select , poll , epoll I/O Multiplexing(I/O多路复用)
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关于 I/O multiplexing:
—————-这里简单介绍一下,详细请参考UNP/ linux/UNIX系统编程手册下册
其实“I/O多路复用”这个坑爹翻译可能是这个概念在中文里面如此难理解的原因。所谓的I/O多路复用在英文中其实叫 I/O multiplexing,基本是这个意思:
I/O multiplexing 这里面的 multiplexing 指的其实是在单个线程通过记录跟踪每一个Sock(I/O流)的状态来同时管理多个I/O流. 发明它的原因,是尽量多的提高服务器的吞吐能力。
epoll和read 都是阻塞的
read 和 epoll等阻塞的内容不一样,前者阻塞在整个IO调用上,后者阻塞在等待IO事件通知(多路复用就是多个文件句柄的多个状态变更通知)
select poll epoll不管是单路还是多路,都需要有个线程在那阻塞等事件通知,通知有数据了,就调用你的回调函数; 对用户程序来说,就是一个模拟的AIO。
就一个单刀多置开关,哪搞事情,就连哪。
第一套:select:
struct fd_set { __fd_mask_bits[N] };
先来几个结构体,存放要监听的读写,异常事件。
(1) fd_set read_fds; //读fd_set write_fds; //写
(2) FD_ZERO( &read_fds );FD_ZERO( &write_fds );listenfd = listen(...)
(3)while(1) FD_SET(listenfd, &read_fds);FD_SET(connfd, &read_fds);FD_SET(connfd, &write_fds);int select(int nfds 文件描述符总数, fd_set *readfds 可读, fd_set *writefds 可写, fd_set *exceptfds 异常, struct timeval *timeout 超时时间);if FD_ISSET(connfd, &read_fds) //发生读事件if FD_ISSET(connfd, &write_fds) //发生写事件相关函数, 宏定义: FD_ZERO(fd_set *fdset); //清空集合FD_SET(int fd, fd_set *fdset); //将一个给定的文件描述符加入集合之中FD_CLR(int fd, fd_set *fdset); //将一个给定的文件描述符从集合中删除int FD_ISSET(int fd, fd_set *fdset); // 检查集合中指定的文件描述符是否可以读写
select回射服务器:
#include <iostream>#include<mynet.h>using namespace std;#define BUF_SIZE 1024#define LISTEN_MAX 1000int main() { cout << "TCP select 回射服务器!" << endl; int maxi, maxfd, listenfd, connfd, sockfd, num, i; int nready, client[FD_SETSIZE]; ssize_t n; fd_set rset, allset; socklen_t cli_len; struct sockaddr_in cliaddr, servaddr; char buf[BUF_SIZE]; listenfd = socket(AF_INET, SOCK_STREAM, 0); int resuse = 1; setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &resuse, sizeof(resuse)); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(10086); inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr); bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)); listen(listenfd, LISTEN_MAX); maxfd = listenfd; maxi = -1; for(int i = 0; i < FD_SETSIZE; i++) { client[i] = -1; } FD_ZERO(&allset); FD_SET(listenfd, &allset); while(1) { rset = allset; printf("selecting\n"); nready = select(maxfd+1, &rset, NULL, NULL, NULL); printf("%d\n",nready); printf("selected\n"); if(FD_ISSET(listenfd, &rset)) { cli_len = sizeof(cliaddr); connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &cli_len); printf("connfd: %d", connfd); printf("Get new one client\n"); for(i = 0; i < maxfd; i++) { if (client[i] < 0) { client[i] = connfd; break; } } FD_SET(connfd, &allset); if(connfd > maxfd) maxfd = connfd; if(i > maxi) maxi = i; nready --; if(nready <= 0) continue; } for(i = 0; i <= maxi; i++) { if((sockfd = client[i]) < 0) continue; if( FD_ISSET(sockfd, &rset)) { n = read(sockfd, buf, sizeof(buf)); if(n == 0) { printf("lost a client\n"); close(sockfd); FD_CLR(sockfd, &allset); client[i] = -1; } else{ write(sockfd, buf, n); } nready --; if(nready <= 0) break; } } } return 0;}
第二套:poll
fcntl(fd, F_SETFL, O_NONBLOCK)pollfd fds[]; //要监听的事件集合
struct pollfd {int fd; /* file descriptor */short events; /* requested events */short revents; /* returned events */};
fds[0].fd = listenfd;fds[0].events = POLLIN | POLLERR //监听fd 只关注 读取,错误事件,,不可能有写事件fds[0].revents = 0;
while(1){ ret = poll(fds, user_counter+1, -1)//int poll(struct pollfd *fds, nfds_t nfds, int timeout);for(0 -- user_counter){ if(fds[i].fd == listenfd && fds[i].revents & POLLIN){/**/ if fds[i].revents & POLLIN //读事件 if fds[i].revents & POLLOUT //写事件}
poll 回射服务器:
