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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<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>