java-显式condition对象

1、在某些情况下，当内部锁非常不灵活时，显式锁就可以派上用场。内部条件队列有一些缺陷，每个内部锁只能有一个与之相关联的条件队列。

2、使用显式的Lock和Condition的实现类提供了一个比内部锁和条件队列更加灵活的选择。一个Condition和一个单独的Lock相关联，就像条件队列和单独的内部锁相关联一样。每个锁可以有多个等待集、中断性选择、基于时限、公平性选择等。

public interface Condition{

   void await() throws InterruptedException;//相当于wait

   boolean await(long time,TimeUnit unit) throws InterruptedException;

   long awaitNanos(long nanosTimeout) throws InterruptedException;

   void awaitUninterruptibly();

   boolean awaitUntil(Date deadline) throws InterruptedException;

 

   void signal();//相当于notify

   void signalAll();//相当于notifyall

}

调用与Condition相关联的Lock的Lock.newCondition方法，可创建一个Condition.

3、有限缓存操作

@ThreadSafe

public class ConditionBoundedBuffer<T>{

   protected final Lock lock=new ReentrantLock();

   private final Condition notFull=lock.newCondition();

   private final Condition notEmpty=lock.newCondition();

   @GuardBy("lock");

   private final T[] items=(T[]) new Object[BUFFER_SIZE];

   @GuardBy("lock") private int tail,head,count;

  

   public void put(T x) throws InterruptedExceptoin{

       lock.lock();

       try{

           while (count=items.lentgh)

                notFull.await();

           items[tail]=x;

           if (++tail=items.length)

               tail=0;

           ++count;

           notEmpty.signal();

       }

       finally{lock.unlock();

       }

   }

  

   public T take() throws InterruptedException{

       lock.lock();

       try{

           while (count=items.lentgh)

                notEmpty.await();

           T x=items[head];

           items[head]=null;

           if (++head=items.length)

               head=0;

           --count;

           notFull.signal();

          return x;

       }

       finally{lock.unlock();

       }

   }

  

  

}