运行循环如何工作？

Question

Out a curiosity, how does a Run Loop work? The official docs say

The purpose of a run loop is to keep your thread busy when there is work to do and put your thread to sleep when there is none.

How is this implemented efficiently? Is the run loop actually a loop that is constantly running? ie. while(true) ?

Answer 1

I understand it as something waiting for inputs to come to do things.

For example, when you use your phone, the screen is displaying things but at the same time it is waiting for any inputs to come do stuff. Inputs can be you touching the screen, someone sending you a text, some scheduled alarm ready to ring, etc.

Thus using a run loop would be describing all the accepted inputs (events, schedule, etc.) with handlers, and when that is done, start waiting for those inputs to come.

The purpose of a run loop is to keep your thread busy when there is work to do and put your thread to sleep when there is none.

This means that every time your loop is waiting for inputs, concerned thread will be idle, and once an input comes, the thread will be active and execute the stuff it needs to.