text: /****************************************************************************
   *
   *   Copyright (c) 2019 PX4 Development Team. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name PX4 nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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   * POSSIBILITY OF SUCH DAMAGE.
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   ****************************************************************************/
  
  /**
   * @file SubscriptionCallback.hpp
   *
   */
  
  #pragma once
  
  #include <uORB/SubscriptionInterval.hpp>
  #include <containers/List.hpp>
  #include <px4_work_queue/WorkItem.hpp>
  
  namespace uORB
  {
  
  // Subscription wrapper class with callbacks on new publications
  class SubscriptionCallback : public SubscriptionInterval, public ListNode<SubscriptionCallback *>
  {
  public:
  	/**
  	 * Constructor
  	 *
  	 * @param meta The uORB metadata (usually from the ORB_ID() macro) for the topic.
  	 * @param instance The instance for multi sub.
  	 */
  	SubscriptionCallback(const orb_metadata *meta, uint8_t interval_ms = 0, uint8_t instance = 0) :
  		SubscriptionInterval(meta, interval_ms, instance)
  	{
  	}
  
  	virtual ~SubscriptionCallback()
  	{
  		unregister_callback();
  	};
  
  	bool register_callback()
  	{
  		bool ret = false;
  
  		if (_subscription.get_node() && _subscription.get_node()->register_callback(this)) {
  			// registered
  			ret = true;
  
  		} else {
  			// force topic creation by subscribing with old API
  			int fd = orb_subscribe_multi(_subscription.get_topic(), _subscription.get_instance());
  
  			// try to register callback again
  			if (_subscription.subscribe()) {
  				if (_subscription.get_node() && _subscription.get_node()->register_callback(this)) {
  					ret = true;
  				}
  			}
  
  			orb_unsubscribe(fd);
  		}
  
  
  		return ret;
  	}
  
  	void unregister_callback()
  	{
  		if (_subscription.get_node()) {
  			_subscription.get_node()->unregister_callback(this);
  		}
  	}
  
  	virtual void call() = 0;
  
  };
  
  // Subscription with callback that schedules a WorkItem
  class SubscriptionCallbackWorkItem : public SubscriptionCallback
  {
  public:
  	/**
  	 * Constructor
  	 *
  	 * @param work_item The WorkItem that will be scheduled immediately on new publications.
  	 * @param meta The uORB metadata (usually from the ORB_ID() macro) for the topic.
  	 * @param instance The instance for multi sub.
  	 */
  	SubscriptionCallbackWorkItem(px4::WorkItem *work_item, const orb_metadata *meta, uint8_t instance = 0) :
  		SubscriptionCallback(meta, 0, instance),	// interval 0
  		_work_item(work_item)
  	{
  	}
  
  	virtual ~SubscriptionCallbackWorkItem() = default;
  
  	void call() override
  	{
  		// schedule immediately if no interval, otherwise check time elapsed
  		if ((_interval_us == 0) || (hrt_elapsed_time(&_last_update) >= _interval_us)) {
  			_work_item->ScheduleNow();
  		}
  	}
  
  private:
  	px4::WorkItem *_work_item;
  };
  
  } // namespace uORB
  