gtpd1m2uDatabase Reference

Coupling Facility Support

Coupling facility (CF) support provides data sharing capabilities that allow subsystems, system products, and applications running in a processor configuration to use a CF for high-performance, high-availability data sharing. The CF is a processor that attaches to other processors in a loosely coupled configuration to perform special-purpose operations. CF support provides connectivity to a CF for use by TPF system functions. CF support allows as many as 32 CFs and provides two types of CF structures that are used to perform various operations:

You can add one or more CFs from a TPF processor to the processor configuration. Applications can connect to CF list or cache structures on CFs that have been added to the processor configuration and use connection services to manage data in that CF structure. See Connection Services for more information. The first TPF system to connect to a CF structure allocates the structure in a CF and defines the structure attributes. When a TPF system no longer requires access to the CF structure, the TPF system can disconnect from that structure. See Connecting to a Coupling Facility Structure and Disconnecting from a Coupling Facility Structure for more information about connecting to and disconnecting from CF structures.

Other TPF systems can connect to the existing CF structure (either list or cache) by name, but cannot change the structure attributes of that CF structure as long as it remains allocated. See Defining Structure Attributes for Coupling Facility Structures for more information about defining structure attributes.

An application that connects to a CF list structure can monitor individual lists to determine when list entries have been created on the list. When a list changes from empty state to nonempty state (that is, when a list entry is added to a previously empty list), an application-defined exit is called. This eliminates the need for application polling of lists and simplifies programming requirements.

An application that connects to a CF cache structure can automatically notify affected TPF systems when shared data in the cache is changed. The application can also determine whether the local copy of shared data is valid by checking system-maintained validity indicators.