cron公司内部是如何安排工作的?

How do "modern" cron daemons internally schedule their jobs? Some cronds used to schedule a run every so often via at. So after a crontab is written out, does crond:

“现代”守护进程如何在内部安排他们的工作?一些cronds经常通过at计划一次跑步。crontab写完后，crond:

1. Parse the crontab for all future events and the sleep for the intervals?
2. 为所有未来事件解析crontab，为间隔解析睡眠?
3. Poll an aggregated crontab database every minute to determine if the current time matches the schedule pattern?
4. 每分钟轮询聚合的crontab数据库，以确定当前时间是否与计划模式匹配?
5. Other?
6. 其他的吗?

Thanks,

谢谢,

1 个解决方案

#1

A few crickets heard in this question. Good 'ol RTFC with some discrete event simulation papers and Wikipedia:

在这个问题中听到了一些蟋蟀的叫声。好'ol RTFC与一些离散事件模拟文件和*:

http://en.wikipedia.org/wiki/Cron#Multi-user_capability

http://en.wikipedia.org/wiki/Cron Multi-user_capability

The algorithm used by this cron is as follows:

该cron使用的算法如下:

1. On start-up, look for a file named .crontab in the home directories of all account holders.
2. 在启动时，在所有帐户持有人的主目录中查找名为.crontab的文件。
3. For each crontab file found, determine the next time in the future that each command is to be run.
4. 对于找到的每个crontab文件，确定在未来的任何时候运行每个命令。
5. Place those commands on the Franta-Maly event list with their corresponding time and their "five field" time specifier.
6. 将这些命令放在Franta-Maly事件列表中，并使用相应的时间和“五个字段”时间说明符。
7. Enter main loop:
   1. Examine the task entry at the head of the queue, compute how far in the future it is to be run.
   2. 检查队列头部的任务条目，计算它在未来运行的距离。
   3. Sleep for that period of time.
   4. 睡上一段时间。
   5. On awakening and after verifying the correct time, execute the task at the head of the queue (in background) with the privileges of the user who created it.
   6. 在唤醒和验证正确的时间之后，以创建任务的用户的特权在队列的前端(后台)执行任务。
   7. Determine the next time in the future to run this command and place it back on the event list at that time
   8. 确定下一次运行该命令并将其返回到事件列表的下一次时间。
8. 输入主循环:检查队列头部的任务条目，计算它在未来运行的距离。睡上一段时间。在唤醒和验证正确的时间之后，以创建任务的用户的特权在队列的前端(后台)执行任务。确定下一次运行该命令并将其返回到事件列表的下一次时间。