源码

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JUC

AbstractQueuedSynchronizer

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public  Abstract class AbstractQueuedSynchronized{
	
	private static final long STATE;
	private transient volatile Node head;  
	private transient volatile Node tail;
		
	//之所以没有设置abstract, 是因为这是一个模板, 有些方法未必所有子类的都有用, 如果abstract修饰
	//那子类为了避免成为抽象类就必须重写它不需要的方法
	protected boolean tryAcquire(int arg) {  
	    throw new UnsupportedOperationException();  
	}
	
	protected boolean tryRelease(int arg) {  
	    throw new UnsupportedOperationException();  
	}
	
	protected int tryAcquireShared(int arg) {  
	    throw new UnsupportedOperationException();  
	}
	
	final void enqueue(ConditionNode node) {  
	    if (node != null) {  
	        boolean unpark = false;  
		    while(true) {  
		            Node t;  
		            if ((t = this.tail) == null && (t = this.tryInitializeHead()) == null) {  
		                unpark = true;  
		                break;  
		            }  
		            node.setPrevRelaxed(t);  
		            if (this.casTail(t, node)) {  
		                t.next = node;  
		                if (t.status < 0) {  
		                    unpark = true;  
		                }  
		                break;  
		            }  
		    }  
		       if (unpark) {  
		          LockSupport.unpark(node.waiter);  
		    }  
		}  
	  
	}
		
		
}