Default Heap

The first request for dynamic storage from the default heap within an activation group that is using single-level storage results in the creation of a default heap from which the storage allocation takes place. If there is insufficient storage in the heap to satisfy any subsequent requests for dynamic storage, the system extends the heap and allocates additional storage.

Allocated dynamic storage remains allocated until explicitly freed or until the system discards the heap. The default heap is discarded only when the owning activation group ends.

Programs in the same activation group automatically share dynamic storage provided the default heap allocated the storage. However, you can isolate the dynamic storage that is used by some programs and procedures within an activation group. You do this by creating one or more heaps.