Subscription.cpp

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/**
 * @file Subscription.cpp
 *
 */

#include "Subscription.hpp"
#include <px4_platform_common/defines.h>

namespace uORB
{

bool
Subscription::subscribe()
{
    // valid ORB_ID required
    if (_meta == nullptr) {
        return false;
    }

    // check if already subscribed
    if (_node != nullptr) {
        return true;
    }

    DeviceMaster *device_master = uORB::Manager::get_instance()->get_device_master();

    if (device_master != nullptr) {
        uORB::DeviceNode *node = device_master->getDeviceNode(_meta, _instance);

        if (node != nullptr) {
            _node = node;
            _node->add_internal_subscriber();

            // If there were any previous publications, allow the subscriber to read them
            const unsigned curr_gen = _node->published_message_count();
            const uint8_t q_size = _node->get_queue_size();

            if (q_size < curr_gen) {
                _last_generation = curr_gen - q_size;

            } else {
                _last_generation = 0;
            }

            return true;
        }
    }

    return false;
}

void
Subscription::unsubscribe()
{
    if (_node != nullptr) {
        _node->remove_internal_subscriber();
    }

    _node = nullptr;
    _last_generation = 0;
}

bool
Subscription::init()
{
    if (_meta != nullptr) {
        // this throttles the relatively expensive calls to getDeviceNode()
        if ((_last_generation == 0) || (_last_generation < 1000) || (_last_generation % 100 == 0))  {
            if (subscribe()) {
                return true;
            }
        }

        if (_node == nullptr) {
            // use generation to count attempts to subscribe
            _last_generation++;
        }
    }

    return false;
}

bool
Subscription::update(uint64_t *time, void *dst)
{
    if ((time != nullptr) && (dst != nullptr) && advertised()) {
        // always copy data to dst regardless of update
        const uint64_t t = _node->copy_and_get_timestamp(dst, _last_generation);

        if (*time == 0 || *time != t) {
            *time = t;
            return true;
        }
    }

    return false;
}

} // namespace uORB