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<concept id="GUID-59BBEA98-6501-5415-A4B5-3AE8E33957D3" xml:lang="en"><title>Server

services</title><shortdesc>Describes asynchronous services provided by the client-server framework.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The majority of Symbian platform asynchronous services are provided by

servers written in accordance with the Symbian platform client-server framework.

A server is a thread running in user mode, which services requests from client

threads also running in user mode. An example of asynchronous service provided

by a server is the <codeph>EventReady(TRequestStatus* aStat)</codeph> function

provided by the <codeph>RWsSession</codeph> class — the client API to

the window server. This function requests an event from the window server,

which the user program can extract and analyse using other <codeph>RWsSession</codeph> functions.</p>

<p>As with services provided by the kernel, server-provided services are presented

to clients through a client API, typically an <codeph>R</codeph> class such

as <codeph>RWsSession</codeph>, derived from <codeph>RSessionBase</codeph>.

When the <codeph>RSessionBase</codeph> is opened, a server-side object is

created and the client’s thread id is noted. Request functions are converted

into an inter-thread message which encapsulates all the parameters. When request

functions complete, the server posts the request status and signals the client

thread’s request semaphore.</p>

<p>As with services provided by the kernel, the process of requesting asynchronous

service from a server, and handling its completion, involves messaging and

inter-thread communication. Symbian platform provides efficient services to

support these.</p>

</conbody></concept>