|Basic concurrency stuff.|
|Forking and suchlike|
|forkIO :: IO () -> IO ThreadId|
The new thread will be a lightweight thread; if you want to use a foreign library that uses thread-local storage, use Control.Concurrent.forkOS instead.
GHC note: the new thread inherits the blocked state of the parent (see Control.Exception.block).
The newly created thread has an exception handler that discards the exceptions BlockedOnDeadMVar, BlockedIndefinitely, and ThreadKilled, and passes all other exceptions to the uncaught exception handler (see setUncaughtExceptionHandler).
|forkOnIO :: Int -> IO () -> IO ThreadId|
Like forkIO, but lets you specify on which CPU the thread is created. Unlike a forkIO thread, a thread created by forkOnIO will stay on the same CPU for its entire lifetime (forkIO threads can migrate between CPUs according to the scheduling policy). forkOnIO is useful for overriding the scheduling policy when you know in advance how best to distribute the threads.
The Int argument specifies the CPU number; it is interpreted modulo numCapabilities (note that it actually specifies a capability number rather than a CPU number, but to a first approximation the two are equivalent).
|numCapabilities :: Int|
|the value passed to the +RTS -N flag. This is the number of Haskell threads that can run truly simultaneously at any given time, and is typically set to the number of physical CPU cores on the machine.|
|childHandler :: SomeException -> IO ()|
|myThreadId :: IO ThreadId|
|Returns the ThreadId of the calling thread (GHC only).|
|killThread :: ThreadId -> IO ()|
killThread terminates the given thread (GHC only). Any work already done by the thread isn't lost: the computation is suspended until required by another thread. The memory used by the thread will be garbage collected if it isn't referenced from anywhere. The killThread function is defined in terms of throwTo:
killThread tid = throwTo tid ThreadKilled
Killthread is a no-op if the target thread has already completed.
|throwTo :: Exception e => ThreadId -> e -> IO ()|
throwTo raises an arbitrary exception in the target thread (GHC only).
throwTo does not return until the exception has been raised in the target thread. The calling thread can thus be certain that the target thread has received the exception. This is a useful property to know when dealing with race conditions: eg. if there are two threads that can kill each other, it is guaranteed that only one of the threads will get to kill the other.
If the target thread is currently making a foreign call, then the exception will not be raised (and hence throwTo will not return) until the call has completed. This is the case regardless of whether the call is inside a block or not.
Important note: the behaviour of throwTo differs from that described in the paper "Asynchronous exceptions in Haskell" (http://research.microsoft.com/~simonpj/Papers/asynch-exns.htm). In the paper, throwTo is non-blocking; but the library implementation adopts a more synchronous design in which throwTo does not return until the exception is received by the target thread. The trade-off is discussed in Section 8 of the paper. Like any blocking operation, throwTo is therefore interruptible (see Section 4.3 of the paper).
There is currently no guarantee that the exception delivered by throwTo will be delivered at the first possible opportunity. In particular, if a thread may unblock and then re-block exceptions (using unblock and block) without receiving a pending throwTo. This is arguably undesirable behaviour.
|par :: a -> b -> b|
|pseq :: a -> b -> b|
|yield :: IO ()|
|The yield action allows (forces, in a co-operative multitasking implementation) a context-switch to any other currently runnable threads (if any), and is occasionally useful when implementing concurrency abstractions.|
|labelThread :: ThreadId -> String -> IO ()|
labelThread stores a string as identifier for this thread if you built a RTS with debugging support. This identifier will be used in the debugging output to make distinction of different threads easier (otherwise you only have the thread state object's address in the heap).
|threadStatus :: ThreadId -> IO ThreadStatus|
|threadDelay :: Int -> IO ()|
Suspends the current thread for a given number of microseconds (GHC only).
