socket编程小问题：地址已经被使用——Address already in use

我也是刚开始学习socket网络编程，就在同学那搞到一个完整版的socket，我在centos上的eclipse下进行了编译，就是总出现Address already in use，后来发现了一篇博客，就是下文，试了试还是没用，结果就想一定是进程没有杀干净，所以就在eclipse下file里找到了restart，试了试果然好使！不过本人觉得下面一篇文章还是很好的！

 

 

 

 

很多socket编程的初学者可能会遇到这样的问题：如果先ctrl+c结束服务器端程序的话，再次启动服务器就会出现Address already in use这个错误，或者你的程序在正常关闭服务器端socket后还是有这个问题。正如下面的这段简单的socket程序。

 

server.c

#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>

#define BUFFER_SIZE 40

int main()
{
    char buf[BUFFER_SIZE];
    int server_sockfd, client_sockfd;
        int sin_size=sizeof(struct sockaddr_in);
    struct sockaddr_in server_address;
    struct sockaddr_in client_address;
    memset(&server_address,0,sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = INADDR_ANY;
    server_address.sin_port = htons(12000);
    // 建立服务器端socket
    if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0)
    {
        perror("server_sockfd creation failed");
        exit(EXIT_FAILURE);
    }
    // 将套接字绑定到服务器的网络地址上
    if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0)
    {
        perror("server socket bind failed");
        exit(EXIT_FAILURE);
    }
    // 建立监听队列
    listen(server_sockfd,5);
    // 等待客户端连接请求到达
    client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size);
    if(client_sockfd<0)
    {
        perror("accept client socket failed");
        exit(EXIT_FAILURE);
    }
    // 接收客户端数据
    if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0)
    {
        perror("recv client data failed");
        exit(EXIT_FAILURE);
    }
    printf("receive from client:%s/n",buf);
    // 发送数据到客户端
    if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0)
    {
        perror("send failed");
        exit(EXIT_FAILURE);
    }
    close(client_sockfd);
    close(server_sockfd);
    exit(EXIT_SUCCESS);
}

#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> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int server_sockfd, client_sockfd; int sin_size=sizeof(struct sockaddr_in); struct sockaddr_in server_address; struct sockaddr_in client_address; memset(&server_address,0,sizeof(server_address)); server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = INADDR_ANY; server_address.sin_port = htons(12000); // 建立服务器端socket if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0) { perror("server_sockfd creation failed"); exit(EXIT_FAILURE); } // 将套接字绑定到服务器的网络地址上 if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0) { perror("server socket bind failed"); exit(EXIT_FAILURE); } // 建立监听队列 listen(server_sockfd,5); // 等待客户端连接请求到达 client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size); if(client_sockfd<0) { perror("accept client socket failed"); exit(EXIT_FAILURE); } // 接收客户端数据 if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0) { perror("recv client data failed"); exit(EXIT_FAILURE); } printf("receive from client:%s/n",buf); // 发送数据到客户端 if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0) { perror("send failed"); exit(EXIT_FAILURE); } close(client_sockfd); close(server_sockfd); exit(EXIT_SUCCESS); }

 

client.c

#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>

#define BUFFER_SIZE 40

int main()
{
    char buf[BUFFER_SIZE];
    int client_sockfd;
    int len;
    struct sockaddr_in address;// 服务器端网络地址结构体
     int result;
    client_sockfd = socket(AF_INET, SOCK_STREAM, 0);// 建立客户端socket
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = inet_addr("127.0.0.1");
    address.sin_port = htons(12000);
    len = sizeof(address);
    // 与远程服务器建立连接
    result = connect(client_sockfd, (struct sockaddr *)&address, len);
    if(result<0)
    {
         perror("connect failed");
         exit(EXIT_FAILURE);
    }
    printf("Please input the message:");
    scanf("%s",buf);
    send(client_sockfd,buf,BUFFER_SIZE,0);
    recv(client_sockfd,buf,BUFFER_SIZE,0);
    printf("receive data from server: %s/n",buf);
    close(client_sockfd);
    return 0;
}

#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> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int client_sockfd; int len; struct sockaddr_in address;// 服务器端网络地址结构体 int result; client_sockfd = socket(AF_INET, SOCK_STREAM, 0);// 建立客户端socket address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr("127.0.0.1"); address.sin_port = htons(12000); len = sizeof(address); // 与远程服务器建立连接 result = connect(client_sockfd, (struct sockaddr *)&address, len); if(result<0) { perror("connect failed"); exit(EXIT_FAILURE); } printf("Please input the message:"); scanf("%s",buf); send(client_sockfd,buf,BUFFER_SIZE,0); recv(client_sockfd,buf,BUFFER_SIZE,0); printf("receive data from server: %s/n",buf); close(client_sockfd); return 0; }