/************************************************************************* > File Name: server.cpp > Author: dulun > Mail: dulun@xiyoulinux.org > Created Time: 2016年07月19日 星期二 11时26分40秒 ************************************************************************/#include<iostream>#include<stdio.h>#include<string.h>#include<stdlib.h>#include<algorithm>#include<sys/socket.h>#include<sys/types.h>#include<netinet/in.h>#include<arpa/inet.h>#include<assert.h>#include<fcntl.h>#include<poll.h>#include<errno.h>#include<unistd.h>using namespace std;#define USER_LIMIT 100#define BUFFER_SIZE 64#define FD_LIMIT 65535struct client_data{ sockaddr_in address; char * write_buff; char buf[BUFFER_SIZE];};int setnonblocking( int fd ){ int old_option = fcntl( fd, F_GETFL ); int new_option = old_option | O_NONBLOCK; fcntl( fd, F_SETFL, new_option ); return old_option;}int main(){ const char *ip = "127.0.0.1"; int port = 10086; 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); int listenfd = socket(PF_INET, SOCK_STREAM, 0); int resuse = 1; setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &resuse, sizeof(resuse)); assert(listenfd >= 0); int ret; ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address)); //命名套接字。 assert(ret != -1); ret = listen(listenfd, USER_LIMIT); //监听 assert(ret != -1); client_data * users = new client_data[FD_LIMIT]; pollfd fds[USER_LIMIT+1]; int user_counter = 0; for(int i = 1; i <= USER_LIMIT; i++) { fds[i].fd = -1; fds[i].events = 0; } //初始化第一个 fds[0].fd = listenfd; fds[0].events = POLLIN | POLLERR; fds[0].revents = 0; while(1) { ret = poll( fds, user_counter+1, -1 ); if(ret < 0) { printf("POLL failed\n"); break; } for(int i = 0; i < user_counter+1; i++) { if((fds[i].fd == listenfd) && (fds[i].revents & POLLIN) ) { struct sockaddr_in client_address; socklen_t client_addrlength = sizeof(client_data); int connfd = accept(listenfd, (struct sockaddr*)&client_address, &client_addrlength); printf("accept\n"); if(connfd < 0) { printf("errno is : %d \n", errno); continue; } if(user_counter >= USER_LIMIT) { const char * info = "too many users\n"; printf("%s", info); send(connfd, info, strlen(info), 0); close(connfd); continue; } user_counter++; users[connfd].address = client_address; setnonblocking(connfd); fds[user_counter].fd = connfd; fds[user_counter].events = POLLIN | POLLERR; fds[user_counter].revents = 0; printf("comes a new user, now have %d users\n", user_counter); } else if(fds[i].revents & POLLERR) //ERROR , fds[i].revent & POLLERR 为真,表示,发生错误,下同 { printf("get an error form %d\n", fds[i].fd); char errors[100]; memset(errors, 0, sizeof(errors)); socklen_t length = sizeof(errors); if( getsockopt(fds[i].fd, SOL_SOCKET, SO_ERROR, &errors, &length) < 0) { printf("get socket option failed\n"); } continue; } else if(fds[i].revents & POLLRDHUP) { //users[fds[i].fd] = users[fds[user_counter].fd]; close(fds[i].fd); //fds[i] = fds[] printf("a client left\n"); sleep(1); } else if(fds[i].revents & POLLIN) { int connfd = fds[i].fd; memset(users[connfd].buf, 0, BUFFER_SIZE); ret = recv(connfd, users[connfd].buf, BUFFER_SIZE-1, 0); send(connfd, users[connfd].buf, BUFFER_SIZE-1, 0); if(ret == 0) { close(connfd); printf("one client left\n"); user_counter--; i--; continue; } printf("get %d bytes of client data %s from %d \n", ret, users[connfd].buf, connfd); //sleep(10000); //test! if(ret < 0) { if(errno != EAGAIN) { close(connfd); users[fds[i].fd] = users[fds[user_counter].fd]; fds[i] = fds[user_counter]; i--; user_counter--; } } else if( ret == 0 ) { } else{ for(int j = 1; j <= user_counter; j++) { if(fds[j].fd == connfd) //不等于自己,不给自己设置读写事件 { continue; } //fds[j].events |= ~POLLIN; //取消读事件 fds[j].events |= POLLOUT; //设置写事件,下次while循环,直接进下一个else if users[fds[j].fd].write_buff = users[connfd].buf; } } } else if(fds[i].revents & POLLOUT) //监听到写事件(次数:user_counter-1) { int connfd = fds[i].fd; if( !users[connfd].write_buff ) { continue; } ret = send(connfd, users[connfd].write_buff, strlen(users[connfd].write_buff)-1, 0); //往过发 users[connfd].write_buff = NULL; //清缓存 // fds[i].events |= ~POLLOUT; //取消写时间 // fds[i].events |= POLLIN; //设置读事件 } } } delete []users; close(listenfd); return 0;}
poll零拷贝客户端:
(splice + pipe 重定向标准输入到套接字描述符
/************************************************************************* > File Name: client.c > Author: dulun > Mail: dulun@xiyoulinux.org > Created Time: 2016年07月19日 星期二 11时01分09秒 ************************************************************************/#include<stdio.h>#include<string.h>#include<stdlib.h>#include<unistd.h>#include<netinet/in.h>#include<arpa/inet.h>#include<sys/types.h>#include<sys/socket.h>#include<poll.h>#include<fcntl.h>#include<assert.h>#define BUFFER_SIZE 64int main(){ // const char * ip = "115.159.53.185"; const char * ip = "127.0.0.1"; //int port = 6550; int port = 10086; 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("connetcion failed\n"); close(sockfd); return 1; } printf("connetc over!\n"); pollfd fds[2]; //0:标准输入 fds[0].fd = 0; fds[0].events = POLLIN; //可读事件 fds[0].revents = 0; //内核处理 //1:套接字描述符 fds[1].fd = sockfd; fds[1].events = POLLIN | POLLRDHUP; //可读或对方中断 fds[1].revents = 0; char read_buf[BUFFER_SIZE]; //读缓存, 用于接收 int pipefd[2]; int ret = pipe(pipefd); assert(ret != -1); while(1) { ret = poll(fds, 2, -1); //阻塞,监听两个感兴趣的fd if(ret < 0) { printf("poll failed\n"); break; } if(fds[1].revents & POLLRDHUP) { printf("server close the connetcion\n"); break; } else if( fds[1].revents & POLLIN ) { memset( read_buf, 0, BUFFER_SIZE ); recv(fds[1].fd, read_buf, BUFFER_SIZE - 1, 0); printf("%s\n", read_buf); } if(fds[0].revents & POLLIN) { //标准输入输出 通过管道 。去sockfd //从标准输入读 ,进管道, 大小32768 更多或文件直接走内核缓冲区 ret = splice( 0, NULL, pipefd[1], NULL, 32768 , SPLICE_F_MORE | SPLICE_F_MOVE); // pipefd[0] 读 //从管道读, 进套接字描述符, 大小32768 更多或文件直接走内核缓冲区 ret = splice( pipefd[0], NULL, sockfd, NULL, 32768 , SPLICE_F_MORE | SPLICE_F_MOVE); //写 } } close(sockfd); return 0;}
第三套 epoll:
传统的select/poll另一个致命弱点就是当你拥有一个很大的socket集合,不过由于网络延时,任一时间只有部分的socket是”活跃”的, 但是select/poll每次调用都会线性扫描全部的集合,导致效率呈现线性下降 o(n)
但是epoll不存在这个问题,它只会对”活跃”的socket进行 操作—这是因为在内核实现中epoll是根据每个fd上面的callback函数实现的。那么,只有”活跃”的socket才会主动的去调用 callback函数,其他idle状态socket则不会,在这点上,epoll实现了一个”伪”AIO,因为这时候推动力在os内核。在一些 benchmark中,如果所有的socket基本上都是活跃的—比如一个高速LAN环境,epoll并不比select/poll有什么效率,相 反,如果过多使用epoll_ctl,效率相比还有稍微的下降。但是一旦使用idle connections模拟WAN环境,epoll的效率就远在select/poll之上了。
要使用epoll只需要这三个系统调 用:epoll_create(2), epoll_ctl(2), epoll_wait(2)。
epoll_create(2) creates an epoll instance and returns a file descriptor referring to that instance.
(The more recent epoll_create1(2) extends the functionality of epoll_create(2).)
//epoll_creat(系统调用) 创建一个epoll事件,并且返回一个文件描述符指向那个事件Interest in particular file descriptors is then registered via epoll_ctl(2). The set of file descriptors currently registered on an epoll instance is sometimes called an epoll set.
//(对某些特定的有兴趣的文件描述符,通过epoll_ctl(系统调用)进行注册),文件描述符集合一般注册在一个epoll 例子,称为 epoll setepoll_wait(2) waits for I/O events, blocking the calling thread if no events are currently available.
