Method drain

src/main/java/cms/component/topic/HotTopicComponent.java:161–188

批量消费（调用不删除唯一标记API） 来自 https://github.com/google/guava/blob/master/guava/src/com/google/common/collect/Queues.java @param q @param buffer @param numElements @param timeout @param unit @return @throws InterruptedException

(UniqueBlockingQueue<E> q,Collection<? super E> buffer,int numElements,long timeout,TimeUnit unit)

	 * @throws InterruptedException
	 */
	@CanIgnoreReturnValue
	@GwtIncompatible // BlockingQueue
	@SuppressWarnings("GoodTime") // should accept a java.time.Duration
	private <E> int drain(UniqueBlockingQueue<E> q,Collection<? super E> buffer,int numElements,long timeout,TimeUnit unit)
		      throws InterruptedException {
		Preconditions.checkNotNull(buffer);
	    /*
	     * This code performs one System.nanoTime() more than necessary, and in return, the time to
	     * execute Queue#drainTo is not added *on top* of waiting for the timeout (which could make
	     * the timeout arbitrarily inaccurate, given a queue that is slow to drain).
	     */
		long deadline = System.nanoTime() + unit.toNanos(timeout);
		int added = 0;
		while (threadActivity && added < numElements) {
			// we could rely solely on #poll, but #drainTo might be more efficient when there are multiple
		    // elements already available (e.g. LinkedBlockingQueue#drainTo locks only once)
		    added += q.drainTo2(buffer, numElements - added);
		    if (added < numElements) { // not enough elements immediately available; will have to poll
		        E e = q.poll2(deadline - System.nanoTime(), TimeUnit.NANOSECONDS);
		        if (e == null) {
		        	break; // we already waited enough, and there are no more elements in sight
		        }
		        buffer.add(e);
		        added++;
		    }
		}
		return added;
	}
	
	/**
	 * 初始化数据