Control.Concurrent.Chan.Unagi.Bounded

unagi-chan-0.4.1.4: Fast concurrent queues with a Chan-like API, and more

Safe Haskell | None
Language | Haskell2010

Control.Concurrent.Chan.Unagi.Bounded

Contents

- Creating channels
- Channel operations
  - Reading
  - Writing
  - Broadcasting

Synopsis

- newChan :: Int -> IO (InChan a, OutChan a)
- data InChan a
- data OutChan a
- readChan :: OutChan a -> IO a
- readChanOnException :: OutChan a -> (IO a -> IO ()) -> IO a
- tryReadChan :: OutChan a -> IO (Element a, IO a)
- newtype Element a = Element {
  - tryRead :: IO (Maybe a)
  }
- getChanContents :: OutChan a -> IO [a]
- estimatedLength :: InChan a -> IO Int
- writeChan :: InChan a -> a -> IO ()
- tryWriteChan :: InChan a -> a -> IO Bool
- writeList2Chan :: InChan a -> [a] -> IO ()
- dupChan :: InChan a -> IO (OutChan a)

# Documentation

A queue with bounded size, which supports a `writeChan` which blocks when the number of messages grows larger than desired. The bounds are maintained loosely between `n` and `n*2`; see the caveats and descriptions of semantics in `readChan` and `writeChan` for details.

# Creating channels

newChan :: Int -> IO (InChan a, OutChan a) #

Create a new channel of the passed size, returning its write and read ends.

The passed integer bounds will be rounded up to the next highest power of two, `n`. The queue may grow up to size `2*n` (see `writeChan` for details), and the resulting chan pair requires O(n) space.

data InChan a #

The write end of a channel created with `newChan`.

#### Instances

Instances details

Eq (InChan a) # |
Instance details Defined in Control.Concurrent.Chan.Unagi.Bounded.Internal Methods (==) :: InChan a -> InChan a -> Bool # (/=) :: InChan a -> InChan a -> Bool #

data OutChan a #

The read end of a channel created with `newChan`.

#### Instances

Instances details

Eq (OutChan a) # |
Instance details Defined in Control.Concurrent.Chan.Unagi.Bounded.Internal Methods (==) :: OutChan a -> OutChan a -> Bool # (/=) :: OutChan a -> OutChan a -> Bool #

# Channel operations

## Reading

readChan :: OutChan a -> IO a #

Read an element from the chan, blocking if the chan is empty.

Note re. exceptions: When an async exception is raised during a `readChan` the message that the read would have returned is likely to be lost, even when the read is known to be blocked on an empty queue. If you need to handle this scenario, you can use `readChanOnException`.

readChanOnException :: OutChan a -> (IO a -> IO ()) -> IO a #

Like `readChan` but allows recovery of the queue element which would have been read, in the case that an async exception is raised during the read. To be precise exceptions are raised, and the handler run, only when `readChanOnException` is blocking.

The second argument is a handler that takes a blocking IO action returning the element, and performs some recovery action. When the handler is called, the passed `IO a` is the only way to access the element.

tryReadChan :: OutChan a -> IO (Element a, IO a) #

Returns immediately with:

- an ``Element` a` future, which returns one unique element when it becomes available via `tryRead`.
- a blocking `IO` action that returns the element when it becomes available.

Note: This is a destructive operation. See `Element` for more details.

Note re. exceptions: When an async exception is raised during a `tryReadChan` the message that the read would have returned is likely to be lost, just as it would be when raised directly after this function returns.

newtype Element a #

An `IO` action that returns a particular enqueued element when and if it becomes available.

Each `Element` corresponds to a particular enqueued element, i.e. a returned `Element` always offers the only means to access one particular enqueued item. The value returned by `tryRead` moves monotonically from `Nothing` to `Just a` when and if an element becomes available, and is idempotent at that point.

So for instance:

       (in, out) <- newChan
       (el, _) <- tryReadChan out  -- READ FROM EMPTY CHAN
       writeChan in "msg1"
       writeChan in "msg2"
       readChan out        -- RETURNS "msg2"
       tryRead el          -- RETURNS "msg1" (which would otherwise be lost)

Constructors

Element |
Fields tryRead :: IO (Maybe a)

#### Instances

Instances details

Alternative Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods empty :: Element a # (<|>) :: Element a -> Element a -> Element a # some :: Element a -> Element [a] # many :: Element a -> Element [a] #
Applicative Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods pure :: a -> Element a # (<*>) :: Element (a -> b) -> Element a -> Element b # liftA2 :: (a -> b -> c) -> Element a -> Element b -> Element c # (*>) :: Element a -> Element b -> Element b # (<*) :: Element a -> Element b -> Element a #
Functor Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods fmap :: (a -> b) -> Element a -> Element b # (<$) :: a -> Element b -> Element a #
Monad Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods (>>=) :: Element a -> (a -> Element b) -> Element b # (>>) :: Element a -> Element b -> Element b # return :: a -> Element a #
MonadPlus Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods mzero :: Element a # mplus :: Element a -> Element a -> Element a #
MonadFail Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods fail :: String -> Element a #
MonadFix Element # |
Instance details Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types Methods mfix :: (a -> Element a) -> Element a #

getChanContents :: OutChan a -> IO [a] #

Return a lazy infinite list representing the contents of the supplied OutChan, much like System.IO.hGetContents.

estimatedLength :: InChan a -> IO Int #

Return the estimated length of a bounded queue

The more concurrent writes and reads that are happening, the more inaccurate the estimate of the chan's size is likely to be.

## Writing

writeChan :: InChan a -> a -> IO () #

Write a value to the channel. If the chan is full this will block.

To be precise this may block when the number of elements in the queue `>= size`, and will certainly block when `>= size*2`, where `size` is the argument passed to `newChan`, rounded up to the next highest power of two.

Note re. exceptions: In the case that an async exception is raised while blocking here, the write will nonetheless succeed. When not blocking, exceptions are masked. Thus writes always succeed once `writeChan` is entered.

tryWriteChan :: InChan a -> a -> IO Bool #

Try to write a value to the channel, aborting if the write is likely to exceed the bounds, returning a `Bool` indicating whether the write was successful.

This function never blocks, but may occasionally write successfully to a queue that is already "full". Unlike `writeChan` this function treats the requested bounds (raised to nearest power of two) strictly, rather than using the `n .. n*2` range. The more concurrent writes and reads that are happening, the more inaccurate the estimate of the chan's size is likely to be.

writeList2Chan :: InChan a -> [a] -> IO () #

Write an entire list of items to a chan type. Writes here from multiple threads may be interleaved, and infinite lists are supported.

## Broadcasting

dupChan :: InChan a -> IO (OutChan a) #

Duplicate a chan: the returned `OutChan` begins empty, but data written to the argument `InChan` from then on will be available from both the original `OutChan` and the one returned here, creating a kind of broadcast channel.

Writers will be blocked only when the fastest reader falls behind the bounds; slower readers of duplicated `OutChan` may fall arbitrarily behind.