1、BlockingQueue

BlockingQueue為阻塞佇列，其與普通佇列不同的是，以put和get為例，阻塞佇列在put時，若列表滿了，則會等待直到佇列可以加入元素；而阻塞佇列在get時候，若列表為空，則會等待到佇列非空。可以用來解決 生產者消費者問題。

2、ArrayBlockingQueue

阻塞佇列在add時，若列表滿了，則丟擲異常；

阻塞佇列在offer時根據不同引數決定；

阻塞佇列在put時，若列表滿了，則會等待直到佇列可以加入元素；

阻塞佇列在get時候，若列表為空，則會等待到佇列非空。

特點：通過一個lock進行實現，存取共用一個鎖，並且是先進先出FIFO；

原始碼中該阻塞佇列提供了3個建構函式：

    // 通過指定佇列的大小
    public ArrayBlockingQueue(int capacity) {
        this(capacity, false);
    }

    // 佇列大小 以及 是否建立公平鎖 true為公平鎖  false為非公平鎖
    public ArrayBlockingQueue(int capacity, boolean fair) {
        if (capacity <= 0)
            throw new IllegalArgumentException();
        this.items = new Object[capacity];
        lock = new ReentrantLock(fair);
        notEmpty = lock.newCondition();
        notFull =  lock.newCondition();
    }

    // 將佇列c元素都加入初始化的佇列中
    public ArrayBlockingQueue(int capacity, boolean fair,
                              Collection<? extends E> c) {
        this(capacity, fair);

        final ReentrantLock lock = this.lock;
        lock.lock(); // Lock only for visibility, not mutual exclusion
        try {
            int i = 0;
            try {
                for (E e : c) {
                    checkNotNull(e);
                    items[i++] = e;
                }
            } catch (ArrayIndexOutOfBoundsException ex) {
                throw new IllegalArgumentException();
            }
            count = i;
            putIndex = (i == capacity) ? 0 : i;
        } finally {
            lock.unlock();
        }
    }

從上面可以瞭解到，ArrayBlockQueue是指定大小的，並且是通過ReentrantLock（實現公平鎖和非公平鎖）來進行鎖定

ArrayBlockQueue的add（e）實際就是呼叫了offer（e）
// 根據程式碼就是獲取到ReentranLock 通過加鎖和解鎖 來實現
    public boolean offer(E e) {
        checkNotNull(e);
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                enqueue(e);
                return true;
            }
        } finally {
            lock.unlock();
        }
    }
// 加入到佇列中，putIndex 在每次執行完後都回加一，即表示下次放入陣列中的元素
    private void enqueue(E x) {
        // assert lock.getHoldCount() == 1;
        // assert items[putIndex] == null;
        final Object[] items = this.items;
        items[putIndex] = x;
        if (++putIndex == items.length)
            putIndex = 0;
        count++;
        // 標記表示該佇列非空，等待中的消費者可以進行執行
        notEmpty.signal();
    }

// offer中有一個方法為在指定時間內，若佇列滿則等等
    public boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException {

        checkNotNull(e);
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == items.length) {
                if (nanos <= 0)
                    return false;
                nanos = notFull.awaitNanos(nanos);
            }
            enqueue(e);
            return true;
        } finally {
            lock.unlock();
        }
    }

// put則為一直等待 知道佇列非滿
    public void put(E e) throws InterruptedException {
        checkNotNull(e);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == items.length)
                notFull.await();
            enqueue(e);
        } finally {
            lock.unlock();
        }
    }

阻塞佇列的take

// 從阻塞佇列中獲取元素
    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        // 獲取鎖，若中斷則獲取 資料失敗
        lock.lockInterruptibly();
        try {
            // 若沒有元素則等待 則到notEmpty條件被清除notEmpty.signal();
            while (count == 0)
                notEmpty.await();
            return dequeue();
        } finally {
            lock.unlock();
        }
    }

// 從佇列中取出元素takeIndex 與putIndex類似初始值為0，遍歷完一次take後從0從新開始，遵循先進先出
    private E dequeue() {
        // assert lock.getHoldCount() == 1;
        // assert items[takeIndex] != null;
        final Object[] items = this.items;
        @SuppressWarnings("unchecked")
        E x = (E) items[takeIndex];
        items[takeIndex] = null;
        if (++takeIndex == items.length)
            takeIndex = 0;
        count--;
        if (itrs != null)
            itrs.elementDequeued();//同時更新迭代器中的元素資料
        // 置為非滿佇列
        notFull.signal();
        return x;
    }

