1 <?xml version="1.0" encoding="utf-8"?>

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    10 <!DOCTYPE concept

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    29 thread’s request semaphore.</p>

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

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

    32 inter-thread communication. Symbian platform provides efficient services to

    33 support these.</p>

    34 </conbody></concept>