Understanding Activation Groups

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An Activation Group is a substructure of a Job that serves to control the state of groups of programs. The Activation Group keeps a reference for each program that belongs to it.

Before a program is given execution control, the program’s activation instance has to be found or created; if an adequate activation exists in the Job it is used, otherwise, the program must be activated first.

When a program is activated, its variables are allocated in memory and some other one-time initialization code may run. Related programs are activated in activation groups. Activation groups associate the state of related programs.

When a program ends execution and before returning to the caller, the program may be deactivated depending on how the program ended and the characteristics of its activation group.

Program Activation

When a program is called for the first time an instances to the program’s class has to be created. A subsequent call to the program may reuse the program’s instance or it may create a new instance for that call.

Programs and Service Programs are marked with an attribute that specify the activation group where they belong. There are three general possibilities for this attribute. A program may be marked with an activation group attribute to:

  • Be associated with a particular named activation group (ActivationGroup("SomeName")).
  • Have a brand new activation group created and be associated with it (NewActivationGroup).
  • Associate with the activation group of the program that called it (CallerActivationGroup).

Activation Group Creation

Named Activation groups are created when the first program that belongs to it gets activated.

When programs marked with the NewActivationGroup are called, an activation group is created with a system generated name. As described below, the activation group will be deleted when the program returns to its caller.

When a Job starts, it creates an activation group named *DFTACTGRP that is used by default for programs that are not marked with an activation group attribute, typically OPM programs.

Program Deactivation

A program gets deactivated or disposed when its Activation Group is deleted.

When a programs gets deactivated, its Dispose method gets called. The implementation of the Dispose of the program base class calls Dispose on each of the Modules in the program’s module collection.

Deleting an Activation Group

There are three ways for an Activation Group to be deleted:

  • After a program marked with the NewActivationGroup completes its execution and is returning to the calling program.
  • Named activations groups can be deleted by calling the Module method JobServices.ReclaimActivationGroup.
  • When the job reaches its natural end, it deletes all surviving activation groups including *DFTACTGRP.