一个关于socket在非阻塞模式下connect是否成功的例子

一个关于socket在非阻塞模式下connect是否成功的例子

void connect_w_to(void) { int res; struct sockaddr_in addr; long arg; fd_set myset; struct timeval tv; int valopt; socklen_t lon; // Create socket soc = socket(AF_INET, SOCK_STREAM, 0); if (soc < 0) { fprintf(stderr, "Error creating socket (%d %s)\n", errno, strerror(errno)); exit(0); } addr.sin_family = AF_INET; addr.sin_port = htons(2000); addr.sin_addr.s_addr = inet_addr("192.168.0.1"); // Set non-blocking if( (arg = fcntl(soc, F_GETFL, NULL)) < 0) { fprintf(stderr, "Error fcntl(..., F_GETFL) (%s)\n", strerror(errno)); exit(0); } arg |= O_NONBLOCK; if( fcntl(soc, F_SETFL, arg) < 0) { fprintf(stderr, "Error fcntl(..., F_SETFL) (%s)\n", strerror(errno)); exit(0); } // Trying to connect with timeout res = connect(soc, (struct sockaddr *)&addr, sizeof(addr)); if (res < 0) { if (errno == EINPROGRESS) { fprintf(stderr, "EINPROGRESS in connect() - selecting\n"); do { tv.tv_sec = 15; tv.tv_usec = 0; FD_ZERO(&myset); FD_SET(soc, &myset); res = select(soc+1, NULL, &myset, NULL, &tv); if (res < 0 && errno != EINTR) { fprintf(stderr, "Error connecting %d - %s\n", errno, strerror(errno)); exit(0); } else if (res > 0) { // Socket selected for write lon = sizeof(int); if (getsockopt(soc, SOL_SOCKET, SO_ERROR, (void*)(&valopt), &lon) < 0) { fprintf(stderr, "Error in getsockopt() %d - %s\n", errno, strerror(errno)); exit(0); } // Check the value returned... if (valopt) { fprintf(stderr, "Error in delayed connection() %d - %s\n", valopt, strerror(valopt) ); exit(0); } break; } else { fprintf(stderr, "Timeout in select() - Cancelling!\n"); exit(0); } } while (1); } else { fprintf(stderr, "Error connecting %d - %s\n", errno, strerror(errno)); exit(0); } } // Set to blocking mode again... if( (arg = fcntl(soc, F_GETFL, NULL)) < 0) { fprintf(stderr, "Error fcntl(..., F_GETFL) (%s)\n", strerror(errno)); exit(0); } arg &= (~O_NONBLOCK); if( fcntl(soc, F_SETFL, arg) < 0) { fprintf(stderr, "Error fcntl(..., F_SETFL) (%s)\n", strerror(errno)); exit(0); } // I hope that is all }

简单的说就是：

To do a non-blocking connect(), assuming the socket has already been made non-blocking: int res = connect(fd, ...); if (res < 0 && errno != EINPROGRESS) { // error, fail somehow, close socket return; } if (res == 0) { // connection has succeeded immediately } else { // connection attempt is in progress } For the second case, where connect() failed with EINPROGRESS (and only in this case), you have to wait for the socket to be writable, e.g. for epoll specify that you're waiting for EPOLLOUT on this socket. Once you get notified that it's writable (with epoll, also expect to get an EPOLLERR or EPOLLHUP event), check the result of the connection attempt: int result; socklen_t result_len = sizeof(result); if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &result, &result_len) < 0) { // error, fail somehow, close socket return; } if (result != 0) { // connection failed; error code is in 'result' return; } // socket is ready for read()/write()

在网上找到这么一个实现方法,不知道对不对,或者有没有更好的解释,更好的方法 网上是这样说的,方案是使用select 1.将打开的socket设为非阻塞的 2.发connect调用,这时返回-1,但是errno被设为EINPROGRESS,意即connect仍旧在进行还没有完成.  3.将打开的socket设进被监视的可写(注意不是可读)文件集合用select进行监视, 如果可写,用 getsockopt(socket, SOL_SOCKET, SO_ERROR, 来得到error的值,如果为零,则connect成功