epoll的helloworld
转https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/说明：介绍来自http://baike.baidu.com/view/1385104.htm
epoll是Linux下多路复用IO接口select/poll的增强版本，它能显著提高程序在大量并发连接中只有少量活跃的情况下的系统CPU利用率，因为它不会复用文件描述符集合来传递结果而迫使开发者每次等待事件之前都必须重新准备要被侦听的文件描述符集合，另一点原因就是获取事件的时候，它无须遍历整个被侦听的描述符集，只要遍历那些被内核IO事件异步唤醒而加入Ready队列的描述符集合就行了。epoll除了提供select/poll那种IO事件的电平触发（Level Triggered）外，还提供了边沿触发（Edge Triggered），这就使得用户空间程序有可能缓存IO状态，减少epoll_wait/epoll_pwait的调用，提高应用程序效率。
官方的运行不了，有错误，看我这个
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/socket.h>#include <netdb.h>#include <unistd.h>#include <fcntl.h>#include <sys/epoll.h>#include <errno.h>#define MAXEVENTS 64static intmake_socket_non_blocking (int sfd){int flags, s;flags = fcntl (sfd, F_GETFL, 0);if (flags == -1) { perror ("fcntl"); return -1; }flags |= O_NONBLOCK;s = fcntl (sfd, F_SETFL, flags);if (s == -1) { perror ("fcntl"); return -1; }return 0;}static intcreate_and_bind (char *port){struct addrinfo hints;struct addrinfo *result, *rp;int s, sfd;memset (&hints, 0, sizeof (struct addrinfo));hints.ai_family = AF_UNSPEC; /* Return IPv4 and IPv6 choices */hints.ai_socktype = SOCK_STREAM; /* We want a TCP socket */hints.ai_flags = AI_PASSIVE; /* All interfaces */s = getaddrinfo (NULL, port, &hints, &result);if (s != 0) { fprintf (stderr, "getaddrinfo: %s\n", gai_strerror (s)); return -1; }for (rp = result; rp != NULL; rp = rp->ai_next) { sfd = socket (rp->ai_family, rp->ai_socktype, rp->ai_protocol); if (sfd == -1) continue; s = bind (sfd, rp->ai_addr, rp->ai_addrlen); if (s == 0) { /* We managed to bind successfully! */ break; } close (sfd); }if (rp == NULL) { fprintf (stderr, "Could not bind\n"); return -1; }freeaddrinfo (result);return sfd;}intmain (int argc, char *argv[]){int sfd, s;int efd;struct epoll_event event;struct epoll_event *events;if (argc != 2) { fprintf (stderr, "Usage: %s \n", argv); exit (EXIT_FAILURE); }sfd = create_and_bind (argv);if (sfd == -1) abort ();s = make_socket_non_blocking (sfd);if (s == -1) abort ();s = listen (sfd, SOMAXCONN);if (s == -1) { perror ("listen"); abort (); }efd = epoll_create (0);//error in original pageif (efd == -1) { perror ("epoll_create"); abort (); }event.data.fd = sfd;event.events = EPOLLIN | EPOLLET;s = epoll_ctl (efd, EPOLL_CTL_ADD, sfd, &event);if (s == -1) { perror ("epoll_ctl"); abort (); }/* Buffer where events are returned */events = calloc (MAXEVENTS, sizeof event);/* The event loop */while (1) { int n, i; n = epoll_wait (efd, events, MAXEVENTS, -1); for (i = 0; i < n; i++){if ((events.events & EPOLLERR) || (events.events & EPOLLHUP) || (!(events.events & EPOLLIN))) { /* An error has occured on this fd, or the socket is not ready for reading (why were we notified then?) */ fprintf (stderr, "epoll error\n"); close (events.data.fd); continue; }else if (sfd == events.data.fd) { /* We have a notification on the listening socket, which means one or more incoming connections. */ while (1) { struct sockaddr in_addr; socklen_t in_len; int infd; char hbuf, sbuf; in_len = sizeof in_addr; infd = accept (sfd, &in_addr, &in_len); if (infd == -1) { if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) { /* We have processed all incoming connections. */ break; } else { perror ("accept"); break; } } s = getnameinfo (&in_addr, in_len, hbuf, sizeof hbuf, sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV); if (s == 0) { printf("Accepted connection on descriptor %d " "(host=%s, port=%s)\n", infd, hbuf, sbuf); } /* Make the incoming socket non-blocking and add it to the list of fds to monitor. */ s = make_socket_non_blocking (infd); if (s == -1) abort (); event.data.fd = infd; event.events = EPOLLIN | EPOLLET; s = epoll_ctl (efd, EPOLL_CTL_ADD, infd, &event); if (s == -1) { perror ("epoll_ctl"); abort (); } } continue; } else { /* We have data on the fd waiting to be read. Read and display it. We must read whatever data is available completely, as we are running in edge-triggered mode and won't get a notification again for the same data. */ int done = 0; while (1) { ssize_t count; char buf; count = read (events.data.fd, buf, sizeof buf); if (count == -1) { /* If errno == EAGAIN, that means we have read all data. So go back to the main loop. */ if (errno != EAGAIN) { perror ("read"); done = 1; } break; } else if (count == 0) { /* End of file. The remote has closed the connection. */ done = 1; break; } /* Write the buffer to standard output */ s = write (1, buf, count); if (s == -1) { perror ("write"); abort (); } } if (done) { printf ("Closed connection on descriptor %d\n", events.data.fd); /* Closing the descriptor will make epoll remove it from the set of descriptors which are monitored. */ close (events.data.fd); } } } }free (events);close (sfd);return EXIT_SUCCESS;}
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