Reactor实现原理及代码示例

回顾

上篇文章我们学习了IO相关的知识，今天我们来聊聊基于IO复用模型的Reactor的实现及原理。

一、什么是Reactor

在处理web请求时，通常有两种体系结构，分别是：thread-based architecture（基于线程）和 event-driven architecture（事件驱动）。

1.1 thread-based architecture

基于线程的体系结构，通常使用多线程来处理客户端请求，每当收到一个客户端请求，就创建一个线程处理该请求。这种设计思路很简单，但是有一个致命的缺陷，就是只使用于并发量不大的场景下。因为线程需要占用内存和CPU资源，且操作系统在线程之间切换也有一定的开销，当线程数量达到一定数量后，该web服务可能就“疲于奔命”了。

基于线程的服务端代码示例：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define BUFFER_LENGTH	128

// thread --> fd
void *routine(void *arg) {
	int clientfd = *(int *)arg;
	while (1) {
		unsigned char buffer[BUFFER_LENGTH] = {0};
		int ret = recv(clientfd, buffer, BUFFER_LENGTH, 0);
		if (ret == 0) {
			close(clientfd);
			break;
		}
		printf("buffer : %s, ret: %d\n", buffer, ret);
		ret = send(clientfd, buffer, ret, 0); // 
	}
}

int main() 
{
	// 创建监听fd
	int listenfd = socket(AF_INET, SOCK_STREAM, 0);  // 
	if (listenfd == -1) return -1;
	
	struct sockaddr_in servaddr;
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(9999);
	
	// 绑定
	if (-1 == bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr))) {
		return -2;
	}
	// 设置listenfd为非阻塞模式
	// int flag = fcntl(listenfd, F_GETFL, 0);
	// flag |= O_NONBLOCK;
	// fcntl(listenfd, F_SETFL, flag);

	listen(listenfd, 10); // 默认listenfd为阻塞模式

	while (1) {
		struct sockaddr_in client;
		socklen_t len = sizeof(client);
		// 阻塞等待客户端连接上来
		int clientfd = accept(listenfd, (struct sockaddr*)&client, &len);
		
		pthread_t threadid;
		// 为连接上来的客户端fd，创建线程，并叫该客户端fd作为参数传入，线程处理函数
		pthread_create(&threadid, NULL, routine, &clientfd);
	}

	return 0;
}

1.2 event-driven architecture，事件驱动

事件驱动体系结构是目前使用较为广泛的一种。这种方式会定义一系列事件处理器来响应对应的事件，在服务端做到连接处理和事件处理分离。

Reactor就是event-driven architecture的一种实现方式，处理多个客户端向服务端发送请求的场景。Reactor会解耦并发请求，并分发到对应的时间处理器去处理。目前，许多流行的开源框架都用到了reactor模式，如Redis、netty、nginx等等。

Reactor主要由以下几个角色构成：

• 文件描述符（Linux，在windows环境下叫句柄）：发生在 fd 上的事件可以有：连接、读事件和写事件。
• 同步事件分离器：本质上是系统调用，如：Linux中的select、poll和epoll。
• 初始分发器：当select、poll或epoll 检测到 fd 有事件发生时，会调用特定的回调函数。
• 事件处理器：通常会定义一些回调函数。fd 上有事件发生，执行对应的回调函数。

代码示例

#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 
#include 

#define BUFFER_LENGTH		4096
#define MAX_EPOLL_EVENTS	1024
#define SERVER_PORT			8888
#define PORT_COUNT			1

typedef int NCALLBACK(int ,int, void*);
int recv_cb(int fd, int events, void *arg);
int send_cb(int fd, int events, void *arg);
struct ntyevent *ntyreactor_idx(struct ntyreactor *reactor, int sockfd);

struct ntyevent {
	int fd;
	int events;
	void *arg;
	int (*callback)(int fd, int events, void *arg);
	int status;
	char buffer[BUFFER_LENGTH];
	int length;
	long last_active;
};

struct eventblock {
	struct eventblock *next;
	struct ntyevent *events;
};

struct ntyreactor {
	int epfd;
	int blkcnt;
	struct eventblock *evblk; //fd --> 100w
};

// 初始化ntyevent对象（设置fd，绑定回调，给回调传参等）
void nty_event_set(struct ntyevent *ev, int fd, NCALLBACK callback, void *arg) {
	ev->fd = fd;
	ev->callback = callback;
	ev->events = 0;
	ev->arg = arg;
	ev->last_active = time(NULL);
	return ;	
}


int nty_event_add(int epfd, int events, struct ntyevent *ev) {
	struct epoll_event ep_ev = {0, {0}};
	ep_ev.data.ptr = ev;
	ep_ev.events = ev->events = events;

	int op;
	if (ev->status == 1) {
		op = EPOLL_CTL_MOD;
	} else {
		op = EPOLL_CTL_ADD;
		ev->status = 1;
	}
	if (epoll_ctl(epfd, op, ev->fd, &ep_ev) < 0) {
		printf("event add failed [fd=%d], events[%d]\n", ev->fd, events);
		return -1;
	}
	return 0;
}

