c/c++后台开发学习笔记 2.1.2 reactor原理与实现，实现百万级并发

reactor

把epoll返回的fd读写事件进行封装，并为每种事件设置回调函数，把所有关注的fd以及对应的事件存储在一个数据结构里，与epoll内部的红黑树的节点形成一一对应的关系。epoll返回时使用data.ptr得到我们数据结构中对应的entry，再进行处理

对fd的封装如下

typedef int (*NCALLBACK)(int fd, int events, void *arg);

struct ntyevent {
	int fd;
	int events;                     //监听的事件：EPOLLIN或EPOLLOUT
	void *arg;                      //传给回调函数的额外参数（reactor指针）
	NCALLBACK callback;             //回调函数
	
	int used;                       //当前entry是有有效
	char buffer[BUFFER_LENGTH];     //读写共用一个buffer，因为当前监听的事件只能是读或写，不会两个都有
	int length;                     //buffer中有效数据的长度
	long last_active;               //当前fd上一次活跃的事件
	int sticky;                     //如果置为1，则fd不会因为长时间不活跃而被关闭（用于listenfd）
};

reactor数据结构的定义如下

struct ntyreactor {
	int epfd;
	int block_num;
	struct ntyevent **events; //array of ntyevent *, length = block_num, each block has 1024 ntyevent
};

events是一个指针数组，可扩容。每个元素指向一个1024长度的ntyevent数组

整个服务器大致有如下函数

int accept_cb(int fd, int events, void *arg);
int recv_cb(int fd, int events, void *arg);
int send_cb(int fd, int events, void *arg);

void nty_event_update(struct ntyevent *ev, int fd, NCALLBACK callback, void *arg);
int nty_event_add(int epfd, int events, struct ntyevent *ev);
int nty_event_del(int epfd, struct ntyevent *ev);

int start_listen(short port);
int ntyreactor_init(struct ntyreactor *reactor);
struct ntyevent *ntyreactor_get_event(struct ntyreactor *reactor, int fd);
int ntyreactor_destory(struct ntyreactor *reactor);
int ntyreactor_addlistener(struct ntyreactor *reactor, int listenfd, NCALLBACK acceptor);
int ntyreactor_run(struct ntyreactor *reactor);

先看main函数

#define BUFFER_LENGTH		4096
#define EVENTS_BLOCK_SIZE	1024
#define EVENT_BATCH_SIZE    1024
#define SERVER_PORT			8888
#define PORT_COUNT          100
#define CLIENT_TIMEOUT      15

int main(int argc, char *argv[]) {

	unsigned short port = SERVER_PORT;
	if (argc == 2) {
		port = atoi(argv[1]);
	}

	struct ntyreactor *reactor = (struct ntyreactor*)calloc(1, sizeof(struct ntyreactor));
	ntyreactor_init(reactor);
	
	int i;
	for(i = 0; i < PORT_COUNT; i++) {
		int listenfd = start_listen(port + i);
		ntyreactor_addlistener(reactor, listenfd, accept_cb);
	}
	ntyreactor_run(reactor);

	ntyreactor_destory(reactor);
	free(reactor);
	return 0;
}

PORT_COUNT设为100时，程序监听从8888开始的100个端口，每个端口至少能接受1万个port，所以连接数能达到一百万。（因为测试的客户端数量比较少，如果不多监听一些端口，会导致（src-ip, src-port, dst-ip, dst-port) 四元组的数量不够用）

