LinkedBlockingDeque自動阻塞，put和take方法的阻塞實現

LinkedBlockingDeque自動阻塞的雙端隊列。
增刪元素的方法都是用ReentrantLock上鎖的。
add方法無返回值，滿了報異常，offer方法滿了return false，put方法滿了await自動阻塞。

以putFirst(E e)爲例：

final ReentrantLock lock = new ReentrantLock();
private final Condition notFull = lock.newCondition();
public void putFirst(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        Node<E> node = new Node<E>(e);
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            while (!linkFirst(node))//returns false if full.
                notFull.await(); //實現list滿了的情況下就會自動阻塞
        } finally {
            lock.unlock();
        }
    }

以pollFirst()爲例，peek，get等方法均不阻塞

public E pollFirst() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return unlinkFirst();
        } finally {
            lock.unlock();
        }
    }

只有take方法是自動阻塞的，調用condition的await方法進行阻塞

public E takeFirst() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E x;
            while ( (x = unlinkFirst()) == null)
                notEmpty.await();
            return x;
        } finally {
            lock.unlock();
        }
    }