IO多路复用poll函数

功能：阻塞函数，阻塞等待要监听的集合中的文件描述符准备就绪，如果有文件描述符准备就绪，则当前函数立即解除阻塞.
原型：
       #include <poll.h>

       int poll(struct pollfd *fds, nfds_t nfds, int timeout);
参数：
    struct pollfd *fds：要监控的文件描述符集合;与select的区别，select是以事件问单位，poll是以文件描述符为单位。
           struct pollfd {
               int   fd;         /* file descriptor */     要检测文件描述符
               short events;     /* requested events */    要检测的事件
               short revents;    /* returned events */     实际产生的事件
           };
        事件：
            POLLIN      读事件，有数据可读。     
            POLLOUT     写事件，有数据可写
            POLLERR     错误事件，只会出现在实际产生的时间中。
            
    nfds_t nfds：指定要监控的文件描述符个数;
    int timeout：
                >0, 超时时间；以ms为单位; 例如3s == 3000ms。
                <0, 如果不想设置超时时间，则填负数。
                =0，则该函数不阻塞，即使没有文件描述符准备就绪；
返回值：
    >0, 成功触发事件的文件描述符个数;
    =0, 超时，且没有文件描述符准备就绪
    =-1, 函数运行失败，更新errno;

使用poll函数 实现简单服务器和客户端

服务端支持并发连接,同时支持终端输入信息发送给客户端

客户端支持显示接收到的服务端消息, 同时支持终端输入消息发送服务器

server.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>
#include <sys/time.h>
#include <stdlib.h>
#include <poll.h>

#define PRINT_ERROR(msg) do{\
    fprintf(stderr, "line:__%d__ ", __LINE__);\
    perror(msg);\
    exit(-1);\
}while(0)

#define CONN_COUNT 10

int findIndex(struct pollfd* fds) {
    for (int i = 0; i < CONN_COUNT; i++) {
        if (*((int *)(fds + i)) == 0) {
            return i;
        }
    }
    return -1;
}

int main(int argc, const char *argv[]) {
    int sfd;
    if((sfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        PRINT_ERROR("socket");
    }
    int reuse = 1;
    if(setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0) {
        PRINT_ERROR("setsockopt");
    }
    struct sockaddr_in sin;
    sin.sin_family         = AF_INET;
    sin.sin_port         = htons(atoi(argv[2]));
    sin.sin_addr.s_addr = inet_addr(argv[1]);
    if(bind(sfd, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
        PRINT_ERROR("bind");
    }
    if(listen(sfd, 10) < 0) {
        PRINT_ERROR("listen");
    }
    int accept_fd = 0;
    int nbytes = 0;
    char buf[128] = {0};
    int p_res = 0;

    struct pollfd fds[CONN_COUNT] = {0};
    fds[0].fd = 0;
    fds[0].events = POLLIN;
    fds[1].fd = sfd;
    fds[1].events = POLLIN;
    int next = 2;

    while (1) {
        if ((p_res = poll(fds, next, 10000)) == -1) {
            PRINT_ERROR("select");
        } else if (p_res == 0) {
            printf("time out...\n");
        }
        if (fds[0].revents & POLLIN) {
            memset(buf, 0, sizeof(buf));
            int fd = 0;
            int res = scanf("%d %s", &fd, buf);
            while (getchar() != 10);
            if (res != 2 || fd > next) {
                printf("please input correct data\n");
                continue;
            }
            if (send(fd, buf, sizeof(buf), 0) == -1) {
                PRINT_ERROR("send");
            }
            p_res --;
        }
        if (fds[1].revents & POLLIN) {
            if ((accept_fd = accept(sfd, NULL, NULL)) == -1) {
                PRINT_ERROR("accept error");
            }
            printf("client [%d] connect!!!\n", accept_fd);
            fds[next].fd = accept_fd;
            fds[next].events = POLLIN;
            next ++;
            p_res --;
        }

