text: // Copyright 2016 Proyectos y Sistemas de Mantenimiento SL (eProsima).
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #ifndef _RTPS_RESOURCES_ASYNC_INTEREST_TREE_H_
  #define _RTPS_RESOURCES_ASYNC_INTEREST_TREE_H_
  
  #include <fastrtps/rtps/writer/RTPSWriter.h>
  #include <mutex>
  #include <set>
  
  namespace eprosima {
  namespace fastrtps{
  namespace rtps {
  
  /*!
   * Used by AsyncWriterThread to manage a double queue.
   * One queue is being processed by AsyncWriterThread's internal thread while in the other one other threads can register
   * RTPSWriter pointers that need to send samples asynchronously.
   */
  class AsyncInterestTree
  {
      friend class AsyncWriterThread;
  
      public:
  
      /*!
       * @brief Registers a writer in a hidden queue.
       * @param writer Pointer to the writer.
       * @return true if the writer was queued or false if it already is queued.
       */
      bool register_interest(
              RTPSWriter* writer);
  
      /*!
       * @brief Registers a writer in a hidden queue.
       * @param writer Pointer to the writer.
       * @param max_blocking_time Time point until the function must be blocked.
       * @return true if the writer was queued or false if it already is queued.
       * @note This method is blocked for a period of time.
       */
      bool register_interest(
              RTPSWriter* writer,
              const std::chrono::time_point<std::chrono::steady_clock>& max_blocking_time);
  
      /*!
       * @brief Unregister a writer from both queues.
       * @param writer Pointer to the writer.
       * @return true if both queues remain empty.
       */
      bool unregister_interest(
              RTPSWriter* writer);
  
      /*!
       * @brief Clears the visible queue and swaps with the hidden set.
       */
      void swap();
  
      /*!
       * @brief Remove next writer from visible queue and returns it.
       * @return Next writer.
       */
      RTPSWriter* next_active_nts();
  
      private:
  
      bool register_interest_nts(
              RTPSWriter* writer);
  
      mutable std::timed_mutex mMutexActive, mMutexHidden;
  
      RTPSWriter* active_front_ = nullptr;
  
      RTPSWriter* hidden_front_ = nullptr;
  
      int active_pos_ = 0;
  
      int hidden_pos_ = 1;
  };
  
  } /* namespace rtps */
  } /* namespace fastrtps */
  } /* namespace eprosima */
  
  #endif // _RTPS_RESOURCES_ASYNC_INTEREST_TREE_H_
  