DDS_PublicationMatchedStatus Struct Reference

DDS_PUBLICATION_MATCHED_STATUS More...

Data Fields
DDS_Long	total_count
	The total cumulative number of times that this DDS_DataWriter discovered a "match" with a DDS_DataReader.
DDS_Long	total_count_change
	The changes in total_count since the last time the listener was called or the status was read.
DDS_Long	current_count
	The current number of DataReaders with which this DDS_DataWriter is matched.
DDS_Long	current_count_peak
	<<extension>> Greatest number of DataReaders that matched this DDS_DataWriter simultaneously.
DDS_Long	current_count_change
	The change in current_count since the last time the listener was called or the status was read.
DDS_InstanceHandle_t	last_subscription_handle
	This InstanceHandle can be used to look up which remote DDS_DataReader was the last to cause this DataWriter's status to change, using DDS_DataWriter_get_matched_subscription_data.

Detailed Description

DDS_PUBLICATION_MATCHED_STATUS

A "match" happens when the DDS_DataWriter finds a DDS_DataReader with the same DDS_Topic, same or compatible data type, and requested QoS that is compatible with that offered by the DDS_DataWriter. (For information on compatible data types, see the Getting Started Guide, Addendum for Extensible Types .)

This status is also changed (and the listener, if any, called) when a match is ended. A local DDS_DataWriter will become "unmatched" from a remote DDS_DataReader when that DDS_DataReader goes away for any of the following reasons:

• The matched DDS_DataReader's DDS_DomainParticipant has lost liveliness.

• This DataWriter or the matched DataReader has changed QoS such that the entities are now incompatible.

• The matched DataReader has been deleted.

This status may reflect changes from multiple match or unmatch events, and the DDS_PublicationMatchedStatus::current_count_change can be used to determine the number of changes since the listener was called back or the status was checked.

Field Documentation

DDS_Long DDS_PublicationMatchedStatus::total_count

The total cumulative number of times that this DDS_DataWriter discovered a "match" with a DDS_DataReader.

This number increases whenever a new match is discovered. It does not decrease when an existing match goes away for any of the reasons described in DDS_PublicationMatchedStatus.

DDS_Long DDS_PublicationMatchedStatus::total_count_change

The changes in total_count since the last time the listener was called or the status was read.

Note that this number will never be negative (because it's the total number of times this DataWriter ever matched with a DataReader).

DDS_Long DDS_PublicationMatchedStatus::current_count

The current number of DataReaders with which this DDS_DataWriter is matched.

This number increases when a new match is discovered and decreases when an existing match goes away for any of the reasons described in DDS_PublicationMatchedStatus.

DDS_Long DDS_PublicationMatchedStatus::current_count_peak

<<extension>> Greatest number of DataReaders that matched this DDS_DataWriter simultaneously.

That is, there was no moment in time when more than this many DataReaders matched this DataWriter. (As a result, total_count can be higher than current_count_peak.)

DDS_Long DDS_PublicationMatchedStatus::current_count_change

The change in current_count since the last time the listener was called or the status was read.

Note that a negative current_count_change means that one or more DataReaders have become unmatched for one or more of the reasons described in DDS_PublicationMatchedStatus.

DDS_InstanceHandle_t DDS_PublicationMatchedStatus::last_subscription_handle

This InstanceHandle can be used to look up which remote DDS_DataReader was the last to cause this DataWriter's status to change, using DDS_DataWriter_get_matched_subscription_data.

If the DataReader no longer matches this DataWriter due to any of the reasons in DDS_PublicationMatchedStatus except incompatible QoS, then the DataReader has been purged from this DataWriter's DomainParticipant discovery database. (See the "What is Discovery?" section of the User's Manual.) In that case, the DDS_DataWriter_get_matched_subscription_data method will not be able to return information about the DataReader. The only way to get information about the lost DataReader is if you cached the information previously.