CopyOnWriteArray

最新推荐文章于 2024-12-04 08:40:45 发布

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本文深入解析了CopyOnWriteArrayList的实现原理，包括其线程安全的add、set和contains方法的具体实现细节。CopyOnWriteArrayList通过复制底层数组并在新副本上进行修改来确保线程安全性，避免了迭代时的并发修改异常。

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public class CopyOnWriteArrayList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable{
	
	private transient volatile Object[] array;
	
	public boolean contains(Object o) {
        Object[] elements = getArray();
        return indexOf(o, elements, 0, elements.length) >= 0;
    }
    
    
	public boolean add(E e) {
        	final ReentrantLock lock = this.lock;
       		lock.lock();
        	try {
            	Object[] elements = getArray();
            	int len = elements.length;
            	Object[] newElements = Arrays.copyOf(elements, len + 1);
            	newElements[len] = e;
            	setArray(newElements);
           	 	return true;
       	 	} finally {
            	lock.unlock();
        	}
    }
    
	public E set(int index, E element) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            E oldValue = get(elements, index);

            if (oldValue != element) {
                int len = elements.length;
                Object[] newElements = Arrays.copyOf(elements, len);
                newElements[index] = element;
                setArray(newElements);
            } else {
                // Not quite a no-op; ensures volatile write semantics
                setArray(elements);
            }
            return oldValue;
        } finally {
            lock.unlock();
        }
    }
}