Apadmi Symbian Essentials Using Servers Donation Presentation

8/14/2019 Apadmi Symbian Essentials Using Servers Donation Presentation

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Apadmi Symbian Essentials

Using Servers


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Copyright Apadmi Ltd 2009.

Objectives

Illustrate importance of client-serverarchitectureLook at some key system serversPlug-in architectures

Find out how to use a serverClient-side APISessions & subsessionsWorking with asynchronous APIs

Handles and the Cleanup Stack


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System Servers


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Plug-in Architecture

SocketsServer

InfraredProtocols TCP/IP

File ServerLocal FileSystem Flash FilingSystem

SMS


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Client-Server Overview

Session-basedmultiple sessionssubsessions

Client service API Inter-thread communication Safe

isolation in separate processmessage passing between client & server


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Using a simple server

RCountServSession session;TRequestStatus status;

User::LeaveIfError(session.Connect());

_LIT(KTxtLegalString,"224");

ret = session.SetFromString(KTxtLegalString);

session.DelayedIncrease(1, 1000000, status);User::WaitForRequest(status);

session.DecreaseBy(3);

session.Close();


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Sessions

Server thread.

Client thread

with two sessions

Multiple sessions

Example system with 1 server and 1client thread

2 client sessions exist within a singlethread


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Subsessions

Better (more lightweight) way for asingle client to have multiple logical

connections with one server

Server side

Client side


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Client-side classes (1)

Two classes are used to produce clientside APIs

RSessionBaseRSubSessionBase

Derived classes must:Create sessions or subsessions as

appropriate

Send request messages from the client tothe server


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Client-side classes (2)

Create a session withRSessionBase::CreateSession()

Create a subsession withRSubSessionBase::CreateSubSession()

Send messages withSend(TInt aFunction,TAny* aPtr)SendReceive(TInt aFunction,TAny*aPtr,TRequestStatus& aStatus)

SendReceive(TInt aFunction,TAny*aPtr)


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Client-side DLL

Client Side API often built as DLL Access services using export library

File Server: efsrv.libSocket Server: esock.libetc.

KernelExec

EUSER

Client

Server

SrvrClient

DLL


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Messages (1)

Clients send messages to servers Each message is a request for a service

Server processes requestPerforms work on behalf of client(Optionally) sends a reply to the client

Two types of message:synchronousasynchronous


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Messages (2)

Request messages simply consist offive 32-bit numbersA function number (or opcode)Four 32-bit parameters

Each of the 32-bit parameters can be:An integer, orA pointer to a flat data structure, wrapped

as a descriptor


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A real API...

class RFs : public RSessionBase {}class RFsBase : public RSubSessionBase {}

class RFile : public RFsBase{public:

IMPORT_C TInt Open(RFs& aFs, const TDesC&

aName, TUint aFileMode);IMPORT_C TInt Read(TDes8& aDes) const;IMPORT_C void Read(TDes8& aDes,

TRequestStatus& aStatus) const;IMPORT_C TInt Write(const TDesC8& aDes);IMPORT_C void Write(const TDesC8& aDes,

TRequestStatus& aStatus);

};


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Implementation Issues

Beyond the client service API

A server publishes a client service API This API should be sufficient to enable

a client to utilise the server effectively

using an R-class session/subsession But a higher-level API is often desirable

hide implementation details such asopcodes and package buffers


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Handling an asynchronous method

Write an active object, which has anRFile as its service provider

Handle completion of asynchronousrequests in the active objects RunL()method

void RFile::Read(TDes8& aDes,TRequestStatus& aStatus) const;


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Implementation Issues

Handles & the cleanup stack

All client-side APIs are derived fromRSessionBaseRSessionBase is derived fromRHandleBase

Every client-side API is a handle on aserver side session

You must look after any handles

Just as you would with pointers


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Example: handles & the cleanup stack

The file server session (fs) is protectedagainst leaves during the Connect()and Delete() calls by storing it on thecleanup stack

void CClass::SomeFunctionL(){RFs fs;CleanupClosePushL(fs);User::LeaveIfError(fs.Connect());User::LeaveIfError(fs.Delete(KSomeFileName));CleanupStack::PopAndDestroy();// fs

}


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Summary

Large number of system serversFundamental Symbian OS architecture Plug-in architecture can provide server

with extensibility and future-proofing

Sessions and subsessions Synchronous and asynchronous APIs Higher-level APIs Using the cleanup stack with handles

(R-classes)


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End of Using Servers Section

Next section is File Server and StreamStores


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About Apadmi

Apadmi is an international mobile consultancy, training anddevelopment company with an excellent reputation for providing

top quality engineering and training services to the Symbian

community.

Our training is undertaken by our Senior Technical Consultants,who have over 10 years of experience running Symbian OS

training sessions, boot camps and technical workshopsthroughout the world for companies such as Nokia, Symbian,

Sony Ericsson, Motorola, Siemens, UIQ and Orange.

For more information please go to :

http://www.apadmi.com/training.html

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Apadmi Symbian Essentials Using Servers Donation Presentation