Developing Apama Applications > Developing Apama Applications in EPL > Implementing Parallel Processing > Introduction to contexts > What is inside/outside a context?
What is inside/outside a context?
When you start a correlator it has a single main context. You can then create additional contexts. A context consists of the following:
*One or more monitor instances. Except, the main context exists even if it does not contain any monitor instances.
*An event input queue.
*Listeners that belong to the contained monitor instances.
The correlator maintains event definitions and monitor definitions outside contexts. This lets all contexts share the same event and monitor definitions.
Instances of the same monitor can exist in multiple contexts. Each monitor instance belongs to a single context. For example, suppose you inject monitor A. Monitor A spawns within its own context (the main context) twice and spawns once to the alpha context. This creates three additional monitor instances. Two instances are in the main context and one instance is in the alpha context. These instances do not share any data, other than by means of passing events.
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