p5.c

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

struct timer_t {
  unsigned int started_at;  // 设置定时器时的 UNIX 时间戳
  unsigned int ended_at;    // 设置的定时器应该触发的 UNIX 时间戳
  void (*proc)();           // 超时执行的函数
  struct timer_t *next;     // 指向下一个定时器
};

struct timer_t *head = NULL;

/**
 * 向队列中添加一个定时器
 * 返回最近一个要触发的闹钟时间的余留秒数
 */
unsigned int push_to_timer_list(struct timer_t *node) {
  unsigned int cur_time;
  time((time_t *)&cur_time);

  struct timer_t *cur = head;

  /* 若当前没有待触发的定时器 */
  if (cur == NULL) {
    head = node;
    alarm(node->ended_at - cur_time);
    return (head->ended_at - cur_time);
  } else {
    /* 如果添加的定时器先于之前的第一个定时器 */
    if (head->ended_at > node->ended_at) {
      node->next = head;
      head = node;
      alarm(node->ended_at - cur_time);
      return (node->ended_at - cur_time);
    } else {
      /* 移动游标 */
      while (cur->next && cur->next->ended_at < node->ended_at) {
        cur = cur->next;
      }
      node->next = cur->next;
      cur->next = node;
      return (head->ended_at - cur_time);
    }
  }
}

/**
 * 触发指定的事件并启动下一个定时器
 */
void alarm_proc(int signo) {
  struct timer_t *cur;
  cur = head;
  cur->proc();

  if (cur->next) {
    alarm(cur->next->ended_at - cur->ended_at);
    free(head);
    head = cur->next;
  } else {
    free(head);
    head = NULL;
  }
}

/**
 * 类似于 JavsScript 的 settimeout 函数
 * 参数是定时器的时间以及超时后执行的函数
 */
void settimeout(unsigned int seconds, void (*proc)()) {
  /* 如果时间为 0 ，则直接执行 */
  if (seconds == 0) {
    proc();
    return;
  }

  struct timer_t *t = (struct timer_t *)malloc(sizeof(struct timer_t));
  time((time_t *)&(t->started_at));
  t->ended_at = t->started_at + seconds;
  t->next = NULL;
  t->proc = proc;

  if (signal(SIGALRM, alarm_proc) == SIG_ERR) {
    printf("signal (SIGALRM) error\n");
    exit(0);
  }

  push_to_timer_list(t);
}

void print() { printf("Hello World\n"); }

void print2() { printf("Hello MeiK\n"); }

int main() {
  settimeout(2, print);
  settimeout(1, print);
  settimeout(5, print);
  settimeout(3, print2);
  printf("Hello main\n");
  for (;;) {
    pause();
  }
  return 0;
}