Linux网络编程--使用epoll,共享内存技术实现高性能的聊天室程序

#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

struct client_data
{
sockaddr_in address;
int connfd;
pid_t pid;
int pipefd[2];
};

static const char* shm_name = "/my_shm";
int sig_pipefd[2];
int epollfd;
int listenfd;
int shmfd;
char* share_mem = 0;
client_data* users = 0;
int* sub_process = 0;
int user_count = 0;
bool stop_child = false;

int setnonblocking( int fd )
{
int old_option = fcntl( fd, F_GETFL );
int new_option = old_option | O_NONBLOCK;
//将fd设置为非阻塞
fcntl( fd, F_SETFL, new_option );
return old_option;
}

void addfd( int epollfd, int fd )
{
epoll_event event;
event.data.fd = fd;
event.events = EPOLLIN | EPOLLET;
epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );
//注册fd到epollfd监听队列中
setnonblocking( fd );
}

void sig_handler( int sig )
{
int save_errno = errno;
int msg = sig;
send( sig_pipefd[1], ( char* )&msg, 1, 0 );
//发送信号的值到管道的写端
errno = save_errno;
}

void addsig( int sig, void(*handler)(int), bool restart = true )
{
struct sigaction sa;
memset( &sa, '\0', sizeof( sa ) );
sa.sa_handler = handler;
if( restart )
{
sa.sa_flags |= SA_RESTART;
//如果由于此信号影响程序运行，加上SA_RESTART标志使程序重新启动
}
sigfillset( &sa.sa_mask );
//初始化所以信号
assert( sigaction( sig, &sa, NULL ) != -1 );
//使用sigaction设置信号发生器
}

void del_resource()
{
close( sig_pipefd[0] );
close( sig_pipefd[1] );
close( listenfd );
close( epollfd );
shm_unlink( shm_name );
//删除/关闭共享内存
delete [] users;
delete [] sub_process;
}

void child_term_handler( int sig )
{
stop_child = true;
}

int run_child( int idx, client_data* users, char* share_mem )
//第idx个用户  用户数据结构     共享内存标识符
{
epoll_event events[ MAX_EVENT_NUMBER ];
int child_epollfd = epoll_create( 5 );
assert( child_epollfd != -1 );
int connfd = users[idx].connfd;
addfd( child_epollfd, connfd );
int pipefd = users[idx].pipefd[1];
addfd( child_epollfd, pipefd );
//监听和父进程通信管道的写端
int ret;
addsig( SIGTERM, child_term_handler, false );

while( !stop_child )
{
int number = epoll_wait( child_epollfd, events, MAX_EVENT_NUMBER, -1 );
if ( ( number < 0 ) && ( errno != EINTR ) )
{
printf( "epoll failure\n" );
break;
}

for ( int i = 0; i < number; i++ )
{
int sockfd = events[i].data.fd;
if( ( sockfd == connfd ) && ( events[i].events & EPOLLIN ) )
//如果是连接描述符，那么就处理本描述符上的读事件
{
memset( share_mem + idx*BUFFER_SIZE, '\0', BUFFER_SIZE );
//初始化用户idx内存区域
ret = recv( connfd, share_mem + idx*BUFFER_SIZE, BUFFER_SIZE-1, 0 );
if( ret < 0 )
{
if( errno != EAGAIN )
{
stop_child = true;
}
}
else if( ret == 0 )
//服务端程序已经关闭，结束子进程
{
stop_child = true;
}
else
//发送数据（客户端序号）给写管道
{
send( pipefd, ( char* )&idx, sizeof( idx ), 0 );
}
}
else if( ( sockfd == pipefd ) && ( events[i].events & EPOLLIN ) )
//如果是管道消息
{
int client = 0;
ret = recv( sockfd, ( char* )&client, sizeof( client ), 0 );
//接收数据（客户端序号）
if( ret < 0 )
{
if( errno != EAGAIN )
{
stop_child = true;
}
}
else if( ret == 0 )
{
stop_child = true;
}
else
{
send( connfd, share_mem + client * BUFFER_SIZE, BUFFER_SIZE, 0 );
}
}
else
{
continue;
}
}
}

close( connfd );
close( pipefd );
close( child_epollfd );
return 0;
}

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

int ret = 0;
struct sockaddr_in address;
bzero( &address, sizeof( address ) );
address.sin_family = AF_INET;
inet_pton( AF_INET, ip, &address.sin_addr );
address.sin_port = htons( port );

listenfd = socket( PF_INET, SOCK_STREAM, 0 );
assert( listenfd >= 0 );

ret = bind( listenfd, ( struct sockaddr* )&address, sizeof( address ) );
assert( ret != -1 );

ret = listen( listenfd, 5 );
assert( ret != -1 );

user_count = 0;
users = new client_data [ USER_LIMIT+1 ];
//创建 USER_LIMIT个 client_data数据结构
sub_process = new int [ PROCESS_LIMIT ];
//创建 PROCESS_LIMIT 个 sub_process int型数组，用于存储进程PID，用来索引用户数据结构
for( int i = 0; i < PROCESS_LIMIT; ++i )
{
sub_process[i] = -1;
}

epoll_event events[ MAX_EVENT_NUMBER ];
epollfd = epoll_create( 5 );
assert( epollfd != -1 );
addfd( epollfd, listenfd );
//监听listenfd描述符

ret = socketpair( PF_UNIX, SOCK_STREAM, 0, sig_pipefd );
assert( ret != -1 );
setnonblocking( sig_pipefd[1] );
addfd( epollfd, sig_pipefd[0] );
//监听sig_pipefd[0]读描述符（监听信号事件）