// 将ntyevent对象从 epoll集合中删除
int nty_event_del(int epfd, struct ntyevent *ev) {
	struct epoll_event ep_ev = {0, {0}};
	if (ev->status != 1) {
		return -1;
	}
	ep_ev.data.ptr = ev;
	ev->status = 0;
	epoll_ctl(epfd, EPOLL_CTL_DEL, ev->fd, &ep_ev);
	return 0;
}

int recv_cb(int fd, int events, void *arg) {

	struct ntyreactor *reactor = (struct ntyreactor*)arg;
	struct ntyevent *ev = ntyreactor_idx(reactor, fd);

	int len = recv(fd, ev->buffer, BUFFER_LENGTH , 0); // 
	nty_event_del(reactor->epfd, ev);   // 删除该对象的读事件

	if (len > 0) {
		ev->length = len;
		ev->buffer[len] = '\0';
		printf("C[%d]:%s\n", fd, ev->buffer)
		nty_event_set(ev, fd, send_cb, reactor);
		nty_event_add(reactor->epfd, EPOLLOUT, ev);  // 加入该对象的写事件
	} else if (len == 0) {
		close(ev->fd);
		//printf("[fd=%d] pos[%ld], closed\n", fd, ev-reactor->events);
	} else {
		close(ev->fd);
		printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno));
	}
	return len;
}

int send_cb(int fd, int events, void *arg) {
	struct ntyreactor *reactor = (struct ntyreactor*)arg;
	struct ntyevent *ev = ntyreactor_idx(reactor, fd);

	// 填充完数据返回给客户端
	int len = send(fd, ev->buffer, ev->length, 0);
	if (len > 0) {
		printf("send[fd=%d], [%d]%s\n", fd, len, ev->buffer);

		nty_event_del(reactor->epfd, ev);     // 删除写事件
		nty_event_set(ev, fd, recv_cb, reactor);
		nty_event_add(reactor->epfd, EPOLLIN, ev);  // 加入读事件
		
	} else {
		close(ev->fd);
		nty_event_del(reactor->epfd, ev);
		printf("send[fd=%d] error %s\n", fd, strerror(errno));
	}
	return len;
}

// 将连接上来的client fd，创建ntyevent对象，并绑定recv_cb，加入到epoll集合
int accept_cb(int fd, int events, void *arg) {
	struct ntyreactor *reactor = (struct ntyreactor*)arg;
	if (reactor == NULL) return -1;

	struct sockaddr_in client_addr;
	socklen_t len = sizeof(client_addr);

	int clientfd;
	if ((clientfd = accept(fd, (struct sockaddr*)&client_addr, &len)) == -1) {
		if (errno != EAGAIN && errno != EINTR) {
			
		}
		printf("accept: %s\n", strerror(errno));
		return -1;
	}
	// int flag = 0;
	// if ((flag = fcntl(clientfd, F_SETFL, O_NONBLOCK)) < 0) {
	// 	printf("%s: fcntl nonblocking failed, %d\n", __func__, MAX_EPOLL_EVENTS);
	// 	return -1;
	// }
	struct ntyevent *event = ntyreactor_idx(reactor, clientfd);
	nty_event_set(event, clientfd, recv_cb, reactor);
	nty_event_add(reactor->epfd, EPOLLIN, event);
	printf("new connect [%s:%d], pos[%d]\n", 
		inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), clientfd);
	return 0;
}

int init_sock(short port) {

	int fd = socket(AF_INET, SOCK_STREAM, 0);
	fcntl(fd, F_SETFL, O_NONBLOCK);

	struct sockaddr_in server_addr;
	memset(&server_addr, 0, sizeof(server_addr));
	server_addr.sin_family = AF_INET;
	server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	server_addr.sin_port = htons(port);

	bind(fd, (struct sockaddr*)&server_addr, sizeof(server_addr));

	if (listen(fd, 20) < 0) {
		printf("listen failed : %s\n", strerror(errno));
	}

	return fd;
}


int ntyreactor_alloc(struct ntyreactor *reactor) {

	if (reactor == NULL) return -1;
	if (reactor->evblk == NULL) return -1;

	struct eventblock *blk = reactor->evblk;
	while (blk->next != NULL) {
		blk = blk->next;
	}

	struct ntyevent *evs = (struct ntyevent*)malloc((MAX_EPOLL_EVENTS) * sizeof(struct ntyevent));
	if (evs == NULL) {
		printf("ntyreactor_alloc ntyevents failed\n");
		return -2;
	}
	memset(evs, 0, (MAX_EPOLL_EVENTS) * sizeof(struct ntyevent));

	struct eventblock *block = (struct eventblock *)malloc(sizeof(struct eventblock));
	if (block == NULL) {
		printf("ntyreactor_alloc eventblock failed\n");
		return -2;
	}
	memset(block, 0, sizeof(struct eventblock));

