Method poll2

src/main/java/cms/utils/UniqueBlockingQueue.java:165–168

将首个元素从队列中弹出,如果队列是空的，就返回null。不删除唯一标记

(long timeout, TimeUnit unit)

	 * 将首个元素从队列中弹出,如果队列是空的，就返回null。不删除唯一标记
	 */
	public T poll2(long timeout, TimeUnit unit) throws InterruptedException {
	    T e = mBlockingQueue.poll(timeout, unit);
	    return e;
	}
	
	/**
	 * 删除唯一标记