poll和select的区别不大，主要是poll没有连接数限制，因为它用的链表实现
#include <poll.h>int poll(struct pollfd *fds, nfds_t nfds, int timeout);
struct pollfd {int fd; //要监控的文件描述符,如果fd为-1, 表示内核不再监控short events; //输入参数, 表示告诉内核要监控的事件, 读事件, 写事件, 异常事件short revents; //输出参数, 表示内核告诉应用程序有哪些文件描述符有事件发生
};
events/revents:POLLIN:可读事件POLLOUT: 可写事件POLLERR: 异常事件
nfds: 告诉内核监控的范围, 具体是: 数组下标的最大值+1
timeout: =0: 不阻塞, 立刻返回-1: 表示一直阻塞, 直到有事件发生>0: 表示阻塞时长, 在时长范围内若有事件发生会立刻返回;如果超过了时长也会立刻返回
函数返回值:>0: 发生变化的文件描述符的个数=0: 没有文件描述符发生变化-1: 表示异常
使用poll来监控多个文件描述符进行客户端通信
代码：
#include "socketwrap.h"
#include <arpa/inet.h>
#include <poll.h>
#include <strings.h>
#include <string.h>
#include <ctype.h>#define POLLLEN 1024int main()
{int sfd = Socket(AF_INET, SOCK_STREAM, 0);// 设置端口复用int opt = 1;setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(int));struct sockaddr_in soaddr;bzero(&soaddr, sizeof(soaddr));soaddr.sin_family = AF_INET;soaddr.sin_port = htons(9999);soaddr.sin_addr.s_addr = htonl(INADDR_ANY);Bind(sfd, (struct sockaddr *)&soaddr, sizeof(soaddr));// 监听-listenListen(sfd, 128);struct pollfd connfd[POLLLEN];int maxfd; // 当前需要监听的最大的文件描述符int nready; // 返回的需要处理的个数int cfd; // 通信描述符int i, maxi = 0;struct sockaddr_in clientsocket;socklen_t clilen;char buff[64]; // 通信数据// 初始化有效的文件描述符数组for (int i = 0; i < POLLLEN; i++){bzero(&connfd[i], sizeof(connfd[i]));connfd[i].fd = -1;}maxfd = sfd;connfd[0].fd = sfd;connfd[0].events = POLLIN;while (1){clilen = sizeof(clientsocket);bzero(&clientsocket, clilen);nready = poll(connfd, maxfd + 1, -1);if (nready < 0){if (errno == EINTR) // 被信号中断{continue;}perror("poll error");break;}if (nready > 0){if (connfd[0].revents == POLLIN){// 有连接到来cfd = Accept(sfd, (struct sockaddr *)&clientsocket, &clilen);for (i = 0; i < POLLLEN; i++){if (connfd[i].fd == -1){connfd[i].events = POLLIN;connfd[i].fd = cfd;maxi = i;if (maxfd < cfd){maxfd = cfd;}// 打印客户端的IP和PORTchar sIP[16];memset(sIP, 0x00, sizeof(sIP));printf("client [%s:%d] connect\n", inet_ntop(AF_INET, &clientsocket.sin_addr.s_addr, sIP, sizeof(sIP)), htons(clientsocket.sin_port));break;}}if (i == POLLLEN){close(cfd);printf("connect too much, server busy\n");continue;}if (--nready == 0){continue;}}for (i = 1; i <= maxi; i++){if (connfd[i].fd == -1){continue;}if (connfd[i].revents == POLLIN){// 有数据发送过来int n;int sockfd = connfd[i].fd;memset(buff, 0x00, sizeof(buff));n = Read(sockfd, buff, sizeof(buff));if (n < 0){perror("read over");close(sockfd);bzero(&connfd[i], sizeof(bzero));connfd[i].fd = -1; // 将connfd[i]置为-1,表示该位置可用}else if (n == 0){// printf("client is closed\n");close(sockfd);bzero(&connfd[i], sizeof(bzero));connfd[i].fd = -1; // 将connfd[i]置为-1,表示该位置可用}else{printf("[%d]:[%s]\n", n, buff);for (i = 0; i < n; i++){buff[i] = toupper(buff[i]);}Write(sockfd, buff, n);}if (--nready <= 0){break; // 注意这里是break,而不是continue, 应该是从最外层的while继续循环}}}}}close(sfd);return 0;
}