3、LinkedBlockingQueue

private final ReentrantLock putLock = new ReentrantLock();寫入元素的鎖指定為非公平鎖

/** Wait queue for waiting puts */
private final Condition notFull = putLock.newCondition();

private final ReentrantLock takeLock = new ReentrantLock(); 取出元素的鎖，被指定為非公平鎖。

/** Wait queue for waiting takes */
private final Condition notEmpty = takeLock.newCondition();

特點：通過存取鎖分別用兩個鎖，都為非公平鎖，（可以有效的防止共用一個鎖時，一直被寫鎖lock而讀鎖一直得不到鎖的情況）文中以讀鎖和寫鎖相稱：

同樣通過構造器檢視：

    // 生成一個沒有大小限制的連結串列
    public LinkedBlockingQueue() {
        this(Integer.MAX_VALUE);
    }

    // 指定大小的連結串列
    public LinkedBlockingQueue(int capacity) {
        if (capacity <= 0) throw new IllegalArgumentException();
        this.capacity = capacity;
        last = head = new Node<E>(null);
    }
    // 將其他佇列中的元素加入該連結串列
    public LinkedBlockingQueue(Collection<? extends E> c) {
        this(Integer.MAX_VALUE);
        final ReentrantLock putLock = this.putLock;
        putLock.lock(); // Never contended, but necessary for visibility
        try {
            int n = 0;
            for (E e : c) {
                if (e == null)
                    throw new NullPointerException();
                if (n == capacity)
                    throw new IllegalStateException("Queue full");
                enqueue(new Node<E>(e));
                ++n;
            }
            count.set(n);
        } finally {
            putLock.unlock();
        }
    }

加入元素的方法：

    // 加入元素 
    public boolean offer(E e) {
        if (e == null) throw new NullPointerException();
        final AtomicInteger count = this.count;//判斷是否為指定容器大小，使用原子包裝，這樣可以獲取實施的count，防止被take了這裡卻還未減少數量
        if (count.get() == capacity) // 若等於容器則返回false
            return false;
        int c = -1;
        Node<E> node = new Node<E>(e);
        final ReentrantLock putLock = this.putLock;// 獲取寫鎖並進行鎖定
        putLock.lock();
        try {
            if (count.get() < capacity) {
                enqueue(node);
                c = count.getAndIncrement();
                if (c + 1 < capacity)
                    notFull.signal();
            }
        } finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
        return c >= 0;
    }

    // 加入佇列只需要使其下一個節點設值
    private void enqueue(Node<E> node) {
        // assert putLock.isHeldByCurrentThread();
        // assert last.next == null;
        last = last.next = node;
    }

    // 獲取讀鎖，並將非空條件去除
    private void signalNotEmpty() {
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lock();
        try {
            notEmpty.signal();
        } finally {
            takeLock.unlock();
        }
    }
    

// put方法
    public void put(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        // Note: convention in all put/take/etc is to preset local var
        // holding count negative to indicate failure unless set.
        int c = -1;
        Node<E> node = new Node<E>(e);
        final ReentrantLock putLock = this.putLock;
        final AtomicInteger count = this.count;
        putLock.lockInterruptibly();
        try {
            /*
             * Note that count is used in wait guard even though it is
             * not protected by lock. This works because count can
             * only decrease at this point (all other puts are shut
             * out by lock), and we (or some other waiting put) are
             * signalled if it ever changes from capacity. Similarly
             * for all other uses of count in other wait guards.
             */
            while (count.get() == capacity) {
                notFull.await();//若滿則釋放寫鎖，並等待
            }
            enqueue(node);
            c = count.getAndIncrement();
            if (c + 1 < capacity)
                notFull.signal();
        } finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
    }

取出元素：

// 取出元素 鎖定讀鎖，
    public E take() throws InterruptedException {
        E x;
        int c = -1;
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lockInterruptibly();
        try {
            while (count.get() == 0) {
                notEmpty.await(); //若為空 則釋放讀鎖並等待
            }
            x = dequeue();
            c = count.getAndDecrement();
            if (c > 1)
                notEmpty.signal();
        } finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }
// 標記為佇列非滿狀態
    private void signalNotFull() {
        final ReentrantLock putLock = this.putLock;
        putLock.lock();
        try {
            notFull.signal();
        } finally {
            putLock.unlock();
        }
    }

4、待續。。。