Method Dequeue

be/src/util/internal-queue.h:132–150

Dequeues an element from the queue's head. Returns nullptr if the queue is empty. This is O(1).

  /// Dequeues an element from the queue's head. Returns nullptr if the queue
  /// is empty. This is O(1).
  T* Dequeue() {
    Node* result = nullptr;
    {
      std::lock_guard<LockType> lock(lock_);
      if (IsEmptyLocked()) return nullptr;
      --size_;
      result = head_;
      head_ = head_->next;
      if (head_ == nullptr) {
        tail_ = nullptr;
      } else {
        head_->prev = nullptr;
      }
    }
    DCHECK(result != nullptr);
    result->next = result->prev = nullptr;
    result->parent_queue = nullptr;
    return reinterpret_cast<T*>(result);
  }

  /// Dequeues an element from the queue's tail. Returns nullptr if the queue
  /// is empty. This is O(1).