 

      在成功的运行了第一次之后，当你再次启动服务器端程序时，./server就变得邪恶起来，在bind()这个函数中居然出现了Address already in use这个错误。

                                 

      然后你开始迷惑了，难道是忘记将socket给关闭了，或是关闭socket的顺序不对？经过种种猜测与试验，你发现问题毫无进展......过了一会，当你再次抱着试试看的态度重新在linux的“黑色终端”中输入./server时，程序居然运行了，什么情况？究其原因，是socket选项在捣鬼。下面是IBM官网上对这一情况的具体解释，参见http://www.ibm.com/developerworks/cn/linux/l-sockpit/。

      bind 普遍遭遇的问题是试图绑定一个已经在使用的端口。该陷阱是也许没有活动的套接字存在，但仍然禁止绑定端口（bind 返回 EADDRINUSE），它由 TCP 套接字状态 TIME_WAIT 引起。该状态在套接字关闭后约保留 2 到 4 分钟。在 TIME_WAIT 状态退出之后，套接字被删除，该地址才能被重新绑定而不出问题。

等待 TIME_WAIT 结束可能是令人恼火的一件事，特别是如果您正在开发一个套接字服务器，就需要停止服务器来做一些改动，然后重启。幸运的是，有方法可以避开 TIME_WAIT 状态。可以给套接字应用 SO_REUSEADDR 套接字选项，以便端口可以马上重用。

考虑清单 3 的例子。在绑定地址之前，我以 SO_REUSEADDR 选项调用 setsockopt。为了允许地址重用，我设置整型参数（on）为 1 （不然，可以设为 0 来禁止地址重用）。

      按照IBM的做法，我重新改写了server.c的代码。

server.c

 

#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>

#define BUFFER_SIZE 40

int main()
{
    char buf[BUFFER_SIZE];
    int server_sockfd, client_sockfd;
        int sin_size=sizeof(struct sockaddr_in);
    struct sockaddr_in server_address;
    struct sockaddr_in client_address;
    memset(&server_address,0,sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = INADDR_ANY;
    server_address.sin_port = htons(12000);
    // 建立服务器端socket
    if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0)
    {
        perror("server_sockfd creation failed");
        exit(EXIT_FAILURE);
    }
    // 设置套接字选项避免地址使用错误
    int on=1;
    if((setsockopt(server_sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)))<0)
    {
        perror("setsockopt failed");
        exit(EXIT_FAILURE);
    }
    // 将套接字绑定到服务器的网络地址上
    if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0)
    {
        perror("server socket bind failed");
        exit(EXIT_FAILURE);
    }
    // 建立监听队列
    listen(server_sockfd,5);
    // 等待客户端连接请求到达
    client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size);
    if(client_sockfd<0)
    {
        perror("accept client socket failed");
        exit(EXIT_FAILURE);
    }
    // 接收客户端数据
    if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0)
    {
        perror("recv client data failed");
        exit(EXIT_FAILURE);
    }
    printf("receive from client:%s/n",buf);
    // 发送数据到客户端
    if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0)
    {
        perror("send failed");
        exit(EXIT_FAILURE);
    }
    close(client_sockfd);
    close(server_sockfd);
    exit(EXIT_SUCCESS);
}

#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> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int server_sockfd, client_sockfd; int sin_size=sizeof(struct sockaddr_in); struct sockaddr_in server_address; struct sockaddr_in client_address; memset(&server_address,0,sizeof(server_address)); server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = INADDR_ANY; server_address.sin_port = htons(12000); // 建立服务器端socket if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0) { perror("server_sockfd creation failed"); exit(EXIT_FAILURE); } // 设置套接字选项避免地址使用错误 int on=1; if((setsockopt(server_sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)))<0) { perror("setsockopt failed"); exit(EXIT_FAILURE); } // 将套接字绑定到服务器的网络地址上 if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0) { perror("server socket bind failed"); exit(EXIT_FAILURE); } // 建立监听队列 listen(server_sockfd,5); // 等待客户端连接请求到达 client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size); if(client_sockfd<0) { perror("accept client socket failed"); exit(EXIT_FAILURE); } // 接收客户端数据 if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0) { perror("recv client data failed"); exit(EXIT_FAILURE); } printf("receive from client:%s/n",buf); // 发送数据到客户端 if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0) { perror("send failed"); exit(EXIT_FAILURE); } close(client_sockfd); close(server_sockfd); exit(EXIT_SUCCESS); }

       这次，让我们再次反复的启动服务器，尽情的在“黑窗户”里面输入./server ./server ./server ......服务器的程序好像突然间变乖了，呵呵，童鞋们，为自己的成就庆祝吧！！！