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specification-inter-transport-communication.rst

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Inter-transport Communication

Inter-:term:`transport` communication becomes necessary, when :term:`participants <participant>` want to communicate that are connected to the unified bus using different :term:`transport` mechanisms.

Note

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

Inter-Transport Setup

.. digraph:: interTransport

   resolution=60

   subgraph clusterInprocessAndSocket {
     label="inprocess-and-socket : Process"

     l1 [label="Listener", shape=box, style=filled, fillcolor="#c0ffc0"]
     sic1 [label="Socket In Connector", shape=octagon, style=filled, fillcolor="#ffc0c0"]
     iic1 [label="Inprocess In Connector", shape=octagon, style=filled, fillcolor="#ffc0c0"]

     sic1 -> l1
     iic1 -> l1

     i1 [label="Informer", shape=box, style=filled, fillcolor="#c0ffc0"]
     soc1 [label="Socket Out Connector", shape=octagon, style=filled, fillcolor="#ffc0c0"]
     ioc1 [label="Inprocess Out Connector", shape=octagon, style=filled, fillcolor="#ffc0c0"]

     i1 -> soc1
     i1 -> ioc1

     ib [label="Inprocess Bus", shape=ellipse, style=filled, fillcolor="#c0c0ff"]

     ib -> iic1
     ioc1 -> ib
   }

   subgraph clusterSocketOnly {
     label="socket-only : Process"

     l2 [label="Listener", shape=box, style=filled, fillcolor="#c0ffc0"]
     sic2 [label="Socket In Connector", shape=octagon, style=filled, fillcolor="#ffc0c0"]

     sic2 -> l2
   }

   sb [label="Socket Bus", shape=ellipse, style=filled, fillcolor="#c0c0ff"]

   sb -> sic1
   soc1 -> sb
   sb -> sic2

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

:term:`Participants <participant>` reside in two separate processes

Note

With this setup, the :term:`listener` in the :program:`inprocess-and-socket` process will currently receive all :term:`events <event>` twice.

There are two ways to attach multiple :term:`transports <transport>` to :term:`participants <participant>`:

  1. Via :ref:`configuration options <configuration>` (:ref:`configuration file <specification-config-files>`, :ref:`environment variables <specification-config-environment-variables>`, etc.)
  2. Programmatically

These two alternatives are described below.

Via Configuration Options

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

In addition to the :term:`Spread` :term:`transport` which is (currently) enabled by default, other :term:`transports <transport>` can be enabled globally using a :ref:`configuration file <specification-config-files>` fragment like this:

[transport.inprocess]
enabled = 1

Programmatically (C++)

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

Globally for a Process

The example programs :download:`inprocess-and-socket.cpp <upstream/rsb-cpp/examples/inter_transport/inprocess-and-socket.cpp>` and :download:`socket-only.cpp <upstream/rsb-cpp/examples/inter_transport/socket-only.cpp>` implement the inter-:term:`transport` setup described above by modifying the default :term:`participant` configuration in the :program:`inprocess-and-socket` process to include the :term:`inprocess` :term:`transport`.

Locally for a :term:`Participant`

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

Note

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