        for (int i = 2; i < next && p_res != 0; i++) {
            if (fds[i].revents & POLLIN) {
                memset(buf, 0, sizeof(buf));
                if ((nbytes = recv(fds[i].fd, buf, sizeof(buf), 0)) == -1) {
                  PRINT_ERROR("recv error");
                } else if (nbytes == 0) {
                  printf("client [%d] disconnect !!!\n", i);
                  close(fds[i].fd);
                  for (int j = i; j < next; j++) {
                      fds[j] = fds[j + 1];
                  }
                  next --;
                  continue;
                }
                if (!strncmp(buf, "quit", 4)) {
                  printf("client [%d] disconnect !!!\n", fds[i].fd);
                  close(fds[i].fd);
                  for (int j = i; j < next; j++) {
                      fds[j] = fds[j + 1];
                  }
                  next --;
                  continue;
                }
                strcat(buf, "---hi !!!");
                if (send(fds[i].fd, buf, sizeof(buf), 0) == -1) {
                  PRINT_ERROR("send");
                }
                p_res --;
            }
        }
    }
    close(sfd);
    return 0;
}

client.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>
#include <sys/time.h>
#include <stdlib.h>
#include <poll.h>

#define PRINT_ERROR(msg) do{\
    fprintf(stderr, "line:__%d__ ", __LINE__);\
    perror(msg);\
    exit(-1);\
}while(0)

int main(int argc, const char *argv[]) {
    int sfd;
    if((sfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        PRINT_ERROR("socket");
    }
    struct sockaddr_in serveraddr;
    serveraddr.sin_family         = AF_INET;
    serveraddr.sin_port         = htons(atoi(argv[2]));
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);
    socklen_t serveraddr_len = sizeof(serveraddr);
    if (connect(sfd, (struct sockaddr *)&serveraddr, serveraddr_len) == -1) {
        PRINT_ERROR("connect error");
    }
    int accept_fd = 0;
    int nbytes = 0;
    char buf[128] = {0};
    int p_res = 0;

    struct pollfd fds[2] = {0};
    fds[0].fd = 0;
    fds[0].events = POLLIN;

    fds[1].fd = sfd;
    fds[1].events = POLLIN;
    
    while (1) {
        if ((p_res = poll(fds, 2, 10000)) == -1) {
            PRINT_ERROR("select");
        } else if (p_res == 0) {
            printf("time out...\n");
        }
        if (fds[0].revents & POLLIN) {
            memset(buf, 0, sizeof(buf));
            fgets(buf, sizeof(buf), stdin);
            buf[strlen(buf) - 1] = '\0';
            if (send(sfd, buf, sizeof(buf), 0) == -1) {
              PRINT_ERROR("send");
            }
            if (!strncmp(buf, "quit", 4)) {
              close(sfd);
              return 0;
            }
        }
        if (fds[1].revents & POLLIN) {
            memset(buf, 0, sizeof(buf));
            if ((nbytes = recv(sfd, buf, sizeof(buf), 0)) == -1) {
              PRINT_ERROR("recv error");
            } else if (nbytes == 0) {
                printf("server quit !!!!");
                break;
            }
            printf("receive ----> %s\n", buf);
        }
    }
    close(sfd);
    return 0;
}

执行结果

server

ubuntu@ubuntu:~ $ ./server 127.0.0.1 8889
client [4] connect!!!
client [5] connect!!!
4 hi
5 hello
client [5] disconnect !!!
client [4] disconnect !!!
^C
ubuntu@ubuntu:~ $

client1

ubuntu@ubuntu:~ $ ./client 127.0.0.1 8889
1
receive ----> 1---hi !!!
2
receive ----> 2---hi !!!
3
receive ----> 3---hi !!!
receive ----> hi
quit
ubuntu@ubuntu:~ $

client2

ubuntu@ubuntu:~ $ ./client 127.0.0.1 8889
a
receive ----> a---hi !!!
b
receive ----> b---hi !!!
c
receive ----> c---hi !!!
receive ----> hello
quit
ubuntu@ubuntu:~ $