Server Classes in Java

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125 Server Classes
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The fundamental server-side classes, deriving from CServer and CSharableSession, are de ned as follows:
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class CHerculeanServer : public CServer // Receives client requests { public: static CServer* NewLC(); void AddSession(); void RemoveSession();
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protected: virtual TInt RunError(TInt aError); // Overrides CActive::RunError() private: CHerculeanServer(); void ConstructL(); virtual CSharableSession* NewSessionL(const TVersion& aVersion) const; // From CServer private: TInt iSessionCount; CShutdown iShutdown; }; inline CHerculeanServer::CHerculeanServer() :CServer(0, ESharableSessions){} class CAsyncHandler; // Active object class for asynchronous requests // Services client requests class CHerculeanSession : public CSharableSession { public: CHerculeanSession(){}; virtual void CreateL(const CServer& aServer); private: void SlayNemeanLionL(const RMessage& aMessage); void SlayHydraL(const RMessage& aMessage); void CaptureCeryneianHindL(const RMessage& aMessage); void SlayErymanthianBoarL(const RMessage& aMessage); void CleanAugeanStablesL(const RMessage& aMessage); void SlayStymphalianBirdsL(const RMessage& aMessage); private: CHerculeanSession(); inline CHerculeanServer& Server(); void ServiceL(const RMessage& aMessage); // From CSharableSession private: CAsyncHandler* iAsyncRequestHandler; HBufC8* iClientBuf; }; inline CHerculeanServer& CHerculeanSession::Server() { return *static_cast<CHerculeanServer*>(const_cast<CServer*> (CSharableSession::Server())); }
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The CServer-derived class CHerculeanServer is the main server class; it coordinates server startup and shutdown and, as I described in the previous chapter, receives incoming requests The system creates a single instance of CHerculeanServer on server startup The CServer base class manages a doubly-linked list of connected client sessions When the server class receives a client request, it passes it to the associated CHerculeanSession object for handling Let s examine the code for the CHerculeanServer class in more detail (I ve omitted some of the straightforward construction code to keep the code sample as short as possible):
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SERVER CLASSES
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// Starts the server and constructs the shutdown object, starting the // timer to ensure that the server will exit even if the starting client // connection fails void CHerculeanServer::ConstructL() { StartL(KServerName); iShutdownConstructL(); iShutdownStart(); // In case the client session fails to connect } void CHerculeanServer::AddSession() { ++iSessionCount; iShutdownCancel();// Cancel the shutdown timer now } // Decrement the session counter Start the shutdown timer when the last // client disconnects void CHerculeanServer::RemoveSession() { if (--iSessionCount==0) iShutdownStart(); } TInt CHerculeanServer::RunError(TInt aError) { if (KErrBadDescriptor==aError) PanicClient(Message(),EPanicBadDescriptor); else Message()Complete(aError); ReStart(); // Continue reading client requests return (KErrNone); // handled the error }
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The construction of the CHerculeanServer class is straightforward The shutdown timer is started when the server is rst constructed, in case construction of the initial client session fails When the rst session is added successfully, the session count is incremented and the shutdown timer is canceled The server object increments and decrements the iSessionCount reference count accordingly when sessions are added and removed CHerculeanServer::RunError() is called if a leave occurs in CHerculeanSession::ServiceL(), that is, if one of the methods which services client requests leaves The leave code is passed to RunError(), which should attempt to handle the leave, returning KErrNone if it does so CServer::RunError() was added to Symbian OS v60 to allow the server to manage leaves resulting from client request processing Previously, the leaves were propagated to the active scheduler which did not have suf cient context in which to handle them RunError() panics the client if the leave code is KErrBadDescriptor, because this indicates that client data has been passed to the server without having been properly descriptorized This is
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indicative of a programming error, so the server is justi ed in panicking the client Under all other circumstances, the server reports the error to the client by completing it using RMessage::Complete() It is rarely correct to panic another thread except to indicate a programming error The code used by CHerculeanServer to panic the client is shown below RMessage::Panic() uses the RThread handle it holds for the client thread to panic it and also completes the outstanding client request to allow the kernel to perform the necessary cleanup
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enum TServerPanic { EPanicBadDescriptor, EPanicNotSupported }; void PanicClient(const RMessage& aMessage,TServerPanic aPanic) { _LIT(KPanic,"HerculesServer"); aMessagePanic(KPanic,aPanic); }
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A leave from CHerculeanSession::ServiceL() results in an early return from CServer::RunL(), which skips the call to continue requesting client messages From 11, you ll recall that, on receipt of a client request, CServer::RunL() calls the ServiceL() method of the associated CSharableSession-derived object It is for this reason that RunError() must call CServer::Restart() Moving on, let s consider the implementation of CHerculeanSession This consists of an implementation of the ServiceL() method, which was declared pure virtual in the CSharableSession base class, and a set of private methods to handle client requests:
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void CHerculeanSession::CreateL(const CServer& aServer) {// Called by the CServer framework CSharableSession::CreateL(aServer); // Cannot leave Server()AddSession(); // Create the CAsyncHandler object (iAsyncRequestHandler) } CHerculeanSession:: CHerculeanSession() { Server()RemoveSession(); delete iAsyncRequestHandler; delete iClientBuf; } // Handle a client request // Leaves are handled by CHerculeanServer::RunError() which is called // by CServer::RunL() void CHerculeanSession::ServiceL(const RMessage& aMessage)
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