Maintainer	Bas van Dijk <v.dijk.bas@gmail.com> , Roel van Dijk <vandijk.roel@gmail.com>

Control.Concurrent.STM.Event

Description

An Event is a simple mechanism for communication between threads: one thread signals an event and other threads wait for it.

Each event has an internal State which is either Set or Cleared. This state can be changed with the corresponding functions set and clear. The wait function blocks until the state is Set. An important property of setting an event is that all threads waiting for it are woken.

It was inspired by the Python Event object. See:

http://docs.python.org/3.1/library/threading.html#event-objects

This module is designed to be imported qualified. We suggest importing it like:

 import           Control.Concurrent.STM.Event          ( Event )
 import qualified Control.Concurrent.STM.Event as Event ( ... )

Synopsis

Documentation

data Event Source

An event is in one of two possible states: Set or Cleared.

Instances

Eq Event
Typeable Event

data State Source

The internal state of an Event. Only interesting when you use the state function.

Constructors

Cleared
Set

Instances

Enum State
Eq State
Ord State
Read State
Show State
Typeable State

new :: STM Event Source

Create an event. The initial state is Cleared.

wait :: Event -> STM ()Source

Retry until the event is set.

If the state of the event is already Set this function will return immediately. Otherwise it will retry until another thread calls set.

You can also stop a thread that is waiting for an event by throwing an asynchronous exception.

set :: Event -> STM ()Source

Changes the state of the event to Set. All threads that where waiting for this event are woken. Threads that wait after the state is changed to Set will not retry.

clear :: Event -> STM ()Source

Changes the state of the event to Cleared. Threads that wait after the state is changed to Cleared will retry until the state is changed to Set.

state :: Event -> STM State Source

The current state of the event.