===== Data Reader =====
[[dido:public:ra:xapend:xapend.a_glossary:start| Return to Glossary ]]

An [[dido:public:ra:xapend:xapend.a_glossary:e:entity|entity]] attached to a [[dido:public:ra:xapend:xapend.a_glossary:s:subscriber|Subscriber]], used to subscribe to a [[dido:public:ra:xapend:xapend.a_glossary:t:topic|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:

  * [[dido:public:ra:xapend:xapend.a_glossary:l:listener|Listener]]-based approach, provides an asynchronous mechanism to obtain data via call-backs in a separate thread that does not block the main [[dido:public:ra:xapend:xapend.a_glossary:a:application|application]].
  * WaitSet-based Approach – A synchronous approach, blocks the current thread until one or more conditions attached to the [[dido:public:ra:xapend:xapend.a_glossary:w:waitset|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: [[https://istkb.adlinktech.com/article/vortex-opensplice-dds-glossary/ | OpenSplice Glossary]]