Java多線程併發經常使用類實例之：Condition

        做爲一個示例，假定有一個綁定的緩衝區，它支持 put 和 take 方法。若是試圖在空的緩衝區上執行 take 操做，則在某一個項變得可用以前，線程將一直阻塞；若是試圖在滿的緩衝區上執行 put 操做，則在有空間變得可用以前，線程將一直阻塞。咱們喜歡在單獨的等待 set 中保存 put 線程和 take 線程，這樣就能夠在緩衝區中的項或空間變得可用時利用最佳規劃，一次只通知一個線程。可使用兩個 Condition 實例來作到這一點。

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();
     }
   } 
 }