30. Publishers

An application that intends to publish information needs the following Entities: DomainParticipant, Topic, Publisher, and DataWriter. All Entities have a corresponding specialized Listener and a set of QosPolicies. A Listener is how Connext notifies your application of status changes relevant to the Entity. The QosPolicies allow your application to configure the behavior and resources of the Entity.

A DomainParticipant defines the DDS domain in which the information will be made available.
A Topic defines the name under which the data will be published, as well as the type (format) of the data itself.
An application writes data using a DataWriter. The DataWriter is bound at creation time to a Topic, thus specifying the name under which the DataWriter will publish the data and the type associated with the data. The application uses the DataWriter’s write() operation to indicate that a new value of the data is available for dissemination.
A Publisher manages the activities of several DataWriters. The Publisher determines when the data is actually sent to other applications. Depending on the settings of various QosPolicies of the Publisher and DataWriter, data may be buffered to be sent with the data of other DataWriters or not sent at all. By default, the data is sent as soon as the DataWriter’s write() function is called.

You may have multiple Publishers, each managing a different set of DataWriters, or you may choose to use one Publisher for all your DataWriters.

For more information, see 30.1 Creating Publishers Explicitly vs. Implicitly.

Figure 30.1: Publication Module shows how these Entities are related, as well as the methods defined for each Entity.

Figure 30.1: Publication Module

Publishers are used to perform the operations listed in Table 30.1 Publisher Operations. You can find more information about the operations by looking in the section listed under the Reference column. For details such as formal parameters and return codes, please see the API Reference HTML documentation.

Some operations cannot be used within a listener callback, see 15.8.8.1 Restricted Operations in Listener Callbacks.

Table 30.1 Publisher Operations
Working with ...	Operation	Description	Reference
DataWriters	begin_coherent_ changes	Indicates that the application will begin a coherent set of modifications.	31.10 Writing Coherent Sets of DDS Data Samples
	create_datawriter	Creates a DataWriter that will belong to the Publisher.	31.1 Creating DataWriters
	create_datawriter_ with_profile	Sets the DataWriter’s QoS based on a specified QoS profile.	31.1 Creating DataWriters
	copy_from_topic_qos	Copies relevant QosPolicies from a Topic into a DataWriterQoS structure.	30.4.6 Other Publisher QoS-Related Operations
DataWriters cont'd	delete_contained_ entities	Deletes all of the DataWriters that were created by the Publisher.	30.3.1 Deleting Contained DataWriters
	delete_datawriter	Deletes a DataWriter that belongs to the Publisher.	31.3 Deleting DataWriters
	end_coherent_changes	Ends the coherent set initiated by begin_coherent_changes().	31.10 Writing Coherent Sets of DDS Data Samples
DataWriters cont'd	get_all_datawriters	Retrieves all the DataWriters created from this Publisher.	31.2 Getting All DataWriters
	get_default_ datawriter_qos	Copies the Publisher’s default DataWriterQoS values into a DataWriterQos structure.	31.15 Setting DataWriter QosPolicies
	get_status_changes	Will always return 0 since there are no Statuses currently defined for Publishers.	15.4 Getting Status and Status Changes
	lookup_datawriter	Retrieves a DataWriter previously created for a specific Topic.	30.6 Finding a Publisher’s Related DDS Entities
DataWriters cont'd	set_default_datawriter_qos	Sets or changes the default DataWriterQos values.	30.4.5 Getting and Setting Default QoS for DataWriters
	set_default_datawriter_ qos_with_profile	Sets or changes the default DataWriterQos values based on a QoS profile.	30.4.5 Getting and Setting Default QoS for DataWriters
	wait_for_ acknowledgments	Blocks until all data written by the Publisher’s reliable DataWriters are acknowledged by all matched reliable DataReaders, or until the a specified timeout duration, max_wait, elapses.	30.7 Waiting for Acknowledgments in a Publisher
	is_sample_app_acknowledged	Indicates if a sample has been application-acknowledged by all the matching DataReaders that were alive when the sample was written. If a DataReader does not enable application acknowledgment (by setting the ReliabilityQosPolicy's acknowledgment_kind to a value other than DDS_PROTOCOL_ACKNOWLEDGMENT_MODE), the sample is considered application-acknowledged for that DataReader.	31.12 Application Acknowledgment
Libraries and Profiles	get_default_library	Gets the Publisher’s default QoS profile library.	30.4.4 Getting and Setting the Publisher’s Default QoS Profile and Library
	get_default_profile	Gets the Publisher’s default QoS profile.
	get_default_profile_ library	Gets the library that contains the Publisher’s default QoS profile.
	set_default_library	Sets the default library for a Publisher.
	set_default_profile	Sets the default profile for a Publisher.
Participants	get_participant	Gets the DomainParticipant that was used to create the Publisher.	30.6 Finding a Publisher’s Related DDS Entities
Publishers	enable	Enables the Publisher.	15.2 Enabling DDS Entities
	equals	Compares two Publisher’s QoS structures for equality.	30.4.2 Comparing QoS Values
	get_qos	Gets the Publisher’s current QosPolicy settings. This is most often used in preparation for calling set_qos().	30.4 Setting Publisher QosPolicies
	set_qos	Sets the Publisher’s QoS. You can use this operation to change the values for the Publisher’s QosPolicies. Note, however, that not all QosPolicies can be changed after the Publisher has been created.
	set_qos_with_profile	Sets the Publisher’s QoS based on a specified QoS profile.
Publishers cont'd	get_listener	Gets the currently installed Listener.	30.5 Setting Up PublisherListeners
	set_listener	Sets the Publisher’s Listener. If you created the Publisher without a Listener, you can use this operation to add one later.	30.5 Setting Up PublisherListeners
	suspend_publications	Provides a hint that multiple data-objects within the Publisher are about to be written.Connext does not currently use this hint.	30.9 Suspending and Resuming Publications
	resume_publications	Reverses the action of suspend_publications().	30.9 Suspending and Resuming Publications