epoll_etlt.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <errno.h>
#include <unistd.h>
#define MAXLINE 10
int main(int argc, char *argv[])
{
int efd, i;
int pfd[2];
pid_t pid;
char buf[MAXLINE], ch = 'a';
pipe(pfd);
pid = fork();
if (pid == 0) { //子 写
close(pfd[0]);
while (1) {
//aaaa\n
for (i = 0; i < MAXLINE/2; i++)
buf[i] = ch;
buf[i-1] = '\n';
ch++;
//bbbb\n
for (; i < MAXLINE; i++)
buf[i] = ch;
buf[i-1] = '\n';
ch++;
//aaaa\nbbbb\n
write(pfd[1], buf, sizeof(buf));
sleep(5);
}
close(pfd[1]);
} else if (pid > 0) { //父 读
struct epoll_event event;
struct epoll_event resevent[10]; //epoll_wait就绪返回event
int res, len;
close(pfd[1]);
efd = epoll_create(10);
event.events = EPOLLIN | EPOLLET; // ET 边沿触发
//event.events = EPOLLIN; // LT 水平触发 (默认)
event.data.fd = pfd[0];
epoll_ctl(efd, EPOLL_CTL_ADD, pfd[0], &event);
while (1) {
res = epoll_wait(efd, resevent, 10, -1);
printf("res %d\n", res);
if (resevent[0].data.fd == pfd[0]) {
len = read(pfd[0], buf, MAXLINE/2);
write(STDOUT_FILENO, buf, len);
}
}
close(pfd[0]);
close(efd);
} else {
perror("fork");
exit(-1);
}
return 0;
}
该程序创建了1个子进程,用于写数据; 父进程用于读数据.我们通过在父进程中控制每次读取的字节数来模拟缓冲区中数据未被全部读完的情况,此时只有水平触发模式才能从epoll_wait函数返回,并继续读取; 边沿触发在epoll_wait阻塞,直到下一次子进程发送数据才会继续读取缓冲区的数据.
程序46行,我们通过代码event.events = EPOLLIN | EPOLLET; 将epoll设置为边沿触发,如果要设置为水平触发,注释该行代码即可.
