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An entity attached to a Subscriber, used to subscribe to a Topic, providing type-safe operations to read/receive data. Each Data Reader can be associated to only one Topic and therefore exactly one data type. This Topic must be created before the Data Reader. A data reader can obtain its subscribed data via two approaches:

• Listener-based approach, provides an asynchronous mechanism to obtain data via call-backs in a separate thread that does not block the main application.
• WaitSet-based Approach – A synchronous approach, blocks the current thread until one or more conditions attached to the WaitSet are met, at which point a list of active_conditions are returned.

There are several ways samples can be read using a data reader, this includes reading with conditions and some buffer management, described in greater detail in your respective language reference guide.

Source: OpenSplice Glossary