Windows Socket Message-Driven/WSAAsyncSelect Model. Prof. Lin Weiguo Copyleft 2009~2015, College of Computing, CUC

Transcription

1 Windows Socket Message-Driven/WSAAsyncSelect Model Prof. Lin Weiguo Copyleft 2009~2015, College of Computing, CUC Dec 2015

2 Note You should not assume that an example in this presentation is complete. Items may have been selected for illustration. It is best to get your code examples directly from the textbook and modify them to work. Use the lectures to understand the general principles. 2 Advanced Windows Network Programming

3 Windows Message Processing Windows Messages Windows-based applications are event-driven. They do not make explicit function calls to obtain input. Instead, they wait for the system to pass input to them. The system passes input to a window procedure in the form of messages. Messages are generated by both the system and applications. How a Single-Threaded Program Processes Messages MSG message; while (::GetMessage(&message, NULL, 0, 0)) { ::TranslateMessage(&message); ::DispatchMessage(&message); 3 Advanced Windows Network Programming

4 Message-driven Execution (Asynchronous): 4 Advanced Windows Network Programming

5 Message-Driven I/O Windows specific variant of non-blocking I/O The I/O functions continue to run in the background and the program is notified if: I/O operations are completed I/O operations can be executed An I/O error occurred Notification is done using window messages. Each Windows application (must have a GUI) has a message loop that processes window messages and other messages When we use Message-Driven I/O, we define a custom message that is sent to the message loop to notify us about the status of IO operations. 5 Advanced Windows Network Programming

6 Message Flow 6 Advanced Windows Network Programming

7 Win32 API Message Processing Every Window element has an associated Window Procedure - registered when the Window is created, for processing messages. LRESULT WndProc(HWND hwnd, UINT imessage, WPARAM wparam, LPARAM lparam ) { switch (imessage) { case WM_CREATE: DoCreate(); break; case WM_PAINT: Paint(); break; case WM_DESTROY: PostQuitMessage( 0 ); break; default: return DefWindowProc( hwnd, imessage, wparam, lparam ); return 0; 7 Advanced Windows Network Programming

8 MFC: Message Mapping Macro // Example for BEGIN_MESSAGE_MAP BEGIN_MESSAGE_MAP( CMyWindow, CFrameWnd ) ON_WM_PAINT() ON_COMMAND( IDM_ABOUT, OnAbout ) END_MESSAGE_MAP( ) BEGIN_MESSAGE_MAP(CComputeDlg, CDialog) ON_BN_CLICKED(IDC_START, &CComputeDlg::OnBnClickedStart) ON_BN_CLICKED(IDC_CANCEL, &CComputeDlg::OnBnClickedCancel) ON_WM_TIMER() END_MESSAGE_MAP() 8 Advanced Windows Network Programming

9 Create Message-driven Socket Winsock provides a useful asynchronous I/O model that allows an application to receive Windows message based notification of network events on a socket. This is accomplished by calling the WSAAsyncSelect function after creating a socket. Create Message-driven Socket Step 1: Create a socket as usual. Step 2: Use the WSAAsyncSelect function to turn the socket into a message-driven socket. Note: The WSAAsyncSelect and WSAEventSelect models provide asynchronous notification of the capability to read or write data. It does not provide asynchronous data transfer like the overlapped and completion port models. 9 Advanced Windows Network Programming

10 WSAAsyncSelect The WSAAsyncSelect function requests Windows message-based notification of network events for a socket. int WSAAsyncSelect( in SOCKET s, in HWND hwnd, in unsigned int wmsg, in long levent ); Parameters s [in]: A descriptor that identifies the socket for which event notification is required. hwnd [in] A handle that identifies the window that will receive a message when a network event occurs. wmsg [in] A message to be received when a network event occurs. levent [in] A bitmask that specifies a combination of network events in which the application is interested. Note: socket() creates a socket in blocking mode, WSAAsyncSelect() turns it to non-blocking mode. 10 Advanced Windows Network Programming

11 User-Defined Winsock Message Declare user message ID #define WM_WINSOCK (WM_USER + 100) Declare message handling function in the.h file afx_msg LRESULT OnWinsock(WPARAM wparam, LPARAM lparam); DECLARE_MESSAGE_MAP() Map the message to the handling function in.cpp file BEGIN_MESSAGE_MAP(CMYDlg, CDialog) ON_MESSAGE(WM_WINSOCK, OnWinsock) END_MESSAGE_MAP() Implement the message handling functon in.cpp file LRESULT CMyDlg::OnWinsock(WPARAM wparam, LPARAM lparam) {... return 0; 11 Advanced Windows Network Programming