addsig( SIGCHLD, sig_handler );
addsig( SIGTERM, sig_handler );
addsig( SIGINT, sig_handler );
addsig( SIGPIPE, SIG_IGN );
//注册信号发生器
bool stop_server = false;
bool terminate = false;

shmfd = shm_open( shm_name, O_CREAT | O_RDWR, 0666 );
//posix共享内存的创建/打开
assert( shmfd != -1 );
ret = ftruncate( shmfd, USER_LIMIT * BUFFER_SIZE );
//清空内存区域
assert( ret != -1 );

share_mem = (char*)mmap( NULL, USER_LIMIT * BUFFER_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0 );
//映射共享内存的文件描述符到内存区域
assert( share_mem != MAP_FAILED );
close( shmfd );

while( !stop_server )
{
int number = epoll_wait( epollfd, events, MAX_EVENT_NUMBER, -1 );
//使用I/O复用技术等待number个活跃事件的发生,并将事件结果存储在events结构体中
if ( ( number < 0 ) && ( errno != EINTR ) )
{
printf( "epoll failure\n" );
break;
}

for ( int i = 0; i < number; i++ )
{
int sockfd = events[i].data.fd;
if( sockfd == listenfd )
{
struct sockaddr_in client_address;
socklen_t client_addrlength = sizeof( client_address );
int connfd = accept( listenfd, ( struct sockaddr* )&client_address, &client_addrlength );
if ( connfd < 0 )
{
printf( "errno is: %d\n", errno );
continue;
}
if( user_count >= USER_LIMIT )
//如果用户数超过5个就拒绝建立连接
{
const char* info = "too many users\n";
printf( "%s", info );
send( connfd, info, strlen( info ), 0 );
close( connfd );
continue;
}
users[user_count].address = client_address;
users[user_count].connfd = connfd;
//对建立连接的客户进行数据处理
ret = socketpair( PF_UNIX, SOCK_STREAM, 0, users[user_count].pipefd );
//fork之前使用 socketpair建立双向管道，子进程继承此管道
assert( ret != -1 );
pid_t pid = fork();
if( pid < 0 )
//如果fork失败继续fork
{
close( connfd );
continue;
}
else if( pid == 0 )
//子进程一直监听处理本描述符发送的事件
{
close( epollfd );
close( listenfd );
close( users[user_count].pipefd[0] );
close( sig_pipefd[0] );
close( sig_pipefd[1] );
//子进程不处理信号管道事件，所以关闭描述符
run_child( user_count, users, share_mem );
munmap( (void*)share_mem,  USER_LIMIT * BUFFER_SIZE );
//解除内存映射
exit( 0 );
}
else
//父进程
{
close( connfd );
close( users[user_count].pipefd[1] );
//关闭管道的写端，只保留读端
addfd( epollfd, users[user_count].pipefd[0] );
//注册用户的读端事件
users[user_count].pid = pid;
//对用户数据pid赋值
sub_process[pid] = user_count;
//sub_process为了索引哪个进程处理某个客户端
user_count++;
}
}
else if( ( sockfd == sig_pipefd[0] ) && ( events[i].events & EPOLLIN ) )
//信号事件
{
int sig;
char signals[1024];
ret = recv( sig_pipefd[0], signals, sizeof( signals ), 0 );
if( ret == -1 )
{
continue;
}
else if( ret == 0 )
{
continue;
}
else
{
for( int i = 0; i < ret; ++i )
{
switch( signals[i] )
{
case SIGCHLD:
{
pid_t pid;
int stat;
while ( ( pid = waitpid( -1, &stat, WNOHANG ) ) > 0 )
{
int del_user = sub_process[pid];
sub_process[pid] = -1;
if( ( del_user < 0 ) || ( del_user > USER_LIMIT ) )
{
printf( "the deleted user was not change\n" );
continue;
}
epoll_ctl( epollfd, EPOLL_CTL_DEL, users[del_user].pipefd[0], 0 );
close( users[del_user].pipefd[0] );
users[del_user] = users[--user_count];
sub_process[users[del_user].pid] = del_user;
printf( "child %d exit, now we have %d users\n", del_user, user_count );
}
if( terminate && user_count == 0 )
{
stop_server = true;
}
break;
}
case SIGTERM:
case SIGINT:
{
printf( "kill all the clild now\n" );
//addsig( SIGTERM, SIG_IGN );
//addsig( SIGINT, SIG_IGN );
if( user_count == 0 )
{
stop_server = true;
break;
}
for( int i = 0; i < user_count; ++i )
{
int pid = users[i].pid;
kill( pid, SIGTERM );
}
terminate = true;
break;
}
default:
{
break;
}
}
}
}
}
else if( events[i].events & EPOLLIN )
//如果子进程的run_child函数处理完毕，之后会触发这个条件。同时接受客户端的序号
{
int child = 0;
ret = recv( sockfd, ( char* )&child, sizeof( child ), 0 );
printf( "read data from child accross pipe\n" );
if( ret == -1 )
{
continue;
}
else if( ret == 0 )
{
continue;
}
else
//给每个客户端读管道派发数据（客户端序号）
{
for( int j = 0; j < user_count; ++j )
{
if( users[j].pipefd[0] != sockfd )
{
printf( "send data to child accross pipe\n" );
send( users[j].pipefd[0], ( char* )&child, sizeof( child ), 0 );
}
}
}
}
}
}

del_resource();
return 0;
}