Socket套接字编程（I/O复用 poll）

#include 
int poll(struct pollfd *fds, nfds_t nfds, int timeout);
	struct pollfd {
		int fd; /* 文件描述符 */
		short events; /* 监控的事件 */
		short revents; /* 监控事件中满足条件返回的事件 */
	};
	POLLIN			普通或带外优先数据可读,即POLLRDNORM | POLLRDBAND
	POLLRDNORM		数据可读
	POLLRDBAND		优先级带数据可读
	POLLPRI 		高优先级可读数据
	POLLOUT		普通或带外数据可写
	POLLWRNORM		数据可写
	POLLWRBAND		优先级带数据可写
	POLLERR 		发生错误
	POLLHUP 		发生挂起
	POLLNVAL 		描述字不是一个打开的文件

	nfds 			监控数组中有多少文件描述符需要被监控

	timeout 		毫秒级等待
		-1：阻塞等，#define INFTIM -1 				Linux中没有定义此宏
		0：立即返回，不阻塞进程
		>0：等待指定毫秒数，如当前系统时间精度不够毫秒，向上取值

如果不再监控某个文件描述符时，可以把pollfd中，fd设置为-1，poll不再监控此pollfd，下次返回时，把revents设置为0。

服务器端代码

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "wrap.h"

#define MAXLINE 80
#define SERV_PORT 6666
#define OPEN_MAX 1024

int main(int argc, char *argv[])
{
	int i, j, maxi, listenfd, connfd, sockfd;
	int nready;
	ssize_t n;
	char buf[MAXLINE], str[INET_ADDRSTRLEN];
	socklen_t clilen;
	struct pollfd client[OPEN_MAX];
	struct sockaddr_in cliaddr, servaddr;

	listenfd = Socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(SERV_PORT);

	Bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

	Listen(listenfd, 20);

	client[0].fd = listenfd;
	client[0].events = POLLRDNORM; 					/* listenfd监听普通读事件 */

	for (i = 1; i < OPEN_MAX; i++)
		client[i].fd = -1; 							/* 用-1初始化client[]里剩下元素 */
	maxi = 0; 										/* client[]数组有效元素中最大元素下标 */

	for ( ; ; ) {
		nready = poll(client, maxi+1, -1); 			/* 阻塞 */
		if (client[0].revents & POLLRDNORM) { 		/* 有客户端链接请求 */
			clilen = sizeof(cliaddr);
			connfd = Accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
			printf("received from %s at PORT %d\n",
					inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)),
					ntohs(cliaddr.sin_port));
			for (i = 1; i < OPEN_MAX; i++) {
				if (client[i].fd < 0) {
					client[i].fd = connfd; 	/* 找到client[]中空闲的位置，存放accept返回的connfd */
					break;
				}
			}

			if (i == OPEN_MAX)
				perr_exit("too many clients");

			client[i].events = POLLRDNORM; 		/* 设置刚刚返回的connfd，监控读事件 */
			if (i > maxi)
				maxi = i; 						/* 更新client[]中最大元素下标 */
			if (--nready <= 0)
				continue; 						/* 没有更多就绪事件时,继续回到poll阻塞 */
		}
		for (i = 1; i <= maxi; i++) { 			/* 检测client[] */
			if ((sockfd = client[i].fd) < 0)
				continue;
			if (client[i].revents & (POLLRDNORM | POLLERR)) {
				if ((n = Read(sockfd, buf, MAXLINE)) < 0) {
					if (errno == ECONNRESET) { /* 当收到 RST标志时 */
						/* connection reset by client */
						printf("client[%d] aborted connection\n", i);
						Close(sockfd);
						client[i].fd = -1;
					} else {
						perr_exit("read error");
					}
				} else if (n == 0) {
					/* connection closed by client */
					printf("client[%d] closed connection\n", i);
					Close(sockfd);
					client[i].fd = -1;
				} else {
					for (j = 0; j < n; j++)
						buf[j] = toupper(buf[j]);
						Writen(sockfd, buf, n);
				}
				if (--nready <= 0)
					break; 				/* no more readable descriptors */
			}
		}
	}
	return 0;
}

客户端代码如下

#include 
#include 
#include 
#include 
#include "wrap.h"
#define MAXLINE 80
#define SERV_PORT 6666

int main(int argc, char *argv[])
{
	struct sockaddr_in servaddr;
	char buf[MAXLINE];
	int sockfd, n;

	sockfd = Socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
	servaddr.sin_port = htons(SERV_PORT);

	Connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

	while (fgets(buf, MAXLINE, stdin) != NULL) {
		Write(sockfd, buf, strlen(buf));
		n = Read(sockfd, buf, MAXLINE);
		if (n == 0)
			printf("the other side has been closed.\n");
		else
			Write(STDOUT_FILENO, buf, n);
	}
	Close(sockfd);
	return 0;
}