12 Winsock Message Posting 12 Advanced Windows Network Programming

13 Posting winsock message int CMyDlg::StartMsgDrivenReceive() { //... int err = WSAAsyncSelect ( socket, m_hwnd, WM_WINSOCK, FD_READ FD_ACCEPT FD_CLOSE); if (err!= 0) { afxmessagebox("wsaasyncselect() failed! ); //... //... // Window handle, from MFC s CWindow 13 Advanced Windows Network Programming

14 Network Event Types for the WSAAsyncSelect Function Event Type FD_READ FD_WRITE FD_OOB FD_ACCEPT FD_CONNECT FD_CLOSE FD_QOS Meaning The application wants to receive notification of readiness for reading. The application wants to receive notification of readiness for writing. The application wants to receive notification of the arrival of OOB data. The application wants to receive notification of incoming connections. The application wants to receive notification of a completed connection or a multipoint join operation. The application wants to receive notification of socket closure. The application wants to receive notification of socket QOS changes. FD_GROUP_QOS FD_ROUTING_INTE RFACE_CHANGE FD_ADDRESS_LIST_ CHANGE The application wants to receive notification of socket group QOS changes (reserved for future use with socket groups). The application wants to receive notification of routing interface changes for the specified destination(s). The application wants to receive notification of local address list changes for the socket's protocol family. 14 Advanced Windows Network Programming

15 Setting the Event parameter WSAAsyncSelect(Sockfd, m_hwnd, WM_SOCKET, FD_READ FD_WRITE); // Activate both read & write. WSAAsyncSelect(Sockfd, hmywindow, WM_SOCKET, 0 // Disable all events. ); //a typical client WSAAsyncSelect(s, m_hwnd, WM_SOCKET, FD_CONNECT FD_READ FD_WRITE FD_CLOSE ); 15 Advanced Windows Network Programming

16 Server side WSAAsyncSelect SOCKET Listen = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP); // Bind the socket to port 5150 and begin listening for connections InternetAddr.sin_family = AF_INET; InternetAddr.sin_addr.s_addr = htonl(inaddr_any); InternetAddr.sin_port = htons(5150); bind(listen, (PSOCKADDR) &InternetAddr, sizeof(internetaddr)); // Set up window message notification on // the new socket using the WM_SOCKET define above WSAAsyncSelect(Listen, Window, WM_SOCKET, FD_ACCEPT FD_CLOSE); listen(listen, 5); // Translate and dispatch window messages // until the application terminates while (1) { // Advanced Windows Network Programming

17 Processing Winsock Message LRESULT CMyDlg::OnWinsock(WPARAM wparam, LPARAM lparam) { SOCKET sock = (SOCKET) wparam; int event = WSAGETSELECTEVENT(lParam); int WsaErr = WSAGETSELECTERROR(lParam); // Determine whether an error occurred on the socket by using the WSAGETSELECTERROR() macro if (WsaErr) { closesocket( sock ); return 0; switch(event)// Determine what event occurred on the socket { case FD_ACCEPT: OnAccept( sock ); break; // Accept an incoming connection case FD_READ: OnRead( sock ); break; // Receive data from the socket in wparam case FD_WRITE: OnWrite( sock ); break; // The socket in wparam is ready for sending data case FD_CLOSE: closesocket( sock); break; // The connection is now closed return 0; 17 Advanced Windows Network Programming

18 Processing Winsock Event:OnAccept() Void CMyDlg::OnAccept(SOCKET mysocket) { SOCKET AcceptedSock = accept(mysocket, NULL, NULL); if (total_conn >= MAX_CLIENT_NUM) //close if more than MAX client number { closesocket(acceptedsock); return; ClientSock[CurConn].Sock=AcceptedSock; //save the new socket to the connected list // Prepare accepted socket for read, write, and close notification WSAAsyncSelect(AcceptedSock, m_hwnd, WM_SOCKET, FD_READ FD_WRITE FD_CLOSE); Void CMyDlg::OnRead(SOCKET mysocket) { if (mysocket==serversock_udp) //UDP Echo { recvfrom( ); sendto( ); else if (mysocket!=serversock) //TCP Time server { recv( ); send( ); 18 Advanced Windows Network Programming

19 Alternative way for processing User-Defined Message Step 1: Select the dialog class in the Class view. Step 2: Go to Properties view. Click the icon for overrides (a green cube in VS.NET 2008). Find Window Proc in the list. Open the drop-list and select <Add> Window Proc. 19 Advanced Windows Network Programming

