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我们知道, recv是一个阻塞的函数,没有到数据的时候,会傻傻地等待数据。那么怎么让recv函数有点脾气, 不傻傻地等待呢?
服务器为(先跑起来):
#include我们看到,当建立一个TCP连接后,服务器需要等3秒才发送数据,那么客户等得及吗?客户有耐心吗?且看客户:#include // winsock接口#pragma comment(lib, "ws2_32.lib") // winsock实现int main(){ WORD wVersionRequested; // 双字节,winsock库的版本 WSADATA wsaData; // winsock库版本的相关信息 wVersionRequested = MAKEWORD(1, 1); // 0x0101 即:257 // 加载winsock库并确定winsock版本,系统会把数据填入wsaData中 WSAStartup( wVersionRequested, &wsaData ); // AF_INET 表示采用TCP/IP协议族 // SOCK_STREAM 表示采用TCP协议 // 0是通常的默认情况 unsigned int sockSrv = socket(AF_INET, SOCK_STREAM, 0); SOCKADDR_IN addrSrv; addrSrv.sin_family = AF_INET; // TCP/IP协议族 addrSrv.sin_addr.S_un.S_addr = inet_addr("0.0.0.0"); addrSrv.sin_port = htons(8888); // socket对应的端口 // 将socket绑定到某个IP和端口(IP标识主机,端口标识通信进程) bind(sockSrv,(SOCKADDR*)&addrSrv, sizeof(SOCKADDR)); // 将socket设置为监听模式,5表示等待连接队列的最大长度 listen(sockSrv, 5); SOCKADDR_IN addrClient; int len = sizeof(SOCKADDR); while(1) { unsigned int sockConn = accept(sockSrv,(SOCKADDR*)&addrClient, &len); printf("accept is returned\n"); Sleep(3000); char sendBuf[100] = "hello"; send(sockConn, sendBuf, strlen(sendBuf) + 1, 0); // 发送数据到客户端,最后一个参数一般设置为0 //closesocket(sockConn); } closesocket(sockSrv); WSACleanup(); return 0;}
#include运行客户端程序,可以发现,尽管服务器故意延时了3秒,但客户有无限的耐心,仍然能收到数据。#include #pragma comment(lib, "ws2_32.lib")int main(){ WORD wVersionRequested; WSADATA wsaData; wVersionRequested = MAKEWORD(1, 1); WSAStartup( wVersionRequested, &wsaData ); SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0); SOCKADDR_IN addrSrv; addrSrv.sin_addr.S_un.S_addr = inet_addr("127.0.0.1"); addrSrv.sin_family = AF_INET; addrSrv.sin_port = htons(8888); int ret = connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)); printf("connect ret is %d\n", ret); char recvBuf[200] = "x"; ret = recv(sockClient, recvBuf, 100, 0); if(0 > ret) { printf("recv error"); return -3; } if(0 == ret) { printf("recv ret is %d\n", ret); return -4; } printf("%s\n", recvBuf); while(1); closesocket(sockClient); WSACleanup(); return 0;}
下面,我们来看看耐心有限的客户:
#include这个客户的耐心只有4秒,他发飙说:服务器,你妈的,在我跟你建立TCP关系后,你如果4秒之内没发数据,我就不鸟你了。运行程序,可以看到,这个客户依然可以接受到数据。#include #pragma comment(lib, "ws2_32.lib")int main(){ WORD wVersionRequested; WSADATA wsaData; wVersionRequested = MAKEWORD(1, 1); WSAStartup( wVersionRequested, &wsaData ); SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0); SOCKADDR_IN addrSrv; addrSrv.sin_addr.S_un.S_addr = inet_addr("127.0.0.1"); addrSrv.sin_family = AF_INET; addrSrv.sin_port = htons(8888); int ret = connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)); printf("connect ret is %d\n", ret); fd_set rfds; struct timeval timeout = { 4, 0}; FD_ZERO(&rfds); FD_SET(sockClient, &rfds); ret=select(-1, &rfds, NULL, NULL, &timeout); printf("select ret is %d\n",ret); if(0 > ret) { printf("select error\n"); return -1; } if(0 == ret) { printf("time out\n"); return -2; } if(FD_ISSET(sockClient, &rfds)) { char recvBuf[200] = "x"; ret = recv(sockClient, recvBuf, 100, 0); if(0 > ret) { printf("recv error"); return -3; } if(0 == ret) { printf("recv ret is %d, buf is %s\n", ret, recvBuf); return -4; } printf("%s\n", recvBuf); } while(1); closesocket(sockClient); WSACleanup(); return 0;}
下面我们再看看, 耐心只有2秒的客户:
#include这个客户的脾气够火爆啊,等了2秒,就不等了,所以就没有收到数据。#include #pragma comment(lib, "ws2_32.lib")int main(){ WORD wVersionRequested; WSADATA wsaData; wVersionRequested = MAKEWORD(1, 1); WSAStartup( wVersionRequested, &wsaData ); SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0); SOCKADDR_IN addrSrv; addrSrv.sin_addr.S_un.S_addr = inet_addr("127.0.0.1"); addrSrv.sin_family = AF_INET; addrSrv.sin_port = htons(8888); int ret = connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)); printf("connect ret is %d\n", ret); fd_set rfds; struct timeval timeout = { 2, 0}; FD_ZERO(&rfds); FD_SET(sockClient, &rfds); ret=select(-1, &rfds, NULL, NULL, &timeout); printf("select ret is %d\n",ret); if(0 > ret) { printf("select error\n"); return -1; } if(0 == ret) { printf("time out\n"); return -2; } if(FD_ISSET(sockClient, &rfds)) { char recvBuf[200] = "x"; ret = recv(sockClient, recvBuf, 100, 0); if(0 > ret) { printf("recv error"); return -3; } if(0 == ret) { printf("recv ret is %d, buf is %s\n", ret, recvBuf); return -4; } printf("%s\n", recvBuf); } while(1); closesocket(sockClient); WSACleanup(); return 0;}
在实际的软件开发中,常常要用到超时机制,可以避免客户端死等。
多的不闲扯了。最后,非常非常有趣的是:如果改为char recvBuf[2] = "x";
那么上面的各个程序会产生非常非常奇妙的结果,自己亲自研究一下吧!
靠,很晚了,睡觉。
分享一下我老师大神的人工智能教程。零基础!通俗易懂!风趣幽默!还带黄段子!希望你也加入到我们人工智能的队伍中来!
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