传递到 epoll_ctl 的epoll事件结构体如下所示。对每一个被监听的描述符,你可以关联到一个整数或一个作为用户数据的指针。
typedef union epoll_data { void *ptr; int fd; __uint32_t u32; __uint64_t u64; } epoll_data_t; struct epoll_event { __uint32_t events; /* Epoll events */ epoll_data_t data; /* User data variable */ };马上实践写代码。我们会实现一个小的TCP服务器,它会将所有SOCKET上收到的数据输出到标准输出。 首先写一个 create_and_bind() 函数,它创建并绑定一个TCP socket.
static int create_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; }
create_and_bind函数包含了一种可移植方式来获取IPv4或IPv6套接字的标准代码段。它接受一个port的字符串参数,port是从argv[1]中传入的。其中,getaddrinfo函数返回一群addrinfo到result,其中它们跟传入的hints参数是兼容的。 addrinfo结构体如下:
struct addrinfo { int ai_flags; int ai_family; int ai_socktype; int ai_protocol; size_t ai_addrlen; struct sockaddr *ai_addr; char *ai_canonname; struct addrinfo *ai_next; };我们依次遍历这些结构体并用其来创建结构体,直到我们可以同时创建和绑定到socket。如果我们成功,create_and_bind() 会返回一个socket描述符。失败则返回 -1.
static int make_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; }
现在,有一个包含事件循环的main()函数,下面就是代码:
#define MAXEVENTS 64 int main (int argc, char *argv[]) { int sfd, s; int efd; struct epoll_event event; struct epoll_event *events; if (argc != 2) { fprintf (stderr, "Usage: %s [port]\n", argv[0]); exit (EXIT_FAILURE); } sfd = create_and_bind (argv[1]); 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_create1 (0); if (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[i].events & EPOLLERR) || (events[i].events & EPOLLHUP) || (!(events[i].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[i].data.fd); continue; } else if (sfd == events[i].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[NI_MAXHOST], sbuf[NI_MAXSERV]; 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[512]; count = read (events[i].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[i].data.fd); /* Closing the descriptor will make epoll remove it from the set of descriptors which are monitored. */ close (events[i].data.fd); } } } } free (events); close (sfd); return EXIT_SUCCESS; }
main() 首先调用 create_and_bind()来新建一个socket。然后将其设置为非阻塞,再调用 listen (2)。之后,我们新建一个epoll实例inefd,并将监听套接字sfd以采用边沿触发的方式加入它,用以监听输入事件。
在外面的while循环是主要的事件循环。它调用epoll_wait(2),它所在线程以阻塞的方式来等待事件的到来。当事件就绪,epoll_wait(2)在其epoll_event类型的参数中返回相应的事件。
当我们添加新的传入连接,当他们终止时我们删除现有的连接,epoll 的实例 inefdis 的事件循环不断更新。
当事件的状态为可用的时候,他们有以下三种类型:
下载 epoll-example.c 代码.
更新1: 水平和边缘触发的定义被错误的颠倒使用(尽管代码是正确的)。首先被Reddit用户bodski发现. 现在文章已经修正。 我应该在发布之前校读一次。向读者致歉并感谢你们指出错误。 :)
更新2: 代码被改为直到提示将被阻塞时才执行 accept(2) ,这样如果多个连接到达,我们可以接收全部请求。首先被Reddit用户cpitchford发现. 感谢你的评论。 :)
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