//eppll_wait(系统调用)等待I/O事件,如果当前没有事件发生,阻塞于调用的线程,
结构体:
epoll_event events[]
epollfd = epoll_create(0) //返回指向内核中文件描述符
epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event); //加入一个描述符到内核监听队列
基本使用逻辑
(a) 使用epoll_create()函数创建文件描述,设定将可管理的最大socket描述符数目。
(b) 创建与epoll关联的接收线程,应用程序可以创建多个接收线程来处理epoll上的读通知事件,线程的数量依赖于程序的具体需要。
(c) 创建一个侦听socket描述符ListenSock;将该描述符设定为非阻塞模式,调用Listen()函数在套接字上侦听有无新的连接请求,
在 epoll_event结构中设置要处理的事件类型EPOLLIN,工作方式为 epoll_ET,以提高工作效率,同时使用epoll_ctl()注册事件,最后启动网络监视线程。
(d) 网络监视线程启动循环,epoll_wait()等待epoll事件发生。
(e) 如果epoll事件表明有新的连接请求,则调用accept()函数,将用户socket描述符添加到epoll_data联合体,同时设定该描述符为非 阻塞,并在epoll_event结构中设置要处理的事件类型为读和写,工作方式为epoll_ET.
(f) 如果epoll事件表明socket描述符上有数据可读,则将该socket描述符加入可读队列,通知接收线程读入数据,并将接收到的数据放入到接收数据 的链表中,经逻辑处理后,将反馈的数据包放入到发送数据链表中,等待由发送线程发送。
epoll 回射服务器:
/************************************************************************* > File Name: server2.cpp > Author: dulun > Mail: dulun@xiyoulinux.org > Created Time: 2016年07月20日 星期三 09时12分28秒 ************************************************************************/#include<iostream>#include<stdio.h>#include<string.h>#include<stdlib.h>#include<algorithm>#include<sys/socket.h>#include<sys/types.h>#include<netinet/in.h>#include<arpa/inet.h>#include<assert.h>#include<errno.h>#include<unistd.h>#include<fcntl.h>#include<sys/epoll.h>#include<pthread.h>#define MAX_EVENT_NUMBER 1024#define TCP_BUFFER_SIZE 512#define UDP_BUFFER_SIZE 1024int setnonblocking(int fd){ int old_opt = fcntl(fd, F_GETFL); int new_opt = old_opt | O_NONBLOCK; fcntl(fd, F_SETFL, new_opt); return old_opt;}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); setnonblocking(fd);}int main(){ const char * ip = "127.0.0.1"; int port = 10086; int ret = 0; struct sockaddr_in address; address.sin_family = AF_INET; inet_pton(AF_INET, ip, &address.sin_addr); address.sin_port = htons(port); int listenfd = socket(PF_INET, SOCK_STREAM, 0); assert(listenfd >= 0); int resuse = 1; setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &resuse, sizeof(resuse)); ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address)); assert(ret != -1); ret = listen(listenfd, 5); assert(ret != -1); bzero(&address, sizeof(address)); address.sin_family = AF_INET; inet_pton(AF_INET, ip, &address.sin_addr); address.sin_port = htons(port); int udpfd = socket(PF_INET, SOCK_DGRAM, 0); assert(udpfd >= 0); ret = bind(udpfd, (struct sockaddr *)&address, sizeof(address)); epoll_event events[MAX_EVENT_NUMBER]; int epollfd = epoll_create(5); addfd(epollfd, listenfd); addfd(epollfd, udpfd); while(1) { int number = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1); if(number < 0) { printf("epoll failed"); 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_addrelength = sizeof(client_address); int connfd = accept(listenfd, (struct sockaddr*)&client_address, &client_addrelength); addfd(epollfd, connfd); } else if(sockfd == udpfd) { char buf[UDP_BUFFER_SIZE]; memset(buf, 0, sizeof(buf)); struct sockaddr_in client_address; socklen_t client_addresslength = sizeof(client_address); ret = recvfrom(udpfd, buf, UDP_BUFFER_SIZE-1, 0, (struct sockaddr*)&client_address, &client_addresslength); if(ret > 0) { sendto(udpfd, buf, UDP_BUFFER_SIZE - 1, 0, (struct sockaddr *) &client_address, client_addresslength); } } else if(events[i].events & EPOLLIN) { char buf[TCP_BUFFER_SIZE]; while(1) { memset(buf, 0, sizeof(buf)); ret = recv(sockfd, buf, TCP_BUFFER_SIZE - 1, 0); if(ret < 0) { if(errno == EAGAIN || errno == EWOULDBLOCK) { break; } close(sockfd); break; } else if(ret == 0) { close(sockfd); } else { send(sockfd, buf, ret, 0);//回射 } } } else{ printf("somethin else happened \n"); } } } close(listenfd); return 0;}
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