文件 IO

int select(int maxfdp, fd_set* readfds, fd_set* writefds, fd_set* exceptfds, timeval* tvptr);

int FD_ISSET(int fd, fd_set* fdset); // 若 fd 在 fdset 中，返回非零值

int FD_CLR(int fd, fd_set* fdset);
int FD_SET(int fd, fd_set* fdset);
int FD_ZERO(fd_set* fdset);

int pselect(int maxfdp, fd_set* readfds, fd_set* writefds, fd_set* exceptfds, const timespec* tvptr, sigset_t* sigmask);

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <strings.h>
#include <sys/select.h>
#include <unistd.h>

int main(int argc, char* argv[]) {
    int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
    assert(flags >= 0);
    flags |= O_NONBLOCK;
    fcntl(STDIN_FILENO, F_SETFL, flags);

    fd_set readFds;
    fd_set excFds;
    FD_ZERO(&readFds);
    FD_ZERO(&excFds);
    char buf[255];
    int  ret;
    while(1) {
        bzero(buf, 255);
        FD_SET(STDIN_FILENO, &readFds);
        FD_SET(STDIN_FILENO, &excFds);
        ret = select(STDIN_FILENO + 1, &readFds, NULL, &excFds, NULL);
        assert(ret >= 0);
        if(FD_ISSET(STDIN_FILENO, &readFds)) {
            read(STDIN_FILENO, buf, 255);
            write(STDOUT_FILENO, buf, 255);
        } else if(FD_ISSET(STDIN_FILENO, &excFds)) {
            fprintf(stderr, "errno = %d", errno);
        }
    }
    return 0;
}

int poll(pollfd* fdarray, nfds_t nfds, int timeout);

struct pollfd{
   int fd; // 需要监控的文件描述符
   short events; // 需要监控的事件
   short revents; // 实际发生的事件
};

#include <assert.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char* argv[]) {
    int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
    assert(flags >= 0);
    flags |= O_NONBLOCK;
    fcntl(STDIN_FILENO, F_SETFL, flags);

    int            nfds = 1;
    struct pollfd* pfds;
    pfds = calloc(nfds, sizeof(struct pollfd));
    assert(pfds != NULL);
    pfds[0].fd = STDIN_FILENO;
    pfds[0].events |= POLLIN;
    while(1) {
        int ready;
        ready = poll(pfds, 1, -1);
        assert(ready != -1);
        fprintf(stderr, "Ready: %d\n", ready);

        char buf[255];
        memset(buf, '\0', 255);
        for(int i = 0; i < nfds; ++i) {
            if(pfds[i].revents & POLLIN) {
                ssize_t l = read(pfds[i].fd, buf, 255);
                write(STDOUT_FILENO, buf, 255);
            }
        }
    }
    return 0;
}

int epoll_create(int size);
int epoll_ctl(int epfd, int op, int fd, epoll_event* event);
int epoll_wait(int epfd, epoll_event* events, int maxevents, int timeout);

struct epoll_event {
   uint32_t events; // 与 poll 能监视的事件差不多，只是宏名前面加了个E
   epoll_data_t data; // 用户数据，除了能保存文件描述符以外，还能保存一些其它有关数据
};

typedef union epoll_data {
   void        *ptr;
   int          fd;
   uint32_t     u32;
   uint64_t     u64;
} epoll_data_t;

#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/epoll.h>
#include <unistd.h>

int main(int argc, char* argv[]) {
    int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
    assert(flags >= 0);
    flags |= O_NONBLOCK;
    fcntl(STDIN_FILENO, F_SETFL, flags);

    int epfd = epoll_create1(0);
    assert(epfd != -1);
    struct epoll_event ev;
    struct epoll_event events[10];
    ev.events  = EPOLLIN | EPOLLET;
    ev.data.fd = STDIN_FILENO;
    int rtn    = epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev);
    assert(rtn != -1);

    int  nfds = 0;
    char buf[255];
    while(1) {
        nfds = epoll_wait(epfd, events, 10, -1);
        assert(nfds != -1);
        for(size_t i = 0; i < nfds; ++i) {
            int fd = events[i].data.fd;
            bzero(buf, 255);
            read(fd, buf, 255);
            write(STDOUT_FILENO, buf, 255);
        }
    }
    return 0;
}