Subscription Module

Class model of the DCPS Subscription Module

The Subscription Module is comprised of the following classifiers:

• Subscriber
• DataReader
• DataSample
• SampleInfo
• Subscriber Listener
• DataReader Listener
• Read Condition
• Query Condition

The Subscriber

The Subscriber is responsible for collecting data from various publications:

• Each datatype must be accessed using its own typed DataReader.
• A DataReader gives access to samples and their corresponding SampleInfo.
• SampleInfo describes relevant information about the state of a sample and the instance to which it relates, for example about its lifecycle.
• The Subscriber acts as a factory for typed DataReaders.
• DataReaders do not read their data directly from the network:
  • it is the Subscriber that decides when and how the data is transmitted to its DataReaders:
• Groups of messages (possibly coming from different DataWriters) can be received as a whole, allowing for a sort of transaction. (See PresentationQoSPolicy).
• A Subscriber only collects samples that are published in the selected Partitions (See Partition QoS PartitionQosPolicy.)

Applicable QoS

QoS	Brief
GROUP_DATA	User data
ENTITY_FACTORY	Auto enable/disable entities on creation
PRESENTATION	Specifies how the samples representing changes to the data instances are presented
PARTITION	Set of strings that represent the logical partition among topics
SHARE	Used to share a Subscriber between multiple processes.

Default QoS Values

QoS	Attribute	Value
GROUP_DATA	value.length	0
ENTITY_FACTORY	autoenable_created_entities	TRUE
PRESENTATION	access_scope coherent_access ordered_access	INSTANCE FALSE FALSE
PARTITION	name.length	0
SHARE	name enable	NULL FALSE

Related Status Conditions

Status	Brief
DATA_ON_READERS	New information is available

Related Listeners

Listener	Brief
on_data_on_readers()	Data available on one of the attached DataReaders