Implementing Semaphore

Problem Statement

Java does provide its own implementation of Semaphore, however, Java's semaphore is initialized with an initial number of permits, rather than the maximum possible permits and the developer is expected to take care of always releasing the intended number of maximum permits.

Briefly, a semaphore is a construct that allows some threads to access a fixed set of resources in parallel. Always think of a semaphore as having a fixed number of permits to give out. Once all the permits are given out, requesting threads, need to wait for a permit to be returned before proceeding forward.

Your task is to implement a semaphore which takes in its constructor the maximum number of permits allowed and is also initialized with the same number of permits.

Solution

Given the above definition we can now start to think of what functions our Semaphore class will need to expose. We need a function to "gain the permit" and a function to "return the permit".

1. acquire() function to simulate gaining a permit
2. release() function to simulate releasing a permit

The constructor accepts an integer parameter defining the number of permits available with the semaphore. Internally we need to store a count which keeps track of the permits given out so far.

The skeleton for our Semaphore class looks something like this so far.

public class CountingSemaphore {

    int usedPermits =