服务器与客户端连接，客户端异常断掉之后服务器端口仍然被占用， 到最后是不是服务器端达到最大连接数就没法连接了？领导让我测试这种情况，我用自己的电脑当TCP Client，虚拟机当服务器，连接之后能正常通信，每次拔掉网线断开，5次之后就不能连接了（我的服务器设置最大连接数就是5）。具体如下：1：用模拟软件Commix模拟TCP Client，连接服务器。
2：用服务器端监听端口1234。重复打开关闭TCP Client的端口，服务器显示如下图所示：
1——5次可以正常连接，5次完成之后出现如下问题：
请问怎么解决这一问题，让服务器端自动清除已断掉的连接。
socket程序如下所示：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define MYPORT 1234 // the port users will be connecting to
#define BACKLOG 5 // how many pending connections queue will hold
#define BUF_SIZE 200
int fd_A[BACKLOG]; // accepted connection fd
int conn_amount; // current connection amount
void showclient()
{
int i;
printf("client amount: %d\n", conn_amount);
for (i = 0; i < BACKLOG; i++) {
printf("[%d]:%d ", i, fd_A);
}
printf("\n\n");
}
int main(void)
{
int sock_fd, new_fd; // listen on sock_fd, new connection on new_fd
struct sockaddr_in server_addr; // server address information
struct sockaddr_in client_addr; // connector‘s address information
socklen_t sin_size;
int yes = 1;
char buf[BUF_SIZE];
int ret;
int i;
if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(1);
}
if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
server_addr.sin_family = AF_INET; // host byte order
server_addr.sin_port = htons(MYPORT); // short, network byte order
server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
memset(server_addr.sin_zero, ‘\0‘, sizeof(server_addr.sin_zero));
if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
perror("bind");
exit(1);
}
if (listen(sock_fd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
printf("listen port %d\n", MYPORT);
fd_set fdsr;
int maxsock;
struct timeval tv;
conn_amount = 0;
sin_size = sizeof(client_addr);
maxsock = sock_fd;
while (1) {
// initialize file descriptor set
FD_ZERO(&fdsr);
FD_SET(sock_fd, &fdsr);
// timeout setting
tv.tv_sec = 30;
tv.tv_usec = 0;
// add active connection to fd set
for (i = 0; i < BACKLOG; i++) {
if (fd_A != 0) {
FD_SET(fd_A, &fdsr);
}
}
ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv);
if (ret < 0) {
perror("select");
break;
} else if (ret == 0) {
printf("timeout\n");
continue;
}
// check every fd in the set
for (i = 0; i < conn_amount; i++) {
if (FD_ISSET(fd_A, &fdsr)) {
ret = recv(fd_A, buf, sizeof(buf), 0);
if (ret <= 0) { // client close
printf("client[%d] close\n", i);
close(fd_A);
FD_CLR(fd_A, &fdsr);
fd_A = 0;
} else { // receive data
if (ret < BUF_SIZE)
memset(&buf[ret], ‘\0‘, 1);
printf("client[%d] send:%s\n", i, buf);
}
}
}
// check whether a new connection comes
if (FD_ISSET(sock_fd, &fdsr)) {
new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size);
if (new_fd <= 0) {
perror("accept");
continue;
}
// add to fd queue
if (conn_amount < BACKLOG) {
fd_A[conn_amount++] = new_fd;
printf("new connection client[%d] %s:%d\n", conn_amount,
inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
if (new_fd > maxsock)
maxsock = new_fd;
}
else {
printf("max connections arrive, exit\n");
send(new_fd, "bye", 4, 0);
close(new_fd);
break;
}
}
showclient();
}
// close other connections
for (i = 0; i < BACKLOG; i++) {
if (fd_A != 0) {
close(fd_A);
}
}
exit(0);
}
原文地址：http://yzkwork.blog.51cto.com/9291482/1620768
