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Three or four timers is usually the reliable limit .

三或四个计时器通常是可接受的上限。

Many watchdog timers have a maximum period of around two seconds .

很多看门狗定时器有一个大约2秒钟的最大周期。

Timers on desks push older students as they practise racing through tests .

为了通过测试，年纪大一些的学生则在计时器的催促下练习赛跑。

For those embedded systems that can 't be constantly watched by a human , watchdog timers may be the solution .

对那些不能始终有人看护的嵌入式系统，看门狗定时器可能是解决方案。

These events can be things like timers , signals , data ready for reading on a file descriptor , and so on .

这些事件可以是诸如计时器，信号，文件描述符上预备读取的数据，等等。