实例分析1
将服务器端的listen函数backlog设置为2，用20个客户端与服务器建立连接，查看连接的建立情况。
服务器代码：
#include <stdio.h>
#include<unistd.h>
#include<sys/types.h> /* basic system data types */
#include<sys/socket.h> /* basic socket definitions */
#include<netinet/in.h> /* sockaddr_in{} and other Internet defns */
#include<arpa/inet.h> /* inet(3) functions */
#include<sys/epoll.h> /* epoll function */
#include<fcntl.h>
#include<stdlib.h>
#include<errno.h>
#include<stdio.h>
#include<string.h>
int main(int argc,char*argv[])
{
int listenfd,connfd;
struct sockaddr_in cliaddr,servaddr;
int queuelen=5;
if(argc!=2){
puts("usage# ./aworker listenqueuelen");
exit(0);
}
queuelen=atoi(argv[1]);
listenfd = socket(AF_INET,SOCK_STREAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(2989);
bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
listen(listenfd,queuelen);
sleep(60); //将这个注释，会出现另一种情况哟~~
while(1)
{
connfd = accept(listenfd,NULL,0);
if(connfd == -1)
{
perror("accept error");
continue;
}
puts("new connection...");
}
return 0;
}
client代码
#include "client.h"
//void cli_hander(int sockfd,)
int main()
{
int sockfd;
int rc;
int cpid;
struct sockaddr_in servaddr;
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
inet_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr);
servaddr.sin_port = htons(2989);
for(int i=0;i<20;i++)
{
cpid = fork();
if(cpid == 0)
{
sockfd = socket(AF_INET,SOCK_STREAM,0);
rc = connect(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
if(rc == -1)
{
perror("connect error");
exit(0);
}
printf("pid#%d connected...\n",getpid());
sleep(3);
close(sockfd);
exit(0);
}
}
while(1)
{
cpid = wait(NULL);
if(cpid==-1){
perror("end of wait");
break;
}
printf("pid#%d exit...\n",cpid);
}
return 0;
}
实验结果
服务器端显示：
[email protected]:~/slp/NetWrokProgram/server# ./aworker 2 new connection... new connection... new connection... new connection... new connection...
客户端显示：
[email protected]:~/slp/NetWrokProgram/client# ./a.out pid#16697 connected... pid#16699 connected... pid#16698 connected... pid#16697 exit... pid#16699 exit... pid#16698 exit... pid#16700 connected... pid#16701 connected... pid#16700 exit... pid#16701 exit... connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out connect error: Connection timed out pid#16702 exit... pid#16703 exit... pid#16704 exit... pid#16705 exit... pid#16706 exit... pid#16707 exit... pid#16708 exit... pid#16709 exit... pid#16710 exit... pid#16711 exit... pid#16712 exit... pid#16713 exit... pid#16714 exit... pid#16715 exit... pid#16716 exit... end of wait: No child processes
结果分析：
同时建立连接的客户端进程共有20个，可是只有5个完成了连接的建立，其他15个没有成功。有趣的是，建立的5个链接中有3个是马上建立的，2个是过了一段时间后后来才建立的。
实例分析2
将server端的代码中的sleep(60)注释，即服务端listen即开始进入while循环中的accept阻塞：
...
listen(listenfd,queuelen);
sleep(60); //将这个注释，会出现另一种情况哟~~
while(1)
{
connfd = accept(listenfd,NULL,0);
....
同样的运行服务端结果如下：
[email protected]:~/slp/NetWrokProgram/server# ./aworker 2 new connection... new connection... new connection... new connection... new connection... new connection... new connection... new connection... new connection... new connection... new connection... new connection...
客户端
[email protected]:~/slp/NetWrokProgram/client# ./a.out pid#16736 connected... pid#16737 connected... pid#16738 connected... pid#16739 connected... pid#16740 connected... pid#16741 connected... pid#16742 connected... pid#16743 connected... pid#16744 connected... pid#16745 connected... pid#16746 connected... pid#16747 connected... pid#16748 connected... pid#16749 connected... pid#16750 connected... pid#16751 connected... pid#16752 connected... pid#16753 connected... pid#16755 connected... pid#16754 connected... pid#16736 exit... pid#16737 exit... pid#16738 exit... pid#16739 exit... pid#16740 exit... pid#16741 exit... pid#16742 exit... pid#16743 exit... pid#16744 exit... pid#16745 exit... pid#16746 exit... pid#16747 exit... pid#16748 exit... pid#16749 exit... pid#16750 exit... pid#16751 exit... pid#16752 exit... pid#16753 exit... pid#16755 exit... pid#16754 exit... end of wait: No child processes
结果分析：
由于每个连接在建立之后，已完成队列中的连接马上就被accept给读取了，所以已完成和未完成队列中的连接数之和根本不可能超过backlog限定的个数。
转自：http://blog.csdn.net/ordeder/article/details/21551567
时间： 2024-08-29 09:38:19