Linux下Socket连接超时的一种实现方法

目前各平台通用的设置套接字（Socket）连接超时的办法是：

1. 创建套接字，将其设置成非阻塞状态。
2. 调用connect连接对端主机，如果失败，判断当时的errno是否为EINPROGRESS，也就是说是不是连接正在进行中，如果是，转到步骤3，如果不是，返回错误。
3. 用select在指定的超时时间内监听套接字的写就绪事件，如果select有监听到，证明连接成功，否则连接失败。

　　以下是Linux环境下的示例代码:


#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <time.h>

int main(int argc, char *argv[])
{
        int fd, retval;
        struct sockaddr_in addr;
        struct timeval timeo = {3, 0};
        socklen_t len = sizeof(timeo);
        fd_set set;

        fd = socket(AF_INET, SOCK_STREAM, 0);
        if (argc == 4)
                timeo.tv_sec = atoi(argv[3]);
        fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = inet_addr(argv[1]);
        addr.sin_port = htons(atoi(argv[2]));
        printf("%d/n", time(NULL));
        if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == 0) {
                printf("connected/n");
                return 0;
        }
        if (errno != EINPROGRESS) {
                perror("connect");
                return -1;
        }
        FD_ZERO(&set);
        FD_SET(fd, &set);
        retval = select(fd + 1, NULL, &set, NULL, &timeo);
        if (retval == -1) {
                perror("select");
                return -1;
        } else if(retval == 0) {
                fprintf(stderr, "timeout/n");
                printf("%d/n", time(NULL));
                return 0;
        }
        printf("connected/n");

        return 0;
}

 

[root@lanhai-linux CONNI]# ./coni 10.16.101.1 90
1223898556
timeout
1223898559
[root@lanhai-linux CONNI]# ./coni 10.16.101.1 90
1223898609
timeout
1223898612
[root@lanhai-linux CONNI]# ./coni 192.168.18.45
段错误
[root@lanhai-linux CONNI]# ./coni 192.168.18.45 90
1223898767

[root@lanhai-linux CONNI]# ./coni 192.168.18.37 80
1223898771
connected
[root@lanhai-linux CONNI]#