Control.Concurrent.NQE.Supervisor

Supervisors run and monitor processes, including other supervisors. A supervisor has a corresponding Strategy that controls its behaviour if a child stops. Supervisors deal with exceptions in concurrent processes so that their code does not need to be written in an overly-defensive style. They help prevent problems caused by processes dying quietly in the background, potentially locking an entire application.

Documentation

type ChildAction = IO ()

Alias for child action to be executed asynchronously by supervisor.

type Child = Async ()

Thread handler for child.

data SupervisorMessage

Send this message to a supervisor to add or remove a child.

type Supervisor = Process SupervisorMessage

Alias for supervisor process.

data Strategy

Supervisor strategies to decide what to do when a child stops.

Constructors

Notify (Listen (Child, Maybe SomeException))

send a SupervisorNotif to Mailbox when child dies

KillAll

kill all processes and propagate exception upstream

IgnoreGraceful

ignore processes that stop without raising an exception

IgnoreAll

keep running if a child dies and ignore it

withSupervisor :: MonadUnliftIO m => Strategy -> (Supervisor -> m a) -> m a

Run a supervisor asynchronously and pass its mailbox to a function. Supervisor will be stopped along with all its children when the function ends.

supervisor :: MonadUnliftIO m => Strategy -> m Supervisor

Run a supervisor as an asynchronous process.

supervisorProcess :: MonadUnliftIO m => Strategy -> Inbox SupervisorMessage -> m ()

Run a supervisor in the current thread.

addChild :: MonadIO m => Supervisor -> ChildAction -> m Child

Add a new ChildAction to the supervisor. Will return the Child that was just started. This function will not block or raise an exception if the child dies.

removeChild :: MonadIO m => Supervisor -> Child -> m ()

Stop a Child controlled by this supervisor. Will block until the child dies.