Inter-transport Communication

Inter-transport communication becomes necessary, when participants want to communicate that are connected to the unified bus using different transport mechanisms.

Note

This description describes the TCP-based transport but also applies to the Spread transport.

Inter-Transport Setup

This page describes how to setup participants for inter-transport communication using the following scenario which is illustrated in the above figure:

Participants reside in two separate processes

• One process is an instance of the program inprocess-and-socket (source: inprocess-and-socket.cpp)

  • There is one informer in the process. It has two connectors

    • One connector for the Spread transport

    • One connector for the inprocess transport

  • There is one listener in the process. It has two connectors

    • One connector for the Spread transport

    • One connector for the inprocess transport

• The other process is an instance of the program socket-only (source: socket-only.cpp)

  • There is one listener in the process. It has a single connector for the Spread transport.

Note

With this setup, the listener in the inprocess-and-socket process will currently receive all events twice.

There are two ways to attach multiple transports to participants:

1. Via configuration options (configuration file, environment variables, etc.)

2. Programmatically

These two alternatives are described below.

Via Configuration Options

When configured via the configuration mechanism, the multi-transport setup will have a global effect in the following sense: it will affect all participants in all processes which are not explicitly instantiated with a different set of connectors.

In addition to the Spread transport which is (currently) enabled by default, other transports can be enabled globally using a configuration file fragment like this:

[transport.inprocess]
enabled = 1

Programmatically (C++)

The set of transports used by individual participants or as a default by all newly created participants can be configured by modifying rsb::ParticipantConfig::Transport objects. These objects contain, among other things, an option which controls whether a particular transport is enabled. A modified rsb::ParticipantConfig object can be used in two ways:

Globally for a Process

The example programs inprocess-and-socket.cpp and socket-only.cpp implement the inter-transport setup described above by modifying the default participant configuration in the inprocess-and-socket process to include the inprocess transport.

Locally for a Participant

In order to use a prepared rsb::ParticipantConfig object only locally instead of installing it as a global default, it can be passed to the following methods:

• rsb::Factory::createReader

• rsb::Factory::createListener

• rsb::Factory::createInformer

Note

In each of these cases, the modified configuration options will only effect the participant created by the method call.