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Capsule Factory

A capsule factory is responsible for creating and destroying instances of a capsule. The TargetRTS has a default capsule factory which implements the default rules for capsule instance creation and destruction in a capsule part. These rules are:

  1. A capsule instance is created using the new operator and destroyed using the delete operator.
  2. The default capsule constructor is used when creating the instance, i.e. the constructor that just takes the two mandatory parameters.
  3. A capsule instance is run by the same thread (i.e. RTController) as runs the container capsule instance (unless a specific thread is provided).
  4. A capsule instance is inserted into the first free index of the capsule part (unless a specific index is provided).
  5. The type of the capsule part is used for deciding the dynamic type of the created capsule instance (unless a specific capsule type is provided).

When you incarnate a capsule into an optional part using the incarnate() functions of a Frame port, you can customize rules 3, 4 and 5 above by using different overloads of incarnate(). However, if you want to customize rules 1 and/or 2, or incarnate a fixed part, you need to provide your own capsule factory. This can be done in a few different ways.

Local Capsule Factory

You can provide a local capsule factory for a part by implementing the rt::create and/or rt::destroy code snippets. For an example see Part with Capsule Factory.

You can also provide a local capsule factory in a more dynamic way when you incarnate an optional part by calling incarnateCustom() instead of incarnate(). For an example see Capsule Constructor. However, note that in this case it's only possible to provide the create implementation of the capsule factory, and capsule instances created that way will always be deleted using the delete operator.

Scenarios where a local capsule factory could be useful include:

  • Providing arguments for a custom capsule constructor when creating a capsule instance.
  • Creating a capsule instance in a fixed part and let it be run by a different thread than what runs the container capsule instance.
  • Incarnate a fixed part by creating an instance of a capsule that inherits from the capsule that types the part.


You can find a sample application that uses a local capsule factory here.

Global Capsule Factory

A global capsule factory will be used for creating and destroying capsule instances in all capsule parts in the application, except those for which a local capsule factory has been provided. Implement a global capsule factory by means of a class that inherits RTActorFactoryInterface. You need to implement the create() and destroy() functions. Then define an object of this class and set the capsuleFactory TC property to the address of that object.

Here is an example of how a global capsule factory can be implemented in an Art file called

class CapsuleFactory : public RTActorFactoryInterface {
    RTActor *create(RTController *rts, RTActorRef *ref, int index) override {

        // Create capsule instance here

    void destroy(RTActor* actor) override {
        // Delete capsule instance here

    static CapsuleFactory factory;

CapsuleFactory CapsuleFactory::factory;

In the TC, specify the capsule factory object and make sure the capsule factory header file gets included everywhere:

tc.capsuleFactory = "&CapsuleFactory::factory";
tc.commonPreface = `
#include ""

If the expression specified in the capsuleFactory property contains the variable $(CAPSULE_CLASS) it will be replaced with the name of the C++ class that is generated for the capsule. This can be useful for implementing a generic capsule factory which takes the capsule class as a template parameter.

Scenarios where a global capsule factory could be useful include:

  • Allocating capsule instances in a memory pool by using the placement new operator.
  • Logging capsule instance creation and destruction.
  • Customizing creation of certain capsule instances by means of dependency injection.


You can find a sample application that uses a global capsule factory here.