PX4-Autopilot/platforms/common/uORB/SubscriptionCallback.hpp

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/**
 * @file SubscriptionCallback.hpp
 *
 */

#pragma once

#include <uORB/SubscriptionInterval.hpp>
#include <containers/List.hpp>
#include <px4_platform_common/px4_work_queue/WorkItem.hpp>
#include <drivers/drv_hrt.h>

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 interval_us The requested maximum update interval in microseconds.
	 * @param instance The instance for multi sub.
	 */
	SubscriptionCallback(const orb_metadata *meta, uint32_t interval_us = 0, uint8_t instance = 0) :
		SubscriptionInterval(meta, interval_us, instance)
	{
	}

	virtual ~SubscriptionCallback()
	{
		unregisterCallback();
	};

	bool registerCallback();

	void unregisterCallback();

	/**
	 * Change subscription instance
	 * @param instance The new multi-Subscription instance
	 */
	bool ChangeInstance(uint8_t instance)
	{
		bool ret = false;

		if (instance != get_instance()) {
			const bool registered = _registered;

			if (registered) {
				unregisterCallback();
			}

			if (_subscription.ChangeInstance(instance)) {
				ret = true;
			}

			if (registered) {
				registerCallback();
			}

		} else {
			// already on desired index
			return true;
		}

		return ret;
	}

	virtual void call(unsigned generation) = 0;

	bool registered() const { return _registered; }

protected:

	bool _registered{false};
	// Node generation at our last ScheduleNow(), used by the count gate. Only ever
	// touched from call() (which runs under the publishing node's lock, so it is
	// serialized) - do NOT write it from the subscriber thread (e.g. in
	// registerCallback()), or it becomes a cross-thread race. It self-initializes:
	// the first call() sees a large delta and schedules once, then tracks normally.
	unsigned _last_scheduled_generation{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(unsigned generation) override
	{
		// 'generation' is the publishing node's generation, handed in by the
		// publisher - so unlike before we never read the subscriber's own cursor
		// (_last_generation, mutated on the subscriber's thread) from here.
		// Schedule once enough new samples have accrued since our last schedule
		// (count gate), respecting the optional interval (interval gate).
		const uint8_t req = _required_updates.load();

		if ((generation - _last_scheduled_generation) >= req) {
			const hrt_abstime last_update = _last_update.load();

			if ((_interval_us == 0) || (hrt_elapsed_time(&last_update) >= _interval_us)) {
				_last_scheduled_generation = generation;
				_work_item->ScheduleNow();
			}
		}
	}

	/**
	 * Optionally limit callback until more samples are available.
	 *
	 * @param required_updates Number of queued updates required before a callback can be called.
	 */
	void set_required_updates(uint8_t required_updates)
	{
		// TODO: constrain to queue depth?
		_required_updates.store(required_updates);
	}

private:
	px4::WorkItem *_work_item;

	px4::atomic<uint8_t> _required_updates{0};
};

} // namespace uORB