Subtask sharing is the ability to perform multiple OPENs to the same data set within a task or from different subtasks in a single address space and still share a single control block structure. Subtask sharing allows many logical views of the data set while maintaining a single control block structure. With a single control block structure, you can ensure that you have exclusive control of the buffer when updating a data set.

If you share multiple control block structures within a task or address space, VSAM treats this like cross-address space sharing. You must adhere to the guidelines and restrictions specified in Cross-Region Sharing.