基于多进程的网络聊天程序

參考：linux高性能server编程。作者：游双

程序简单介绍：该程序用了共享内存来实现进程间的同步，因为仅仅是同一时候读取共享内存。所以没实用到锁。该程序的功能是server监听网络连接，当有一个client连接时，server创建一个子进程处理该连接。

每一个子进程仅仅负责自己的client以及和父进程通信。当子进程从client读取数据后，把数据放到共享内存上，每一个子进程在共享内存上有自己的一段空间。因此不会出现同一时候写。

放上去后通知父进程，说：共享内存上有新数据到达了，然后父进程通知其它子进程，去到该位置读取数据，把数据发送到自己的client。实现了群聊的效果。该程序对于多进程编程的刚開始学习的人是个不错的样例，写下来是为了让自己熟悉一下。

server代码：编译的时候须要加上 -lrt选项

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>

#define USER_LIMIT 5
#define BUFFER_SIZE 1024
#define FD_LIMIT 65535
#define MAX_EVENT_NUMBER 1024
#define PROCESS_LIMIT 65536

/* 处理一个客户端连接的必要数据 */
struct client_data			
{
	sockaddr_in address;
	int connfd;				/* 客户端的fd  */
	pid_t pid;				/* 处理这个连接的子进程的pid */
	int pipefd[2];			/* 和父进程通信用的管道 */
};

int sig_pipefd[2];//当有信号发生时。用于父进程自己的通信
char* share_mem;
int user_count = 0; //当前客户的数量
client_data* users = 0 ; 
int* sub_process = 0;
static const char* shm_name = "/my_share_memory";
int maxevents = 100;
bool stop_child = false;

void setnonblock(int fd)
{
	int flag = fcntl(fd,F_GETFL);
	assert(flag != -1);
	fcntl(fd,F_SETFL,flag | O_NONBLOCK);
}
void addfd(int epollfd,int fd)
{
	epoll_event ee;
	ee.data.fd = fd;
	ee.events = EPOLLIN | EPOLLET;
	epoll_ctl(epollfd,EPOLL_CTL_ADD,fd,&ee);
	setnonblock(fd);
}
void sig_handler(int sig)
{
	int save_errno = errno;
	int msg = sig;
	send(sig_pipefd[1],(char*)&msg,1,0);
	errno = save_errno;//恢复错误值
}
void child_sig_handler(int sig)
{
	stop_child = true;
}
void addsig(int sig,void (*handler)(int),bool restart = true)
{
	struct sigaction sa;
	memset(&sa,'',sizeof(sa));
	sa.sa_handler = handler;
	if(restart)sa.sa_flags |= SA_RESTART;
	sigfillset(&sa.sa_mask);//作用?
	assert(sigaction(sig,&sa,NULL) != -1);
}
/* 子进程的处理函数。idx表示该子进程处理的客户端连接的编号，users表示全部客户端连接数据的数组，share_mem表示共享内存的起始地址 */
int run_child(int idx,client_data* users,char* share_mem)
{
	int connfd = users[idx].connfd;
	int pipefd = users[idx].pipefd[1];
	int epollfd = epoll_create(100);//子进程的事件处理函数
	assert(epollfd != -1);
	addfd(epollfd,connfd);//与客户端通信
	addfd(epollfd,pipefd);//与父进程通信
	addsig(SIGTERM,child_sig_handler,false);
	epoll_event events[maxevents];

	int ret;
	while(!stop_child)
	{
		int number = epoll_wait(epollfd,events,maxevents,-1);
		if(number < 0 && errno != EINTR)
		{
			printf("epoll error
");
			break;
		}
		int i;
		for(i = 0;i < number;i++)
		{
			int sockfd = events[i].data.fd;
			if(sockfd == connfd && (events[i].events & EPOLLIN))//客户端发来数据
			{
				memset(share_mem+idx*BUFFER_SIZE,'',BUFFER_SIZE);
				/* 将客户端数据读取到相应的读缓存中。该读缓存是共享内存的一段 */
				ret = recv(sockfd,share_mem+idx*BUFFER_SIZE,BUFFER_SIZE-1,0);
				if(ret < 0 && errno != EAGAIN)
				{
					printf("recv error
");
					stop_child =  true;
				}
				else if(ret == 0)
				{
					printf("client close
");
					stop_child = true;
				}
				else 
				{
					send(pipefd,(char*)&idx,sizeof(idx),0);//告诉父进程，“我”收到数据了
				}
			}
			/* 父进程通知"我"将第client个客户端的数据发送到我负责的客户端 */
			else if(sockfd == pipefd && (events[i].events & EPOLLIN))
			{
				int client = 0;
				ret = recv(sockfd,(char*)&client,sizeof(client),0);
				if(ret < 0 && errno != EAGAIN)stop_child = true;
				else if(ret == 0) stop_child = true;
				else
				{
					send(connfd,share_mem+client*BUFFER_SIZE,BUFFER_SIZE,0);
				}
			}
		}
	}
	close(connfd);
	close(pipefd);
	close(epollfd);
	return 0;
}
int main(int argc,char* argv[])
{
	if(argc != 3)
	{
		printf("usage %s server_ip server_port 
",basename(argv[0]));
		return -1;
	}
	sockaddr_in server;
	server.sin_family = AF_INET;
	inet_pton(AF_INET,argv[1],&server.sin_addr);
	server.sin_port = htons(atoi(argv[2]));
	int listenfd = socket(AF_INET,SOCK_STREAM,0);
	assert(listenfd != -1);
	int opt = 1;
	int ret = setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
	assert(ret == 0);
	ret = bind(listenfd,(const sockaddr*)&server,sizeof(server));
	assert(ret != -1);
	ret = listen(listenfd,100);
	assert(ret != -1);

