PubSub+ API Concepts

In this section we'll provide you with an overview of PubSub+ messaging API fundamentals.


The PubSub+ APIs use processing Contexts for organizing communication between an application and a PubSub+ event broker. Contexts act as containers in which zero or more sessions are created and session-related events can be handled. A context encapsulates threads that drive network I/O and message delivery notification for the sessions and session components associated with that context. The life cycle of a context‑owned thread is bound to the life cycle of the Context.

A session can have zero or more:

  • flows

  • cache sessions

  • browsers

  • PubSub+ JCSMP API—One thread is used for I/O and another for notification.

  • PubSub+ Java RTO, C, and .NET APIs—A single thread is used for both I/O and for notification.

For more information, see Contexts.


A session creates a single, client connection to an event broker for sending and receiving messages. Sessions also allow applications to add and remove subscriptions.

A client can:

  • bind to endpoints to attract matching guaranteed messages (queues or topic endpoints).

  • publish messages to destinations (topics or queues).

  • add and remove subscriptions that attract messages with matching topics (topics). Subscriptions are also assigned to topic endpoints and optionally queue endpoints.

For more information, see Sessions.


A consumer flow is an API object that allows applications to receive guaranteed messages from an endpoint, such as a Queue. It is created by a session.

For more information, see Guaranteed Message Flows.