Merge "Add separate enqueue and dequeue interfaces for queue"

namespace bluetooth {

namespace os {

// See documentation for |Queue|

template <typename T>

class Queue {

class IQueueEnqueue {

 public:

  using EnqueueCallback = std::function<std::unique_ptr<T>()>;

  virtual ~IQueueEnqueue() = default;

  virtual void RegisterEnqueue(Handler* handler, EnqueueCallback callback) = 0;

  virtual void UnregisterEnqueue() = 0;

};

// See documentation for |Queue|

template <typename T>

class IQueueDequeue {

 public:

  using DequeueCallback = std::function<void()>;

  virtual ~IQueueDequeue() = default;

  virtual void RegisterDequeue(Handler* handler, DequeueCallback callback) = 0;

  virtual void UnregisterDequeue() = 0;

  virtual std::unique_ptr<T> TryDequeue() = 0;

};

template <typename T>

class Queue : public IQueueEnqueue<T>, public IQueueDequeue<T> {

 public:

  // A function moving data from enqueue end buffer to queue, it will be continually be invoked until queue

  // is full. Enqueue end should make sure buffer isn't empty and UnregisterEnqueue when buffer become empty.

  ~Queue();

  // Register |callback| that will be called on |handler| when the queue is able to enqueue one piece of data.

  // This will cause a crash if handler or callback has already been registered before.

  void RegisterEnqueue(Handler* handler, EnqueueCallback callback);

  void RegisterEnqueue(Handler* handler, EnqueueCallback callback) override;

  // Unregister current EnqueueCallback from this queue, this will cause a crash if not registered yet.

  void UnregisterEnqueue();

  void UnregisterEnqueue() override;

  // Register |callback| that will be called on |handler| when the queue has at least one piece of data ready

  // for dequeue. This will cause a crash if handler or callback has already been registered before.

  void RegisterDequeue(Handler* handler, DequeueCallback callback);

  void RegisterDequeue(Handler* handler, DequeueCallback callback) override;

  // Unregister current DequeueCallback from this queue, this will cause a crash if not registered yet.

  void UnregisterDequeue();

  void UnregisterDequeue() override;

  // Try to dequeue an item from this queue. Return nullptr when there is nothing in the queue.

  std::unique_ptr<T> TryDequeue();

  std::unique_ptr<T> TryDequeue() override;

 private:

  void EnqueueCallbackInternal();