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A Condition is an object attached to a WaitSet which allows a thread to block until one or more of the attached condition objects evaluates to true or until the timeout occurs. Each Condition has a trigger_value that can be true or false and is set by the Data Distribution Service. Conditions can be of type:

• Guard Condition
  Application controlled, unblocks a WaitSet manually by triggering the GuardCondition set_trigger_value(TRUE).
• Status Condition
  Provides a generic mechanism for the application to be informed about relevant communication status conditions from Entity objects that have status attributes, access is provided to the application by the get_statuscondition operation. The available status’ depend on the Entity and are described in your relevant language reference guide.
• Read Condition
  Allows an application to specify the data samples it is interested in by means of their lifecycle states. The WaitSet triggers as long as data is available that matches the selected SampleState, ViewState and
• Query Condition
  Allows an application to specify the data samples it is interested in by means of an SQL-expression.

Source: OpenSplice Glossary