DDS_SubscriptionMatchedStatus Struct Reference

DDS_SUBSCRIPTION_MATCHED_STATUS More...

Public Attributes
DDS_Long	total_count
	The total cumulative number of times that this DDSDataReader discovered a "match" with a DDSDataWriter.
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 DataWriters with which the DDSDataReader is matched.
DDS_Long	current_count_peak
	<<extension>> Greatest number of DataWriters that matched this DataReader 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_publication_handle
	This InstanceHandle can be used to look up which remote DDSDataWriter was the last to cause this DataReader's status to change, using DDSDataReader::get_matched_publication_data.

Detailed Description

DDS_SUBSCRIPTION_MATCHED_STATUS

A "match" happens when the DDSDataReader finds a DDSDataWriter with the same DDSTopic, same or compatible data type, and an offered QoS that is compatible with that requested by the DDSDataReader. (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 DDSDataReader will become "unmatched" from a remote DDSDataWriter when that DDSDataWriter goes away for any of the following reasons:

• The DDSDomainParticipant containing the matched DDSDataWriter has lost liveliness.

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

• The matched DataWriter has been deleted.

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

Note: A DataWriter's loss of liveliness (which is determined by DDS_LivelinessQosPolicyKind) does not trigger an unmatch event. So a DataWriter may still match even though its liveliness is lost.

Examples:

HelloWorld_subscriber.cxx.

Member Data Documentation

DDS_Long DDS_SubscriptionMatchedStatus::total_count

The total cumulative number of times that this DDSDataReader discovered a "match" with a DDSDataWriter.

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_SubscriptionMatchedStatus.

DDS_Long DDS_SubscriptionMatchedStatus::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 the DataReader ever matched with a DataWriter).

DDS_Long DDS_SubscriptionMatchedStatus::current_count

The current number of DataWriters with which the DDSDataReader 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_SubscriptionMatchedStatus.

DDS_Long DDS_SubscriptionMatchedStatus::current_count_peak

<<extension>> Greatest number of DataWriters that matched this DataReader simultaneously.

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

DDS_Long DDS_SubscriptionMatchedStatus::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 DataWriters have become unmatched for one or more of the reasons described in DDS_SubscriptionMatchedStatus.

DDS_InstanceHandle_t DDS_SubscriptionMatchedStatus::last_publication_handle

This InstanceHandle can be used to look up which remote DDSDataWriter was the last to cause this DataReader's status to change, using DDSDataReader::get_matched_publication_data.

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