	/* 初始化连接池 */
	user_count = 0;
	users = new client_data[USER_LIMIT+1];
	sub_process = new int[PROCESS_LIMIT];
	int i;
	for(i = 0; i < PROCESS_LIMIT;++i)
	{
		sub_process[i] = -1;
	}

	/* epoll的初始化 */
	int epollfd = epoll_create(100);
	assert(epollfd != -1);
	addfd(epollfd,listenfd);//监听网络连接port

	ret = socketpair(AF_UNIX,SOCK_STREAM,0,sig_pipefd);//当有信号发生时，用于父进程自己的通信
	assert(ret != -1);
	setnonblock(sig_pipefd[1]);//UNIX域套接字的0号port用于信号处理函数
	addfd(epollfd,sig_pipefd[0]);//主进程监听UNIX域套接字的1号port

	/*  设置信号处理函数 */ 
	addsig(SIGCHLD,sig_handler);
	addsig(SIGPIPE,SIG_IGN);
	addsig(SIGINT,sig_handler);
	addsig(SIGTERM,sig_handler);

	/* 创建共享内存，用于全部客户socket连接的读缓存 */
	int shmfd = shm_open(shm_name,O_CREAT|O_RDWR,0666);
	assert(shmfd != -1);
	ret = ftruncate(shmfd,USER_LIMIT*BUFFER_SIZE);//设置shmfd的大小
	assert(ret != -1);
	share_mem = (char*)mmap(NULL,USER_LIMIT*BUFFER_SIZE,PROT_READ|PROT_WRITE,MAP_SHARED,shmfd,0);
	assert(share_mem != MAP_FAILED);
	close(shmfd);

	/* 进入epoll事件循环 */
	bool stop_server = false;
	bool terminate  = false;
	epoll_event events[maxevents];
	while(!stop_server)
	{
		int number = epoll_wait(epollfd,events,maxevents,-1);
		if(number < 0 && errno != EINTR)
		{
			printf("epoll error
");
			break;
		}
		for(i = 0;i < number;i++)
		{
			int sockfd = events[i].data.fd;
			/* 新的客户连接 */
			if(sockfd == listenfd)
			{
				sockaddr_in client;
				socklen_t clilen = sizeof(client);
				int connfd =  accept(listenfd,(struct sockaddr*)&client,&clilen);
				if(connfd < 0)
				{
					printf("accept error
");
					continue;
				}
				if(user_count >= USER_LIMIT)
				{
					const char* info = "to many users
";
					printf("%s
",info);
					send(connfd,info,strlen(info),0);
					close(connfd);
					continue;
				}

				/* 保存第user_count 个客户连接的相关数据  */
				users[user_count].address = client;
				users[user_count].connfd = connfd;
				ret = socketpair(AF_UNIX,SOCK_STREAM,0,users[user_count].pipefd);
				assert( ret != -1);

