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Structure

The Reactor pattern (shown in Figure 1) involves the following objects:

Figure 1: Structure of Reactor pattern

Handles

Handles are objects by which incoming communication channels or similar entities (e.g. timers, files, synchronisation constructs) are accessed and events received from them.

Synchronous event demultiplexer (demux)

A demux is given a set of handles and has a method called select that waits until an event is received. When select is called, the demux waits until at least one handle has an unread event and then reports that a message can be read.

Event handler

An event handler has a single method handleEvent that takes an event as a parameter and processes it in whatever manner the application needs.

Initiation dispatcher

A dispatcher has a set of handle/event handler pairs and methods to add and remove such pairs. It has a method handleEvents that repeatedly uses a demux to wait for events on the handles in the set and then sends each event to the corresponding event handler.

A typical Reactor-based application uses only one dispatcher and therefore only one demux and one thread (although the Reactor implementation may contain additional threads).

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Next: Example Up: Reactor Previous: Introduction