借助于网上他人文章，研究 SO_KEEPLIVE 问题：http://www.iteye.com/topic/1118643
client端加了 setsockopt 函数调用。看看能否在服务器端未启动时，或下线时候，一直等待两小时左右。
#include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> int main(){ int sockfd; int len; struct sockaddr_in address; int result; int i,byte; char char_recv,char_send;int optval; socklen_t optlen = sizeof(optval); if((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1){ perror("socket"); exit(EXIT_FAILURE); } /* Set the option active */ optval = 1; optlen = sizeof(optval); if(setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0){ perror("setsockopt()"); close(s); exit(EXIT_FAILURE); } address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr("127.0.0.1"); address.sin_port = 8080; len = sizeof(address); if((result = connect(sockfd,(struct sockaddr *)&address,len)) == -1){ perror("connect"); exit(EXIT_FAILURE); } printf("please enter the context you want to send to server :"); scanf("%c",&char_send); if(byte = send(sockfd,&char_send,1,0) == -1){ perror("send"); exit(EXIT_FAILURE); } if(byte = recv(sockfd,&char_recv,1,0) == -1){ perror("recv"); exit(EXIT_FAILURE); } printf("receive from server %c\n",char_recv); close(sockfd); exit(0); }
服务器端逻辑不变：
#include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> char dict(char temp){ if(temp == 'Z'){ return 'A'; } return temp+1; } int main(){ int server_sockfd,client_sockfd; int server_len,client_len; struct sockaddr_in server_address; struct sockaddr_in client_address; int i,btye; char char_recv,char_send; server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = inet_addr("127.0.0.1"); server_address.sin_port = 8080; server_len = sizeof(server_address); server_sockfd = socket(AF_INET,SOCK_STREAM,0);bind(server_sockfd,(struct sockaddr *)&server_address,server_len); listen(server_sockfd,5); printf("server waiting for connect\n"); client_len = sizeof(client_address); client_sockfd = accept(server_sockfd,
(struct sockaddr *)&client_address,(socklen_t *)&client_len);if(btye = recv(client_sockfd,&char_recv,1,0) == -1){ perror("recv"); exit(EXIT_FAILURE); } printf("receive from client is %c\n",char_recv); char_send = dict(char_recv); if(btye = send(client_sockfd,&char_send,1,0) == -1){ perror("send"); exit(EXIT_FAILURE); } shutdown(client_sockfd,2); shutdown(server_sockfd,2); return 0; }
试验结果表明，SO_KEEPLIVE 设定，对此情形无效。