Plugins for the MADS network of distributed agents

This example project explores how to develop a plugin system for a C++ application. It is based on the pugg plugin system.

Building

To build the project, you need to have CMake installed. Then, you can run the following commands:

mkdir build
ccmake -Bbuild -DCMAKE_INSTALL_PREFIX=/usr/local
cmake --build build -j 8
sudo cmake --build build -t install

Plugins can be runtime loaded by MADS agents as mads-source, mads-filter, and mads-sink executables. The plugins are compiled as shared libraries, and they are installed in the <install prefix>/lib directory.

There can be three types of plugins: sources, filters, and sinks, suitable to be loaded by the corresponding MADS agents.

In the src/plugins directory there are three templates for the three types of plugins, plus some example plugins, such as echo, twice, and echoj.

Typically, each plugin code can contain a conditionally available main() function that can be used to test the plugin as a standalone executable. This is useful for debugging and testing the plugin before integrating it into the MADS framework. On MacOS, the plugin can be executed as a standalone executable, while on Linux and Windows, it can only be loaded by the corresponding agent executable. On the latter platforms, the plugin is also compiled as an executable that can be run directly. For example, the clock.cpp source is compiled on Linux and Windows as the library clock.plugin and the executable clock.

Plugin Versioning

The plugin system uses an internal version number Filter::version to check compatibility between the main application and the plugins. To invalidate a previously released plugin, simply imcrease the version number in the base class.

Implement new plugins

To create a new plugin, implement a derived class of Filter, Source or Sink by copying one of the templates.

Finally, create a new target in the src/plugin/CMakeLists.txt file that compiles the new plugin. Something like:

add_plugin(webcam SRCS other/possibly/needed/source.cpp LIBS LibsNeeded)

The main CMakeLists.txt file will automatically detect the new plugin and compile it. This file shall not be modified, unless you know what you're doing.

Authors

Paolo Bosetti (UniTN), with the help from Anna-Carla Araujo and Guillaume Cohen (INSA Toulouse)