redis源码学习：基于epoll_wait的定时器及示例

redis的定时任务是死循环+epoll_wait延时来实现的。其函数调用顺序是：

redis.c main 调用ae.c aeMain (死循环)
    ae.c aeMain 调用 ae.c aeProcessEvents:
        ae.c aeProcessEvents 调用 ae.c aeSearchNearestTimer(获取定时任务里下一个需要执行的任务)
        ae.c aeProcessEvents 调用 ae_poll.c aeApiPoll(设置epoll_wait)
            epoll_wait超时触发后，执行redis.c serverCron (由serverCron来调用各种具体的定时任务)

用epoll_wait实现定时器的示例：

#define MAX_EVENTS 1
#include <stdio.h>     // for fprintf()
#include <unistd.h>    // for close(), read()
#include <sys/epoll.h> // for epoll_create1(), epoll_ctl(), struct epoll_event
#include <string.h>    // for strncmp

void serverCron(){
  printf("serverCron is called\n");
}

int main()
{
  int running = 1, event_count;
  struct epoll_event event, events[1];
  int epoll_fd = epoll_create(1024);

  if(epoll_fd == -1)
  {
    fprintf(stderr, "Failed to create epoll file descriptor\n");
    return 1;
  }

  if(epoll_ctl(epoll_fd, EPOLL_CTL_ADD, 0, &event))
  {
    fprintf(stderr, "Failed to add file descriptor to epoll\n");
    close(epoll_fd);
    return 1;
  }
 
  while(running)
  {
    event_count = epoll_wait(epoll_fd, events, MAX_EVENTS, 1000);
    serverCron();
  }


  if(close(epoll_fd))
  {
    fprintf(stderr, "Failed to close epoll file descriptor\n");
    return 1;
  }
  return 0;
}

《redis源码学习笔记概要》