網(wǎng)絡(luò)編程Socket之UDP三超時設(shè)置和非阻塞

1、網(wǎng)絡(luò)編程 Socket 之 UDP（ 三 ）超時設(shè)置和非阻塞前面遺留的兩個問題：1. 一個已連接 UDP 套接字能且僅能與一個對端交換數(shù)據(jù)報， 那么客戶端發(fā)送廣播的時候如何防止 recvfrom 方法阻塞；2. 服務(wù)端忙的時候，已連接的 UDP 套接字也會被阻塞。 方法一：設(shè)置超時UNP 14.2There are three ways to place a timeout on an I/Ooperation involving a socket:1.Callalarm, which generates theSIGALRMsignal when the specified time has

2、expired. This involves signal handling, which can differ from oneimplementation to the next, and it may interfere with other existing calls toalarmin the process.2.Block waiting for I/O inselect, which has a time limit built-in, instead ofblocking in a call toread orwrite.3. Use the newerSO_RCVTIMEO

3、 andSO_SNDTIMEO socket options. The problemwith this approach is that not all implementations support these two socket options.第一種方法我們可以用 ios 提供的定時器來實(shí)現(xiàn)； 第二種方法在 recvfrom 方法調(diào)用前添加代碼如下， 這里是設(shè) 置 3 秒超時：cpp view plain copy <span style=font-size:12px;> fd_set read_fdset;struct timeval timeout;FD_ZERO(&

4、amp;read_fdset);FD_SET(socketFileDescriptor, &read_fdset); timeout.tv_sec = 3;timeout.tv_usec = 0;int ret; do ret = select(socketFileDescriptor + 1, &read_fdset, NULL,NULL, &timeout); while (ret <if0 && errno = EINTR);(ret = 0) printf(time outn);return -1; </span>第三種方法代碼

5、如下：cpp view plain copy <span style=font-size:12px;> struct timeval timeout = 3,0;setsockopt(socketFileDescriptor, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeout, sizeof(structtimeval);</span> 設(shè)置 3 秒超時，如果 3 秒以后無法 讀到數(shù)據(jù)， recvfrom 方法返回 -1 ，而且 errno 返回 EWOULDBLOCK 錯誤cpp view plain copy <spa

6、n style=font-size:12px;> n = recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL); if (n < 0) if (errno = EWOULDBLOCK) printf(time outn); return -1; else err_sys(recvfrom error); </span> 方法二： 使 用非阻塞式 IOUNP 16.1With a nonblocking socket, if the input operation cannot be satisfied (at leasto

7、ne byte of data for a TCP socket or a complete datagram for a UDP socket),we see animmediate return with an error of EWOULDBLOCK. 首先 設(shè)置非阻塞套接字：cpp view plain copy <span style=font-size:12px;> int ret; int flags = fcntl(socketFileDescriptor,F_GETFL);if (flags = -1)printf(fcntl error);return -1;f

8、lags |= O_NONBLOCK;ret =fcntl(socketFileDescriptor, F_SETFL, flags);if (ret =-1)printf(fcntl error);return-1; </span> 然后運(yùn)行， 打印信息如下： >> send success>> recvfrom fail-errno = 35>> send success>> recvfrom fail-errno = 35>> send success>> recvfrom fail-errno = 35

9、>> send success>> recvfrom fail-errno = 35>> send success>> server said:01&c0:5e:79:fc:0e:0c&192.168.0.1&iS hare-R1B011D2199>> send success>> recvfrom fail-errno = 35>> send success>> recvfrom fail-errno = 35>> send success>> re

10、cvfrom fail-errno = 35 會發(fā)現(xiàn) recvfrom 方法返 回失敗的概率很大， 而且 errno 返回 EWOULDBLOCK 錯誤， 這是因?yàn)樵诜亲枞那闆r下有可能因?yàn)榉?wù)器阻塞導(dǎo)致客 戶端這邊的 UDP 套接字的接收緩沖區(qū)為空， 因此為了解決 這個問題我們在 recvfrom 方法之前添加如下代碼：cpp view plain copy <span style=font-size:12px;> fd_set read_fdset;FD_ZERO(&read_fdset);FD_SET(socketFileDescriptor, &read_f

11、dset);int ret; do ret = select(socketFileDescriptor + 1, &read_fdset, NULL, NULL, NULL); while (ret < 0 && errno = EINTR);if (ret= 0) printf(time outn);return -1; </span> 然后運(yùn)行，打印信息如 下： >> send success>> server said:01&c0:5e:79:fc:0e:0c&192.168.0.1&iS hare

12、-R1B011D2199>> send success>> serversaid:01&c0:5e:79:fc:0e:0c&192.168.0.1&iS hare-R1B011D2199>> send success>> serversaid:01&c0:5e:79:fc:0e:0c&192.168.0.1&iS hare-R1B011D2199>> send success>> serversaid:01&c0:5e:79:fc:0e:0c&192.168.0.1&iS hare-R1B011D