,
-@-threaded@, and the @+RTS -N@ runtime option).
-
+{- |
+Like 'forkIO', this sparks off a new thread to run the 'IO'
+computation passed as the first argument, and returns the 'ThreadId'
+of the newly created thread.
+
+However, 'forkOS' creates a /bound/ thread, which is necessary if you
+need to call foreign (non-Haskell) libraries that make use of
+thread-local state, such as OpenGL (see "Control.Concurrent#boundthreads").
+
+Using 'forkOS' instead of 'forkIO' makes no difference at all to the
+scheduling behaviour of the Haskell runtime system. It is a common
+misconception that you need to use 'forkOS' instead of 'forkIO' to
+avoid blocking all the Haskell threads when making a foreign call;
+this isn't the case. To allow foreign calls to be made without
+blocking all the Haskell threads (with GHC), it is only necessary to
+use the @-threaded@ option when linking your program, and to make sure
+the foreign import is not marked @unsafe@.
-}
+
forkOS :: IO () -> IO ThreadId
foreign export ccall forkOS_entry
foreign import ccall "forkOS_entry" forkOS_entry_reimported
:: StablePtr (IO ()) -> IO ()
+forkOS_entry :: StablePtr (IO ()) -> IO ()
forkOS_entry stableAction = do
action <- deRefStablePtr stableAction
action
foreign import ccall forkOS_createThread
:: StablePtr (IO ()) -> IO CInt
+failNonThreaded :: IO a
failNonThreaded = fail $ "RTS doesn't support multiple OS threads "
++"(use ghc -threaded when linking)"
-forkOS action
+forkOS action0
| rtsSupportsBoundThreads = do
mv <- newEmptyMVar
- let action_plus = Exception.catch action childHandler
+ b <- Exception.getMaskingState
+ let
+ -- async exceptions are masked in the child if they are masked
+ -- in the parent, as for forkIO (see #1048). forkOS_createThread
+ -- creates a thread with exceptions masked by default.
+ action1 = case b of
+ Unmasked -> unsafeUnmask action0
+ MaskedInterruptible -> action0
+ MaskedUninterruptible -> uninterruptibleMask_ action0
+
+ action_plus = Exception.catch action1 childHandler
+
entry <- newStablePtr (myThreadId >>= putMVar mv >> action_plus)
err <- forkOS_createThread entry
when (err /= 0) $ fail "Cannot create OS thread."
else do
ref <- newIORef undefined
let action_plus = Exception.try action >>= writeIORef ref
- resultOrException <-
- bracket (newStablePtr action_plus)
- freeStablePtr
- (\cEntry -> forkOS_entry_reimported cEntry >> readIORef ref)
- case resultOrException of
- Left exception -> Exception.throw exception
- Right result -> return result
+ bracket (newStablePtr action_plus)
+ freeStablePtr
+ (\cEntry -> forkOS_entry_reimported cEntry >> readIORef ref) >>=
+ unsafeResult
| otherwise = failNonThreaded
{- |
doesn't need it's main thread to be bound and makes /heavy/ use of concurrency
(e.g. a web server), might want to wrap it's @main@ action in
@runInUnboundThread@.
+
+Note that exceptions which are thrown to the current thread are thrown in turn
+to the thread that is executing the given computation. This ensures there's
+always a way of killing the forked thread.
-}
runInUnboundThread :: IO a -> IO a
runInUnboundThread action = do
- bound <- isCurrentThreadBound
- if bound
- then do
- mv <- newEmptyMVar
- forkIO (Exception.try action >>= putMVar mv)
- takeMVar mv >>= \either -> case either of
- Left exception -> Exception.throw exception
- Right result -> return result
- else action
-
+ bound <- isCurrentThreadBound
+ if bound
+ then do
+ mv <- newEmptyMVar
+ mask $ \restore -> do
+ tid <- forkIO $ Exception.try (restore action) >>= putMVar mv
+ let wait = takeMVar mv `Exception.catch` \(e :: SomeException) ->
+ Exception.throwTo tid e >> wait
+ wait >>= unsafeResult
+ else action
+
+unsafeResult :: Either SomeException a -> IO a
+unsafeResult = either Exception.throwIO return
#endif /* __GLASGOW_HASKELL__ */
+#ifdef __GLASGOW_HASKELL__
-- ---------------------------------------------------------------------------
-- threadWaitRead/threadWaitWrite
-- | Block the current thread until data is available to read on the
-- given file descriptor (GHC only).
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread was blocked. To safely close a file descriptor
+-- that has been used with 'threadWaitRead', use
+-- 'GHC.Conc.closeFdWith'.
threadWaitRead :: Fd -> IO ()
threadWaitRead fd
#ifdef mingw32_HOST_OS
-- and this only works with -threaded.
| threaded = withThread (waitFd fd 0)
| otherwise = case fd of
- 0 -> do hWaitForInput stdin (-1); return ()
+ 0 -> do _ <- hWaitForInput stdin (-1)
+ return ()
-- hWaitForInput does work properly, but we can only
-- do this for stdin since we know its FD.
_ -> error "threadWaitRead requires -threaded on Windows, or use System.IO.hWaitForInput"
-- | Block the current thread until data can be written to the
-- given file descriptor (GHC only).
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread was blocked. To safely close a file descriptor
+-- that has been used with 'threadWaitWrite', use
+-- 'GHC.Conc.closeFdWith'.
threadWaitWrite :: Fd -> IO ()
threadWaitWrite fd
#ifdef mingw32_HOST_OS
withThread :: IO a -> IO a
withThread io = do
m <- newEmptyMVar
- forkIO $ try io >>= putMVar m
+ _ <- mask_ $ forkIO $ try io >>= putMVar m
x <- takeMVar m
case x of
Right a -> return a
- Left e -> throwIO e
+ Left e -> throwIO (e :: IOException)
waitFd :: Fd -> CInt -> IO ()
waitFd fd write = do
- throwErrnoIfMinus1 "fdReady" $
- fdReady (fromIntegral fd) write (fromIntegral iNFINITE) 0
- return ()
+ throwErrnoIfMinus1_ "fdReady" $
+ fdReady (fromIntegral fd) write iNFINITE 0
-iNFINITE = 0xFFFFFFFF :: CInt -- urgh
+iNFINITE :: CInt
+iNFINITE = 0xFFFFFFFF -- urgh
foreign import ccall safe "fdReady"
fdReady :: CInt -> CInt -> CInt -> CInt -> IO CInt
The "System.IO" library manages multiplexing in its own way. On
Windows systems it uses @safe@ foreign calls to ensure that
threads doing I\/O operations don't block the whole runtime,
- whereas on Unix systems all the currently blocked I\/O reqwests
+ whereas on Unix systems all the currently blocked I\/O requests
are managed by a single thread (the /IO manager thread/) using
@select@.
lock is woken up, but haven't found it to be useful for anything
other than this example :-)
-}
+#endif /* __GLASGOW_HASKELL__ */
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