epoll lt应用

子进程往pipe管道写，父进程监听管道输入事件，从管道读取子进程发送的数据。

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdlib.h>
#include <sys/epoll.h>
#define MSG_MAX_SIZE 100
 
void sys_error(const char *str)
{
    perror(str);
    exit(1);
}
 
int main(void)
{
    int ret;
    char buf[MSG_MAX_SIZE]; //message buffer
    int fd[2];//pipe fd array,to restore the read & write end of the pipe.
    
    ret = pipe(fd);//pipefd[0] refers to the read end of the pipe.  pipefd[1] refers to the write end of  the pipe.
    if (ret == -1)
        sys_error("pipe open failure");

    pid_t pid;
    pid = fork();//create a child process

    if (pid == -1)
        sys_error("fork an sub process fail");
    else if (pid == 0)//it is a child process. in this demo,child process act as a writor.
    {
        close(fd[0]); // child process close the read end;
        int msg_no = 0;
        while (1)
        {
            msg_no++;
            sprintf(buf,"message no.%d",msg_no);
            write(fd[1], buf, sizeof(buf));//write sth via the write end.
            printf("%30s%s\n","child process send:",buf);
            sleep(2);
        }
    }
    else
    {//it is the parent process, and acts as a reader.
        close(fd[1]); //parent proc close the write end.
        int epfd = epoll_create(512); // open an epoll file descriptor.
        if (epfd == -1)
            sys_error("epoll_create failure");

        // interested event .
        //pipefd[0] refers to the read end of the pipe.  pipefd[1] refers to the write end of  the pipe.
        struct epoll_event read_event;
        read_event.events = EPOLLIN; //The associated file is available for read(2) operations.
        read_event.data.fd = fd[0];//parent process will read via fd[0] 
        
        int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd[0], &read_event);
        if (ret == -1)
            sys_error("epoll_ctl failure");

        struct epoll_event output_events[1]; //output parameters,to restore the I/O event associated fd
        int all_events;
        while (1)
        {
            all_events = epoll_wait(epfd, output_events, 1, 0); // wait for an I/O event on an epoll file descriptor
            if (all_events == -1)
                sys_error("epoll_wait failure");
            else if (all_events > 0)//I/O event on an epoll file descriptor,read data via fd[0]
            {
                read(fd[0], buf, MSG_MAX_SIZE);
                printf("%30s%s\n\n","parent process receive:",buf);
            } else{
            }
        }
        close(fd[0]);
        close(epfd);
    }
 
    return 0;
}

运行结果：