Guarded Suspension 守衛模式

能處理多客戶端請求，若柱列區無資料時，處理元件就等待， 若有新加入，元件將會啟用。

@Slf4j
public abstract class AbtractCmd<T> implements ICommand<T> {

	private volatile LinkedList<T> list = new LinkedList<T>();
	private final int size;//柱列限制筆數

	public AbtractCmd(int size) {
		this.size = size;
	}

	public synchronized void add(T i) {
		boolean canAdd = this.canAdd();
		if (canAdd) {
			this.list.add(i);
			log.info("list:{}, add item:{}", this.list, i);
			notifyAll();
		} else {
			try {
				wait();
				this.add(i);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}

	}

	private boolean canAdd() {
		return list.size() < size;
	}

	@Override
	public synchronized T execute() throws InterruptedException {
		if (!this.ready()) {
//			log.info("wait job");
			wait();
		} else {
			T poll = this.list.poll();
			notifyAll();
			return poll;

		}
		return execute();

	}

	private boolean ready() {
		return !list.isEmpty();
	}

	@Override
	public boolean isEmpty() {
		return list.isEmpty();
	}

}