20 Alternative way for processing User-Defined Message Step 3: Add code to filter the defined custom message for network events // Override MFC's Window procedure to process the Winsock messages. LRESULT CMyDlg::WindowProc(UINT message, WPARAM wparam, LPARAM lparam) { // TODO: Add your specialized code here and/or call the base class if (message == WM_WINSOCK) { int event = WSAGETSELECTEVENT(lParam); int wsaerr = WSAGETSELECTERROR(lParam); switch (event) { case FD_READ : OnRead(); return 0; case FD_ACCEPT : OnAccept(); return 0; case FD_CLOSE : OnClose(); return 0; return CDialog::WindowProc(message, wparam, lparam); 20 Advanced Windows Network Programming

21 Winsock Event Triggering Edge-Triggered v.s. Level Triggered Re-enabling functions 21 Advanced Windows Network Programming

22 Winsock Event Triggering Level Trigger example: FD_READ 22 Advanced Windows Network Programming

23 Winsock Event Triggering Edge Trigger example: FD_WRITE 23 Advanced Windows Network Programming

24 On Write case FD_WRITE: // write event { while(true) { // read from a file into packet.data. in.read((char*)&packet.data, MAX_PACKET_SIZE); // sending data if (send(wparam, (char*)(&packet), sizeof(packet), 0) == SOCKET_ERROR) { if (WSAGetLastError() == WSAEWOULDBLOCK) { break; // socket internal buffer full else // other errors { // output error message, and return. CleanUp(); return(0); break; 24 Advanced Windows Network Programming

25 summary of events and conditions for asynchronous notification message. FD_READ: 1. When WSAAsyncSelect is called, if there is data currently available to receive. 2. When data arrives, if FD_READ is not already posted. 3. After recv or recvfrom is called, with or without MSG_PEEK, if data is still available to receive. FD_WRITE: 1. When WSAAsyncSelect called, if a send or sendto is possible. 2. After connect or accept called, when connection established. 3. After send or sendto fail with WSAEWOULDBLOCK, when send or sendto are likely to succeed. 4. After bind on a connectionless socket. FD_WRITE may or may not occur at this time (implementation-dependent). In any case, a connectionless socket is always writeable immediately after a bind operation. 25 Advanced Windows Network Programming

26 summary of events and conditions for asynchronous notification message. FD_ACCEPT: 1. When WSAAsyncSelect called, if there is currently a connection request available to accept. 2. When a connection request arrives, if FD_ACCEPT not already posted. 3. After accept called, if there is another connection request available to accept. FD_CONNECT: 1. When WSAAsyncSelect called, if there is currently a connection established. 2. After connect called, when connection is established, even when connect succeeds immediately, as is typical with a datagram socket. 3. After calling WSAJoinLeaf, when join operation completes. 4. After connect, WSAConnect, or WSAJoinLeaf was called with a nonblocking, connection-oriented socket. The initial operation returned with a specific error of WSAEWOULDBLOCK, but the network operation went ahead. Whether the operation eventually succeeds or not, when the outcome has been determined, FD_CONNECT happens. The client should check the error code to determine whether the outcome was successful or failed. 26 Advanced Windows Network Programming

27 summary of events and conditions for asynchronous notification message. FD_CLOSE: Only valid on connection-oriented sockets (for example, SOCK_STREAM) 1. When WSAAsyncSelect called, if socket connection has been closed. 2. After remote system initiated graceful close, when no data currently available to receive (Be aware that, if data has been received and is waiting to be read when the remote system initiates a graceful close, the FD_CLOSE is not delivered until all pending data has been read). 3. After local system initiates graceful close with shutdown and remote system has responded with "End of Data" notification (for example, TCP FIN), when no data currently available to receive. 4. When remote system terminates connection (for example, sent TCP RST), and lparam will contain WSAECONNRESET error value. Note FD_CLOSE is not posted after closesocket is called. 27 Advanced Windows Network Programming

28 Message-Driven Concurrent Server 28 Advanced Windows Network Programming

29 Summary The WSAAsyncSelect model offers many advantages foremost is the capability to handle many connections simultaneously without much overhead, unlike the select model's requirement of setting up the fd_set structures. The disadvantages are having to use a window if your application requires no windows (such as a service or console application). Also, having a single window procedure to service all the events on thousands of socket handles can become a performance bottleneck (meaning this model doesn't scale very well). 29 Advanced Windows Network Programming

30 references Programming With Microsoft Visual C++ NET 6 th Ed. - George/Kruglinski Shepherd Network Programming for Microsoft Windows, 2nd Ed. - Anthony Jones, Jim Ohlund MSDN: WSAAsyncSelect, WSAEventSelect Function CUHK Ieg4180: Network Software Design and Programming Drew Sikora, Programming with Asynchronous Sockets, GameDev.net, 2/1/ The C10K problem, 30 Advanced Windows Network Programming