Control.Concurrent.PostMessAge

Mechanism to get messages sent to a handle concurrently without getting them mixed. They are sent to the handle in the same order they are received by a passer object (see Passer), not sending a message before the previous message is sent completely.

Passer type

data Passer handle msg

The Passer is the object that you send the messages to. It will redirect this message to its attached handle, making sure the messages are not intercalated. Use postMessage to send message to a passer object.

Open/Close a passer

createPasser

Arguments

:: handle

Handle to use

-> (handle -> msg -> IO ())

Function to send messages to the handle

-> IO (Passer handle msg)

Create a passer object from a handle and a function to send values to that handle.

Example:

createPasser stderr hPutStrLn

closePasser :: Passer handle msg -> IO ()

Close a passer object, so it won't receive any more messages in the future. Once a passer object is closed, it can't be re-opened again. If you want to reuse a handle, create another passer object with createPasser.

Send messages to the passer

postMessage :: Passer handle msg -> msg -> IO Bool

Send a message to a passer object. It returns a value indicating if the message reached the passer object.

Check passer status

isPasserClosed :: Passer handle msg -> IO Bool

Check if a passer object is closed. When a passer object is closed, it won't send any more messages to its attached handle. This does not mean the handle itself is closed.

isPasserOpen :: Passer handle msg -> IO Bool

Check if a passer object is open. While a passer object is open, all the messages received by the passer are sent to its attached handle.

Handle

passerHandle :: Passer handle msg -> handle

Return the handle used by a passer object.