Control.Immortal

This module is designed to be imported qualified, e.g.

import qualified Control.Immortal as Immortal

Documentation

data Thread

Immortal thread identifier (including its underlying ThreadId)

create :: MonadBaseControl IO m => m () -> m Thread

Spawn a new immortal thread running the given computation.

If the computation ever finishes (either normally or due to an exception), it will be restarted (in the same thread).

The monadic «state» (captured by thMonadBaseControl instance) will be preserved if the computation terminates normally, and reset when the exception is thrown, so be cautious when m is stateful. It is completely safe, however, to instantiate m with something like ReaderT conf IO to pass configuration to the new thread.

createWithLabel :: MonadBaseControl IO m => String -> m () -> m Thread

Like create, but also apply the given label to the thread (using labelThread).

stop :: Thread -> IO ()

Stop (kill) an immortal thread.

This is the only way to really stop an immortal thread.

threadId :: Thread -> ThreadId

Get the ThreadId of the immortal thread.

The ThreadId can be used to throw asynchronous exception to interrupt the computation. This won't kill the thread, however — even if the exception is not handled, the computation will be simply restarted.

onFinish :: MonadBaseControl IO m => (Either SomeException () -> m ()) -> m () -> m ()

Run a callback every time the action finishes. This can be used e.g. to log exceptions or attempts to exit when such attempts are not expected. Example usage:

Immortal.create $ Immortal.onFinish print myAction

This is nothing more than a simple wrapper around try.