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  • Preventing FIN_WAIT2 when closing socket

    - by patrickvacek
    I have a server program that connects to another program via a given socket, and in certain cases I need to close the connection and almost immediately re-open it on the same socket. This by and large works, except that I have to wait exactly one minute for the socket to reset. In the meantime, netstat indicates that the server sees the socket in FIN_WAIT2 and the client sees it as CLOSE_WAIT. I'm already using SO_REUSEADDR, which I thought would prevent the wait, but that isn't doing the trick. Setting SO_LINGER to zero also does not help. What else can I do to resolve this? Here are the relevant code snippets: SetUpSocket() { // Set up the socket and listen for a connection from the exelerate client. // Open a TCP/IP socket. m_baseSock = socket(PF_INET, SOCK_STREAM, IPPROTO_IP); if (m_baseSock < 0) { return XERROR; } // Set the socket options to reuse local addresses. int flag = 1; if (setsockopt(m_baseSock, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag)) == -1) { return XERROR; } // Set the socket options to prevent lingering after closing the socket. //~ linger li = {1,0}; //~ if (setsockopt(m_baseSock, SOL_SOCKET, SO_LINGER, &li, sizeof(li)) == -1) //~ { //~ return XERROR; //~ } // Bind the socket to the address of the current host and our given port. struct sockaddr_in addr; memset(&addr, 0, sizeof(addr)); addr.sin_family = AF_INET; addr.sin_addr.s_addr = INADDR_ANY; addr.sin_port = htons(m_port); if (bind(m_baseSock, (struct sockaddr*)&addr, sizeof(addr)) != 0) { return XERROR; } // Tell the socket to listen for a connection from client. if (listen(m_baseSock, 4) != 0) { return XERROR; } return XSUCCESS; } ConnectSocket() { // Add the socket to a file descriptor set. fd_set readfds; FD_ZERO(&readfds); FD_SET(m_baseSock, &readfds); // Set timeout to ten seconds. Plenty of time. struct timeval timeout; timeout.tv_sec = 10; timeout.tv_usec = 0; // Check to see if the socket is ready for reading. int numReady = select(m_baseSock + 1, &readfds, NULL, NULL, &timeout); if (numReady > 0) { int flags = fcntl(m_baseSock, F_GETFL, 0); fcntl(m_baseSock, flags | O_NONBLOCK, 1); // Wait for a connection attempt from the client. Do not block - we shouldn't // need to since we just selected. m_connectedSock = accept(m_baseSock, NULL, NULL); if (m_connectedSock > 0) { m_failedSend = false; m_logout = false; // Spawn a thread to accept commands from client. CreateThread(&m_controlThread, ControlThread, (void *)&m_connectedSock); return XSUCCESS; } } return XERROR; } ControlThread(void *arg) { // Get the socket from the argument. socket sock = *((socket*)arg); while (true) { // Add the socket to a file descriptor set. fd_set readfds; FD_ZERO(&readfds); FD_SET(sock, &readfds); // Set timeout to ten seconds. Plenty of time. struct timeval timeout; timeout.tv_sec = 10; timeout.tv_usec = 0; // Check if there is any readable data on the socket. int num_ready = select(sock + 1, &readfds, NULL, NULL, &timeout); if (num_ready < 0) { return NULL; } // If there is data, read it. else if (num_ready > 0) { // Check the read buffer. xuint8 buf[128]; ssize_t size_read = recv(sock, buf, sizeof(buf)); if (size_read > 0) { // Get the message out of the buffer. char msg = *buf; if (msg == CONNECTED) { // Do some things... } // If we get the log-out message, log out. else if (msg == LOGOUT) { return NULL; } } } } // while return NULL; } ~Server() { // Close the sockets. if (m_baseSock != SOCKET_ERROR) { close(m_baseSock); m_baseSock = SOCKET_ERROR; } if (m_connectedSock != SOCKET_ERROR) { close(m_connectedSock); m_connectedSock = SOCKET_ERROR; } } SOCKET_ERROR is equal to -1. The server object gets destroyed, at which point the connection should close, and then recreated, at which point the SetUpSocket() and ConnectSocket() routines are called. So why do I have to wait a minute for the socket to clear? Any ideas would be appreaciated.

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