使用Lock实现信号量

public class SemaphoreOnLock
{

    private final Lock lock = new ReentrantLock();

   

    private final Condition permitsAvailable = lock.newCondition();

   

    private int permits;

   

    SemaphoreOnLock(int initialPermits)

    {

        lock.lock();

       

        try

        {

            permits = initialPermits;

        }

        finally

        {

            lock.unlock();

        }

    }

   

    public void acquire()

        throws InterruptedException

    {

        lock.lock();

       

        try

        {

            while (permits <= 0)

            {

                permitsAvailable.await();

            }

           

            --permits;

        }

        finally

        {

            lock.unlock();

        }

    }

   

    public void release()

    {

        lock.lock();

       

        try

        {

            ++permits;

            permitsAvailable.signal();

        }

        finally

        {

            lock.unlock();

        }

       

    }

}