Java多线程并发经常使用类实例之：Condition

        做为一个示例，假定有一个绑定的缓冲区，它支持 put 和 take 方法。若是试图在空的缓冲区上执行 take 操做，则在某一个项变得可用以前，线程将一直阻塞；若是试图在满的缓冲区上执行 put 操做，则在有空间变得可用以前，线程将一直阻塞。咱们喜欢在单独的等待 set 中保存 put 线程和 take 线程，这样就能够在缓冲区中的项或空间变得可用时利用最佳规划，一次只通知一个线程。可使用两个 Condition 实例来作到这一点。

class BoundedBuffer {
   final Lock lock = new ReentrantLock();
   final Condition notFull  = lock.newCondition(); 
   final Condition notEmpty = lock.newCondition(); 

   final Object[] items = new Object[100];
   int putptr, takeptr, count;

   public void put(Object x) throws InterruptedException {
     lock.lock();
     try {
       while (count == items.length) 
         notFull.await();
       items[putptr] = x; 
       if (++putptr == items.length) putptr = 0;
       ++count;
       notEmpty.signal();} finally {
       lock.unlock();
     }
   }

   public Object take() throws InterruptedException {
     lock.lock();
     try {
       while (count == 0) 
         notEmpty.await();
       Object x = items[takeptr]; 
       if (++takeptr == items.length) takeptr = 0;
       --count;
       notFull.signal5();
       return x;
     } finally {
       lock.unlock();
     }
   } 
 }