	block->events = evs;
	block->next = NULL;

	blk->next = block;
	reactor->blkcnt ++; //

	return 0;
}

struct ntyevent *ntyreactor_idx(struct ntyreactor *reactor, int sockfd) {
	int blkidx = sockfd / MAX_EPOLL_EVENTS;
	while (blkidx >= reactor->blkcnt) {
		ntyreactor_alloc(reactor);
	}
	struct eventblock *blk = reactor->evblk;

	int i = 0;
	while(i ++ < blkidx && blk != NULL) {
		blk = blk->next;
	}
	return &blk->events[sockfd % MAX_EPOLL_EVENTS];
}


int ntyreactor_init(struct ntyreactor *reactor) {
	if (reactor == NULL) return -1;
	memset(reactor, 0, sizeof(struct ntyreactor));

	// 1. 创建epoll fd
	reactor->epfd = epoll_create(1);
	if (reactor->epfd <= 0) {
		printf("create epfd in %s err %s\n", __func__, strerror(errno));
		return -2;
	}

	// 2.创建一个event对象
	struct ntyevent *evs = (struct ntyevent*)malloc((MAX_EPOLL_EVENTS) * sizeof(struct ntyevent));
	if (evs == NULL) {
		printf("ntyreactor_alloc ntyevents failed\n");
		return -2;
	}
	memset(evs, 0, (MAX_EPOLL_EVENTS) * sizeof(struct ntyevent));

	// 3.初始化链表第一个block
	struct eventblock *block = (struct eventblock *)malloc(sizeof(struct eventblock));
	if (block == NULL) {
		printf("ntyreactor_alloc eventblock failed\n");
		return -2;
	}
	memset(block, 0, sizeof(struct eventblock));

	block->events = evs;
	block->next = NULL;

	reactor->evblk = block;
	reactor->blkcnt = 1;

	return 0;
}

int ntyreactor_destory(struct ntyreactor *reactor) {

	close(reactor->epfd);
	//free(reactor->events);

	struct eventblock *blk = reactor->evblk;
	struct eventblock *blk_next = NULL;

	while (blk != NULL) {
		blk_next = blk->next;
		free(blk->events);
		free(blk);
		blk = blk_next;
	}
	return 0;
}


// 将多个服务器socket，加入到epoll集合，
int ntyreactor_addlistener(struct ntyreactor *reactor, int sockfd, NCALLBACK *acceptor) {
	if (reactor == NULL) return -1;
	if (reactor->evblk == NULL) return -1;

	//reactor->evblk->events[sockfd];
	struct ntyevent *event = ntyreactor_idx(reactor, sockfd);

	nty_event_set(event, sockfd, acceptor, reactor);

	nty_event_add(reactor->epfd, EPOLLIN, event);
	return 0;
}

int ntyreactor_run(struct ntyreactor *reactor) {
	if (reactor == NULL) return -1;
	if (reactor->epfd < 0) return -1;
	if (reactor->evblk == NULL) return -1;
	struct epoll_event events[MAX_EPOLL_EVENTS+1];
	
	int checkpos = 0, i;

	while (1) {

		int nready = epoll_wait(reactor->epfd, events, MAX_EPOLL_EVENTS, -1);
		if (nready < 0) {
			printf("epoll_wait error, exit\n");
			continue;
		}

		for (i = 0;i < nready;i ++) {
			struct ntyevent *ev = (struct ntyevent*)events[i].data.ptr;
			printf("current ready fd = %d\n", ev->fd);
			
			//   回调函数在这里被调用
			if ((events[i].events & EPOLLIN) && (ev->events & EPOLLIN)) {
				ev->callback(ev->fd, events[i].events, ev->arg);
			}
			if ((events[i].events & EPOLLOUT) && (ev->events & EPOLLOUT)) {
				ev->callback(ev->fd, events[i].events, ev->arg);
			}	
		}
	}
}

// 3, 6w, 1, 100 == 
// 

int main(int argc, char *argv[]) {
	unsigned short port = SERVER_PORT; // listen 8888
	if (argc == 2) {
		port = atoi(argv[1]);
	}
	struct ntyreactor *reactor = (struct ntyreactor*)malloc(sizeof(struct ntyreactor));
	ntyreactor_init(reactor);

	int i = 0;
	int sockfds[PORT_COUNT] = {0};
	for (i = 0;i < PORT_COUNT;i ++) {
		sockfds[i] = init_sock(port+i);
		printf("listen fd = %d\n", sockfds[i]);
		ntyreactor_addlistener(reactor, sockfds[i], accept_cb);
	}

	ntyreactor_run(reactor);
	ntyreactor_destory(reactor);

	for (i = 0;i < PORT_COUNT;i ++) {
		close(sockfds[i]);
	}
	free(reactor);

	return 0;
}

文章参考于<零声教育>的C/C++linux服务期高级架构。