Custom Flow Controllers

Concept

A FlowController is the object responsible for shaping the network traffic by determining when attached asynchronous DataWriters are allowed to write data.

You can use one of the built-in FlowControllers (and optionally modify their properties), create a custom FlowController by using the DomainParticipant's create_flowcontroller() operation, or create a custom FlowController by using the DomainParticipant's PROPERTY QosPolicy (DDS Extension).

Example Description

This example shows how to create a custom flow controller to manage an asynchronous publisher.

In the 'Asynchronous Publishing' example we showed how asynchronous publication is useful to aggregate small messages into fewer packets, and thus achieve lower overhead. In this example we present another use case.

The publisher send a burst of large samples once per second. If many writers are sending in such bursts (particularly if synchronized), this will increase collisions, forcing resends in the case of reliable transmission, or causing data loss for best-effort transmissions. We use asynchronous publication with a custom flow controller to smooth out these bursts.

No changes are required on the subscriber, but we add a clock to show the effects of the FlowController.

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