The workflow engine loads the instance data for the list workflow data object associated with the parallel activity. For each item in the list workflow data object, a new instance of the wrapped activity is created and executed. The details of what occurs when these instances of the wrapped activity are executed may be found in the relevant chapters describing the activities that a parallel activity can wrap (Manual and Decision).
At runtime, the Workflow Engine treats a Parallel Activity as if it were multiple activities, contained within a Parallel (AND) Split/Join block. One Activity Instance is created per item in the Parallel Activity List WDO (e.g. if that list contains three items, then three Activity Instances will be created). This ensures that all of the activity instances associated with the parallel activity must be completed before the actual parallel activity is deemed to be complete and the workflow can progress.
In order to resolve the mappings associated with a Parallel Activity, each instance of the wrapped activity is associated with one item from the Parallel Activity List WDO. The item is indexed using the Context_Parallel Workflow Data Object (e.g. ChildDetailsListWDO[Context_Parallel.occurrenceCount]).