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<concept id="GUID-2B8D3611-5B97-50E7-A9DD-23626A8EFB45" xml:lang="en"><title>Introduction

to active objects and the active scheduler</title><shortdesc>This document provides a short introduction to active objects and

active schedulers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-A139EAE2-5471-496C-B584-DE10D7415CD3"><title>Active objects</title> <p>An active object is a convenient

encapsulation of the behaviour involved in making requests to an asynchronous

service provider and handling the completion of those requests. Specifically,

it encapsulates the service provider's request, cancel functions and the function

which handles the completion of those requests. </p> <p>Some asynchronous

service providers supply active object based classes as interfaces through

which clients access them. </p> <p>An active object is an instance of a <codeph>CActive</codeph> derived

class. </p> </section>

<section id="GUID-73A2BF4F-AE0A-4357-AE75-EA5AA678109F"><title>The active scheduler</title> <p>An active scheduler encapsulates

the wait loop which is at the heart of all programs using multiple asynchronous

services. </p> <p>An active scheduler is an instance of a <codeph>CActiveScheduler</codeph> class

or, in some circumstances, an instance of a <codeph>CActiveScheduler</codeph> <i>derived</i> class. </p> <p>Active

objects, together with the active scheduler, provide a system of non pre-emptive

multi-tasking which runs on a single thread. </p> <p>In Symbian platform,

it is easier to write a system of co-operating active objects than a system

of co-operating threads. The run-time cost of an active object is significantly

less than that of a thread. Creating and destroying active objects is more

efficient than creating and destroying threads. </p> <p><b>See

also</b> </p> <p> <xref href="GUID-C0C19F93-D804-5AED-90E4-A814FA6A3732.dita">Low

Level Asynchronous Service Handling</xref> </p> </section>