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1. Developing new features

1.1. Developing new Addons


GEMOC addons mecanism is the simpliest way to contribute new features to GEMOC. Most of the features in GEMOC have been developed using it.

Basically, it uses Eclipse plugin extension point in order to provide additional feature to an existing engine.

The main extension point is org.eclipse.gemoc.gemoc_language_workbench.engine_addon which allows to declare a new class that implements the IEngineAddon interface.

1.1.1. Create an Addon

Minimal steps to get an addons:

  • Create a plugin project (or contribute to an existing one)
  • In the MANIFEST.MF or plugin.xml editor, open the extensions tab, Add, uncheck "Show only extension from the required plugins", search for "gemoc" and select the org.eclipse.gemoc.gemoc_language_workbench.engine_addon extension point, accept to add the dependency to the plugin. (see Figure 61, “New Extension for Engine Addon screenshot”)
  • add an addon entry in the extension point (see Figure 62, “EngineAddon extension point details screenshot”) provide a name and a description that will help the end user to know if she wish to enable the addon or not in the launch tab when configuring her model execution.
  • Create the class implementing org.eclipse.gemoc.xdsmlframework.api.engine_addon.IEngineAddon (a click on Class*: in the extension editor allows to open a wizard that simplify this task)
  • you can now override any of the default methods of the interface (cf. Figure 57, “Execution Framework API Interfaces overview”). If the user select the addon in the launch tab, these methods will be called by the engine.
New Extension forEngine Addon screenshot

Figure 61. New Extension for Engine Addon screenshot

EngineAddon extension point details screenshot

Figure 62. EngineAddon extension point details screenshot


An Engine addon may be generic and apply to any language, but it can also be language specific. In that case, you should prefer to add its code in the project containing the dsl file of the language and declare it in the plugin.xml.

This way, the addon will be available only for this specific language.

Add language specific Engine Addon on DSL

Figure 63. Add language specific Engine Addon on DSL

This can be useful in order to create language specific GUI (with input/output) and complex model animation. (see Section 3.2, “Define an animation representation using an engine addon”)


In the extension declaration, setting Default to true will activate the addon by default when creating a new launch configuration. The user is still able to disable the addon manually.

1.1.2. Controling call to addon


The calls from the engine to the methods of IEngineAddons block the model execution. Thus, except if this is the expected behavior, the addons should avoid to do complex/long running/blocking task directly in the

For a given notification to IEngineAddon (for example aboutToExecuteStep), the order of calls to all registered addons is by default not ensured.

However, an addon can declare some EngineAddonSortingRule in order to indicate if the addon mus be called before or after another addon for a given EngineEvent.

The other addon can be identified either via its id or any tag that has been associated to it.


When starting a model execution the console logs some informations about which addon has been enabled and when each addon will be called compared to other addons.

The implicit GemocDebug addon is in charge to lock the execution when it receives a pause command. Addons that displays some information on the UI may wish to be called before it in order to make sure to provide updated information.

This snippet show how to add a rule that enforce this.

public class MyAddon implements IEngineAddon {

	public void aboutToExecuteStep(IExecutionEngine<?> engine, Step<?> logicalStepToApply) {
		// do some refresh action

	public List<EngineAddonSortingRule> getAddonSortingRules() {  1
		ArrayList<EngineAddonSortingRule> sortingRules = new ArrayList<EngineAddonSortingRule>();
		sortingRules.add(new EngineAddonSortingRule( this,
				Arrays.asList(IGemocDebugger.GROUP_TAG))); 2
		return sortingRules;


create a rule to ensure good behavior with GemocDebugger. The debugger addon will stop the execution in this event, this make sure to be called before it in order to properly do the task (refresh the view, save info, etc)


use the group tag so this rule will work with any GemocDebugger implementation.


See Section 3, “GEMOC framework” for more details about the extension point and other supported features.

1.2. Developing new engines


As seen in Figure 49, “Components overview”, the framework is organized in several layers. The most complete layer is the GEMOC Framework which offers most of the advanced features. Thus, implementing an engine for a new technology consist in 2 main parts:

  • implementing subclasses for the classes from XDSML Framework in order to have the part dedicated to the Language Workbench,
  • and implementing subclasses for the classes from Execution Framework in order to have the part dedicated to the Modeling Workbench

2. Distributing new features

TODO add info about how to distribute contribution and new features

3. Documentation


The GEMOC documentation (this document) structure is designed to:

  • allow both online and eclipse help output,
  • display an outline that helps organizing contributions,
  • maintain the documentation sources as close as possible of the documented element in order to associate documentation commits to the code commits,
  • use a rich but human readable syntax,
  • ease modification.

As it supports include directives, we chose Asciidoc syntax with the appropriate tool chain.

Some of the diagrams are generated using plantuml.

The document is organized as follow:


In order to ease modifications, every files must start with a footnote allowing to retrieve the source file in the git repositories.


To edit the documentation we recommand the use of plantuml eclipse plugin and eclipse asciidoc editor . You can install them in an Eclipse using either the market place or the following update site: