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# Glossary

## IO_Service

Contains the asio library's implementation of the Proactor design pattern. Acts as a registry of available services, and as a thread pool for dispatching handlers associated with completed asynchronous operations.

## Handler

A function object, typically one invoked when an asynchronous operations completes. Referred to as "Completion Handler" in the Proactor design pattern.

## Proactor

A design pattern for asynchronous event demultiplexing. A Proactor executes long running operations asynchronously, and invokes completion handlers with the result of the operation when they finish.

## Reactor

A design pattern for synchronous event demultiplexing. A Reactor associates event handlers with operating system resources (such as sockets) and notifies the event handlers when the resource is ready to perform an operation (e.g. ready to read or write without blocking). It is the responsibility of an event handler to perform the actual operation.

## Service

An object, registered with an IO_Service, responsible for implementing asynchronous operations.

| Copyright © 2003 - 2006 Christopher M. Kohlhoff