				pid_t pid = fork();
				if(pid < 0)
				{
					close(connfd);
					continue;
				}
				if(pid == 0)//子进程
				{
					close(sig_pipefd[0]);
					close(sig_pipefd[1]);
					close(users[user_count].pipefd[0]);//子进程关闭0port
					close(listenfd);
					close(epollfd);
					run_child(user_count,users,share_mem);//子进程的处理函数
					munmap((void*)share_mem,USER_LIMIT*BUFFER_SIZE);
					exit(0);
				}
				else //父进程
				{
					close(users[user_count].pipefd[1]);//父进程关闭1port
					close(connfd);
					addfd(epollfd,users[user_count].pipefd[0]);
					users[user_count].pid = pid;
					sub_process[pid] = user_count;
					user_count ++;
				}
			}
			/* 处理信号事件 */
			else if(sockfd ==sig_pipefd[0] &&  events[i].events & EPOLLIN)
			{
				int sig;
				char signals[1024];
				ret = recv(sockfd,signals,sizeof(signals),0);
				if(ret < 0 && ret != EAGAIN)
				{
					printf("recv error
");
					continue;
				}
				if(ret == 0)continue;
				for(i = 0; i < ret; ++ i)
				{
					switch(signals[i])
					{
						case SIGCHLD : //子进程关闭
						{
							pid_t pid;
							int status;
							while((pid = waitpid(-1,&status,WNOHANG)) > 0)
							{
								/* 用子进程的pid获取被关闭的客户端连接的编号 */
								int del_user = sub_process[pid];
								sub_process[del_user] = -1;
								/* 清楚第del_user个客户连接使用的相关数据 */
								epoll_ctl(epollfd,EPOLL_CTL_DEL,users[del_user].pipefd[0],0);
								close(users[del_user].pipefd[0]);
								/* 把最后一个客户连接的信息移动到该位置，用于保证0~user_count-1直接的连接都是活着的 */
								users[del_user] = users[--user_count];
								sub_process[users[del_user].pid] = del_user;
							}
							if(terminate && user_count == 0) stop_server = true;
							break;
						}
						case SIGINT :
						case SIGTERM : //结束服务器进程
						{
							printf("kill all the child now
");
							for(i = 0 ;i < user_count;++i)
							{
								pid_t pid = users[i].pid;
								kill(pid,SIGTERM);
							}
							terminate = true;//此处不是stop_sever是为了等待全部子进程结束后再结束
							break;
						}
						default : break;
					}
				}
			}
			/* 某个子进程向父进程写入了数据 */
			else if(events[i].events & EPOLLIN)
			{
				int child;
				ret = recv(sockfd,(char*)&child,sizeof(child),0);
				if(ret < 0 && errno != EAGAIN) continue;
				else if(ret == 0)continue;
				printf("read data from child accross pipe
");
				for(i = 0 ;i < user_count;i++)
				{
					if(i != child)
					{
						printf("send data to child accross pipe
");
						send(users[i].pipefd[0],(char*)&child,sizeof(child),0);
					}
				}
			}
		}
	}
	close(listenfd);
	close(epollfd);
	close(sig_pipefd[0]);
	close(sig_pipefd[1]);
	shm_unlink(shm_name);
	delete[] users;
	delete[] sub_process;
	return 0;
}

client代码(比較简单。就没有给出凝视)：

#define _GNU_SOURCE 1
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <poll.h>
#include <fcntl.h>

#define BUFFER_SIZE 64

int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number
", basename( argv[0] ) );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );

    struct sockaddr_in server_address;
    bzero( &server_address, sizeof( server_address ) );
    server_address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &server_address.sin_addr );
    server_address.sin_port = htons( port );

    int sockfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( sockfd >= 0 );
    if ( connect( sockfd, ( struct sockaddr* )&server_address, sizeof( server_address ) ) < 0 )
    {
        printf( "connection failed
" );
        close( sockfd );
        return 1;
    }

    pollfd fds[2];
    fds[0].fd = 0;
    fds[0].events = POLLIN;
    fds[0].revents = 0;
    fds[1].fd = sockfd;
    fds[1].events = POLLIN | POLLRDHUP;
    fds[1].revents = 0;
    char read_buf[BUFFER_SIZE];
    int pipefd[2];
    int ret = pipe( pipefd );
    assert( ret != -1 );

    while( 1 )
    {
        ret = poll( fds, 2, -1 );
        if( ret < 0 )
        {
            printf( "poll failure
" );
            break;
        }

        if( fds[1].revents & POLLRDHUP )
        {
            printf( "server close the connection
" );
            break;
        }
        else if( fds[1].revents & POLLIN )
        {
            memset( read_buf, '', BUFFER_SIZE );
            int len = recv( fds[1].fd, read_buf, BUFFER_SIZE-1, 0 );
			int i;
		    for(i = 0;i<len;i++)printf("%c",read_buf[i]);
        }

        if( fds[0].revents & POLLIN )
        {
            ret = splice( 0, NULL, pipefd[1], NULL, 32768, SPLICE_F_MORE | SPLICE_F_MOVE );
            ret = splice( pipefd[0], NULL, sockfd, NULL, 32768, SPLICE_F_MORE | SPLICE_F_MOVE );
        }
    }
    
    close( sockfd );
    return 0;
}