Abstract: Two or more user applications executing on one or more processors, each controlled by an operating system, share use of a list and subsidiary list structure within a Structured External Storage (SES) facility to which each processor is connected. One of the applications registers interest in particular state transitions affecting one or more subsidiary lists within the list structure, causing a process within the SES to notify the appropriate processor when a list operation causes the particular state transition, without interrupting processing on the processor. The application receives notice of the state transition by periodically polling a vector within the processor, or by receiving control when a test by the operating system of a summary indicator for the vector causes an application exit to be driven.

Abstract: A method and apparatus for optimizing a data structure of an external data storage facility shared by a plurality of data processing systems, the data structure being allocated by a first allocation command which includes first allocation parameters based on an amount of storage space in the external data storage facility assigned for creation of the data structure and a composition of the data structure, includes a device for determining values of the first allocation parameters, to thereby determine a first composition of the data structure, a device for determining an actual usage of the data structure, to thereby determine a second composition of the data structure, a device for comparing the first composition of the data structure with the second composition of the data structure, and a device for issuing, based on an output from the comparing device, a second allocation command having second allocation parameters, to the data structure for reallocation thereof.