其中

ntyreactor_run

是程序主循环

int ntyreactor_run(struct ntyreactor *reactor) {
	if (reactor == NULL) return -1;
	if (reactor->epfd < 0) return -1;
	if (reactor->events == NULL) return -1;
	
	struct epoll_event events[EVENT_BATCH_SIZE];
	
	int block_idx = 0, check_interval = 10, i, cur; // check every 10 loops

	while (1) {
#if CHECK_TIMEOUT
		cur++;
		if (cur % check_interval == 9) {
			if (block_idx >= reactor->block_num) {
				block_idx = 0;
			}
			ntyreactor_check_timeout(reactor, block_idx++);
		}
#endif
		int nready = epoll_wait(reactor->epfd, events, EVENT_BATCH_SIZE, 1000);
		if (nready < 0) {
			printf("epoll_wait error\n");
			continue;
		}

		for (i = 0; i < nready; i++) {

			struct ntyevent *ev = (struct ntyevent*)events[i].data.ptr;
			int err = 0;
			if ((events[i].events & EPOLLIN) && (ev->events & EPOLLIN)) {
				err = ev->callback(ev->fd, events[i].events, ev->arg);
			}
			if ((events[i].events & EPOLLOUT) && (ev->events & EPOLLOUT)) {
				err = ev->callback(ev->fd, events[i].events, ev->arg);
			}
			
		}

	}
}

主循环中对于每个监听到的事件直接调用回调函数

accept_cb把每个新连接添加到epoll和reactor中监控

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 i = 0;
	struct ntyevent *event = ntyreactor_get_event(reactor, clientfd);
	if (event == NULL) return -1;

	do {

		// 设置clientfd非阻塞
		if (fcntl(clientfd, F_SETFL, O_NONBLOCK) < 0) {
			printf("%s: fcntl nonblocking failed, %d\n", __func__, EVENTS_BLOCK_SIZE);
			break;
		}

		nty_event_update(event, clientfd, recv_cb, reactor);
		nty_event_add(reactor->epfd, EPOLLIN, event);

	} while (0);

	printf("new connect [%s:%d][time:%ld], pos[%d]\n", 
		inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), event->last_active, i);

	return 0;

}

recv_cb 和 send_cb分别负责读和写

这里要提到水平触发和边沿触发的问题

水平触发是只要条件为真就一直触发（例如只要buffer里数据还没读完，epoll就一直触发EPOLLIN），而边沿触发只在条件从假变为真时触发一次

通常，数据量较大时使用水平触发（一次读不完buffer当中所有数据时）。数据较小是可以使用边沿触发。边沿触发每次必须用while循环读取所有数据。

这段代码使用的是水平触发。

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

	struct ntyreactor *reactor = (struct ntyreactor*)arg;
	struct ntyevent *ev =  ntyreactor_get_event(reactor, fd);
	if(ev == NULL) return -1;

	int len = recv(fd, ev->buffer, BUFFER_LENGTH, 0);
	nty_event_del(reactor->epfd, ev);

	if (len > 0) {
		ev->length = len;
		ev->buffer[len] = '\0';
		printf("C[%d]:%s\n", fd, ev->buffer);

		nty_event_update(ev, fd, send_cb, reactor);
		nty_event_add(reactor->epfd, EPOLLOUT, ev);
	} else if (len == 0) {
		close(ev->fd);
		printf("[fd=%d] closed\n", fd);
	} 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_get_event(reactor, fd);
	if(ev == NULL) return -1;

	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);
		nty_event_update(ev, fd, recv_cb, reactor);
		nty_event_add(reactor->epfd, EPOLLIN, ev);
		
	} else {

		close(ev->fd);

		nty_event_del(reactor->epfd, ev);
		printf("send[fd=%d] error %s\n", fd, strerror(errno));

	}

	return len;
}

reactor自动扩容通过ntyreactor_get_event实现

//输入fd，返回对应的ntyevent
struct ntyevent *ntyreactor_get_event(struct ntyreactor *reactor, int fd) {
	int b = fd / EVENTS_BLOCK_SIZE;
	int i = fd % EVENTS_BLOCK_SIZE;
	if(b >= reactor->block_num) {
		int new_block_num = reactor->block_num == 0 ? 1 : 2 * reactor->block_num;
		while(new_block_num <= b) new_block_num <<= 1;
		struct ntyevent **new_event_blocks = (struct ntyevent **)realloc(
			reactor->events, new_block_num * (sizeof(struct ntyevent *))
		);
		if(new_event_blocks == NULL) {
			printf("cannot allocate block in %s for fd = %d\n", __func__, fd);
			return NULL;
		}
		memset(
			new_event_blocks + reactor->block_num, 0,
			(new_block_num - reactor->block_num) * sizeof(struct ntyevent*));
		reactor->block_num = new_block_num;
		reactor->events = new_event_blocks;
	}
	