There is no guarantee that the thread will be rescheduled promptly when the delay has expired, but the thread will never continue to run earlier than specified.
|registerDelay :: Int -> IO (TVar Bool)|
|Set the value of returned TVar to True after a given number of microseconds. The caveats associated with threadDelay also apply.|
|threadWaitRead :: Fd -> IO ()|
|Block the current thread until data is available to read on the given file descriptor (GHC only).|
|threadWaitWrite :: Fd -> IO ()|
|Block the current thread until data can be written to the given file descriptor (GHC only).|
|data MVar a|
|newMVar :: a -> IO (MVar a)|
|Create an MVar which contains the supplied value.|
|newEmptyMVar :: IO (MVar a)|
|Create an MVar which is initially empty.|
|takeMVar :: MVar a -> IO a|
There are two further important properties of takeMVar:
|putMVar :: MVar a -> a -> IO ()|
There are two further important properties of putMVar:
|tryTakeMVar :: MVar a -> IO (Maybe a)|
|A non-blocking version of takeMVar. The tryTakeMVar function returns immediately, with Nothing if the MVar was empty, or Just a if the MVar was full with contents a. After tryTakeMVar, the MVar is left empty.|
|tryPutMVar :: MVar a -> a -> IO Bool|
|A non-blocking version of putMVar. The tryPutMVar function attempts to put the value a into the MVar, returning True if it was successful, or False otherwise.|
|isEmptyMVar :: MVar a -> IO Bool|
Check whether a given MVar is empty.
Notice that the boolean value returned is just a snapshot of the state of the MVar. By the time you get to react on its result, the MVar may have been filled (or emptied) - so be extremely careful when using this operation. Use tryTakeMVar instead if possible.
|addMVarFinalizer :: MVar a -> IO () -> IO ()|
|Add a finalizer to an MVar (GHC only). See Foreign.ForeignPtr and System.Mem.Weak for more about finalizers.|
|newtype STM a|
|atomically :: STM a -> IO a|
Perform a series of STM actions atomically.
You cannot use atomically inside an unsafePerformIO or unsafeInterleaveIO. Any attempt to do so will result in a runtime error. (Reason: allowing this would effectively allow a transaction inside a transaction, depending on exactly when the thunk is evaluated.)
|retry :: STM a|
|Retry execution of the current memory transaction because it has seen values in TVars which mean that it should not continue (e.g. the TVars represent a shared buffer that is now empty). The implementation may block the thread until one of the TVars that it has read from has been udpated. (GHC only)|
|orElse :: STM a -> STM a -> STM a|
|Compose two alternative STM actions (GHC only). If the first action completes without retrying then it forms the result of the orElse. Otherwise, if the first action retries, then the second action is tried in its place. If both actions retry then the orElse as a whole retries.|
|catchSTM :: STM a -> (SomeException -> STM a) -> STM a|
|Exception handling within STM actions.|
|alwaysSucceeds :: STM a -> STM ()|
|alwaysSucceeds adds a new invariant that must be true when passed to alwaysSucceeds, at the end of the current transaction, and at the end of every subsequent transaction. If it fails at any of those points then the transaction violating it is aborted and the exception raised by the invariant is propagated.|
|always :: STM Bool -> STM ()|
|always is a variant of alwaysSucceeds in which the invariant is expressed as an STM Bool action that must return True. Returning False or raising an exception are both treated as invariant failures.|
|data TVar a|
|newTVar :: a -> STM (TVar a)|
|Create a new TVar holding a value supplied|
|newTVarIO :: a -> IO (TVar a)|
|IO version of newTVar. This is useful for creating top-level TVars using System.IO.Unsafe.unsafePerformIO, because using atomically inside System.IO.Unsafe.unsafePerformIO isn't possible.|
|readTVar :: TVar a -> STM a|
|Return the current value stored in a TVar|
|writeTVar :: TVar a -> a -> STM ()|
|Write the supplied value into a TVar|
|unsafeIOToSTM :: IO a -> STM a|
Unsafely performs IO in the STM monad. Beware: this is a highly dangerous thing to do.
|signalHandlerLock :: MVar ()|
|ensureIOManagerIsRunning :: IO ()|
|setUncaughtExceptionHandler :: (SomeException -> IO ()) -> IO ()|
|getUncaughtExceptionHandler :: IO (SomeException -> IO ())|
|reportError :: SomeException -> IO a|
|reportStackOverflow :: IO a|
|Produced by Haddock version 2.3.0|