【RTS笔记5】Timer

Soft Timer Facility

Clock and Timer

clock：不断增加，显示现在时间
Timer：不断减少（倒计时），时间到发出提醒

Hard Timers & Soft Timers

• Hard Timers ：are derived from physical timer chips that directly interrupt the processor when they expire.
• Soft Timers ：are software events that are scheduled through a software timer facility.
  
  

Handling Multiple Timers 处理多个计时器

A soft timer facility is a system tool that allows timers to be set up for which we can tolerate some bounded inaccuracy.

The soft timer facility has three main functions:

1. Timer maintenance, i.e., counting down a timer.
2. Timer installation, i.e., starting a timer.
3. Timer removal, i.e., stopping a timer.