	if(reactor->events[b] == NULL) {
		reactor->events[b] = (struct ntyevent *)calloc(EVENTS_BLOCK_SIZE, sizeof(struct ntyevent));
		if (reactor->events[b] == NULL) {
			printf("cannot allocate block in %s for fd = %d\n", __func__, fd);
			return NULL;
		}
	}

	return &reactor->events[b][i];
}

使用 ntyreactor_check_timeout自动检查block_idx中长时间不活跃的fd并关闭连接

int ntyreactor_check_timeout(struct ntyreactor *reactor, int block_idx) {
	if(!reactor || !reactor->events || block_idx >= reactor->block_num) return 0;
	struct ntyevent *block = reactor->events[block_idx];
	if (!block) return 0;

	long now = time(NULL);
	int i;
	for(i = 0; i < EVENTS_BLOCK_SIZE; i++) {
		if(!block[i].used || block[i].sticky) continue;
		long duration = now - block[i].last_active;
		if (duration >= 60) {
			close(block[i].fd);
			printf("[fd=%d] timeout\n", block[i].fd);
			nty_event_del(reactor->epfd, &block[i]);
		}
	}
}

nty_event_* 这几个函数负责把fd和监听的event加入到epoll和reactor中，并设置回调函数

void nty_event_update(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);
	ev->sticky = 0;
}

// add/update ev on epfd with events
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->used == 1) {
		op = EPOLL_CTL_MOD;
	} else {
		op = EPOLL_CTL_ADD;
		ev->used = 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;
}

// remove ev from epfd
int nty_event_del(int epfd, struct ntyevent *ev) {

	struct epoll_event ep_ev = {0, {0}};

	if (ev->used != 1) {
		return -1;
	}

	ep_ev.data.ptr = ev;
	ev->used = 0;
	epoll_ctl(epfd, EPOLL_CTL_DEL, ev->fd, NULL);

	return 0;
}

还有其他一些函数一并写在这里

int start_listen(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));
	}

	printf("listening to port %hd with fd = %d\n", port, fd);
	return fd;
}


int ntyreactor_init(struct ntyreactor *reactor) {

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

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

	reactor->events = (struct ntyevent **)calloc(1, sizeof(struct ntyevent *));
	if (reactor->events == NULL) {
		printf("cannot allocate events block in %s\n", __func__);
		return -3;
	}
	reactor->block_num = 1;
	
	return 0;
}


int ntyreactor_destory(struct ntyreactor *reactor) {
	close(reactor->epfd);
	int i;
	for(i = 0; i < reactor->block_num; i++) {
		free(reactor->events[i]);
	}
	free(reactor->events);
}



int ntyreactor_addlistener(struct ntyreactor *reactor, int listenfd, NCALLBACK acceptor) {

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

	struct ntyevent *event = ntyreactor_get_event(reactor, listenfd);
	if (event == NULL) return -1;

	nty_event_update(event, listenfd, acceptor, reactor);
	event->sticky = 1; //don't close listen fd on timeout
	nty_event_add(reactor->epfd, EPOLLIN, event);

	return 0;
}

其他注意事项

为了达到百万连接数，我们还要增加系统的最大open files

使用

ulimit -a

查看open files

用-n设置，如果不行，就更改

sudo vim /etc/security/limits.conf

这个

末尾加上这两行

*                soft    nofile          1048576
*                hard    nofile          1048576

并且关掉shell并重新登录

此时应该就行了

并且可能还需要更改内核tcp收发缓存的大小

可以参考这里

参考资料

[1] 零声教育 Linux C/C++后端服务器架构开发 2.1网络开发

c/c++后台开发学习笔记 2.1.2 reactor原理与实现，实现百万级并发

reactor

其他注意事项

参考资料

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