Why is Symaphore needed in java.util.concurrent?

Question

Java

It seems that this is a counter that gives false if == 0 and can itself increase its number by timeout, but how can this be applied in reality?
and a couple more questions:
Why is StampedLock needed and why is tryLock needed in ReentrantLock?
I tried to figure it out, but I did not find a clear answer on how to apply it.

Answer 1

habra