Multiple thread acess same uorb toptic

When I read the code,I find there are some thread which access the same uorb topic,
that is not advertised and subscribed with the function orb_advertise_multi and orb_subscribe_multi.
So I read the the uorb modules,the read function of uorb topic is:

uORB::DeviceNode::read(struct file *filp, char *buffer, size_t buflen)
SubscriberData *sd = (SubscriberData *)filp_to_sd(filp);

/* if the object has not been written yet, return zero */
if (_data == nullptr) {
	return 0;

/* if the caller's buffer is the wrong size, that's an error */
if (buflen != _meta->o_size) {
	return -EIO;

 * Perform an atomic copy & state update
irqstate_t flags = px4_enter_critical_section();

if (_generation > sd->generation + _queue_size) {
	/* Reader is too far behind: some messages are lost */
	_lost_messages += _generation - (sd->generation + _queue_size);
	sd->generation = _generation - _queue_size;

if (_generation == sd->generation && sd->generation > 0) {
	/* The subscriber already read the latest message, but nothing new was published yet.
	 * Return the previous message

/* if the caller doesn't want the data, don't give it to them */
if (nullptr != buffer) {
	memcpy(buffer, _data + (_meta->o_size * (sd->generation % _queue_size)), _meta->o_size);

if (sd->generation < _generation) {

/* set priority */

 * Clear the flag that indicates that an update has been reported, as
 * we have just collected it.


return _meta->o_size;


As the description of above code,Multiple thread can read the same topic even if I don’t use orb_advertise_multi and orb_subscribe_multi. Am I correct?

The multi versions are for multiple instances of the same topic. For example all gyros publish sensor_gyro, but then there’s instance 0, 1, 2, etc.

Hi ,dagar!
I know what you say.Your example for gyros publish with instance 0, 1, 2 exactly are not the same device node.
What I say is that you can use single version advertise and use single subscribe in multiple thread to get the newest data.

Yes multiple readers of the same advertised topic is not a problem. Each is its own subscription. My point was that multi is a separate topic.