Control.Concurrent.Bag.Safe

High level bag of tasks interface needing no explicit control. Tasks can only return results and add new tasks as intended and it is not possible to add new tasks from the outside or from the action processing the results. This way it is possible to ensure that getResults returns only Nothing if it is safe to say that there will be no results anymore.

Documentation

data BagT r m a

A monad transformer for processing the results of the bag sequencially. In addition to the actions available in the base monad, which has to be an instance of MonadIO in all functions, it provides the action getResult to get a result of the bag.

Instances

MonadTrans (BagT r)

Monad m => Monad (BagT r m)

Monad m => Functor (BagT r m)

Monad m => Applicative (BagT r m)

MonadIO m => MonadIO (BagT r m)

newTaskBag

Arguments

:: MonadIO m

=> BufferType

-> Maybe (SplitFunction r)

Possible split function If the function is given, we will create a bag with one buffer per worker reducing the communication between the workers.

-> [TaskIO r (Maybe r)]

list of initial tasks

-> BagT r m a

action to process the results of the bag

-> m a

Initializes a new bag of tasks and starts a gang of workers threads. The number of worker threads is equal to the number of capabilities of the Haskell runtime (see getNumCapabilities).

__WARNING__: If it may be necessary to terminate the thread pool, i.e. because the result processing function does not always request all values, you have to make sure that the task can be stopped. Terminating the tasks is done with asynchronous exceptions which can only be received at a emph{safe point}. Safe points are all points where memory allocation is requested, but there are calculations and also loops which never need any new memory. These calculations cannot be terminated and may run forever, see the documentation of throwTo.

newEvalBag :: MonadIO m => BufferType -> Maybe (SplitFunction r) -> [r] -> BagT r m a -> m a

Like newTaskBag, but it takes a list of expressions that will be evaluated to weak head normal form using seq.

__WARNING__: This does not evaluate to normal form, but only to weak head normal form.

newInterruptibleBag :: MonadIO m => BufferType -> Maybe (SplitFunction r) -> [Interruptible r] -> BagT r m a -> m a

newInterruptingBag :: MonadIO m => BufferType -> Maybe (SplitFunction r) -> [Interruptible r] -> BagT r m a -> m a

Similar to newTaskBag, but interrupts the tasks in certain intervals. Using a TChan as buffer, this ensures completeness: all tasks that have a result will get their time to evaluate it. Note, that calculations, that do no memory allocation, cannot be interrupted.

getResult :: MonadIO m => BagT r m (Maybe r)

Get a result of the bag if there is one. If it returns Nothing, all tasks have been processed and there are no results left. getResults blocks until a task has been evaluated to a result or all tasks are processed. Therefore it may block forever.

getAllResults :: MonadIO m => BagT a m [a]

Convenience function to get all results from the bag of tasks.

liftIO :: MonadIO m => forall a. IO a -> m a

Lift a computation from the IO monad.

lift :: MonadTrans t => forall m a. Monad m => m a -> t m a

Lift a computation from the argument monad to the constructed monad.

data TaskBufferSTM a

Constructors

TaskBufferSTM

Fields

writeBufferSTM :: a -> STM ()

unGetBufferSTM :: a -> STM ()

readBufferSTM :: STM a

tryReadBufferSTM :: STM (Maybe a)

isEmptyBufferSTM :: STM Bool

type SplitFunction r = TaskBufferSTM (IO (Maybe r)) -> TaskBufferSTM (IO (Maybe r)) -> STM (IO (Maybe r))

takeFirst :: SplitFunction r

module Control.Concurrent.Bag.Task

data BufferType

Constructors

Queue

Stack