Java基于Semaphore构建阻塞对象池

  public Semaphore(int permits) {
    sync = new NonfairSync(permits);
  }
  public Semaphore(int permits, boolean fair) {
    sync = fair ? new FairSync(permits) : new NonfairSync(permits);
  }

  public void acquire() throws InterruptedException {
    sync.acquireSharedInterruptibly(1);
  }
  public void release() {
    sync.releaseShared(1);
  }

public class SemaphoreUsage<T> {

  private final Set<T> set;
  private final Semaphore sem;

  public SemaphoreUsage(int bound){
    this.set = Collections.synchronizedSet(new HashSet<T>());
    sem= new Semaphore(bound);
  }

  public boolean add (T o) throws InterruptedException{
    sem.acquire();
    boolean wasAdded = false;
    try{
      wasAdded=set.add(o);
      return wasAdded;
    }finally {
      if(!wasAdded){
        sem.release();
      }
    }
  }

  public boolean remove(Object o){
    boolean wasRemoved = set.remove(o);
    if(wasRemoved){
      sem.release();
    }
    return wasRemoved;
  }
}