gtpd1m2yDatabase Reference

Coupling Facility Structure Concepts

Whether a CF structure is defined as a CF list structure or a CF cache structure, certain characteristics are common to both types. The topics that follow provide basic information about both types of CF structures.

Defining Structure Attributes for Coupling Facility Structures

When using the CFCONC macro to connect to a CF structure, specify structure attributes that describe the CF structure you need. Whether the TPF system uses the structure attributes you specify depends not only on your CFCONC parameters, but also on resource availability in the CF and whether you are the first to issue the CFCONC macro for the CF structure, therefore causing its allocation.

The CF structure to which you receive connectivity may or may not meet all your requirements. The TPF system returns the actual structure attributes to you in the CFCONC answer area, which is mapped by the ICFAA data macro. It is your responsibility to verify that the structure attributes, as indicated in the CFCONC answer area, are acceptable. If you decide not to accept one or more of the structure attributes, you can disconnect from the CF structure.

See Specifying Structure Attributes for Coupling Facility Structures for a description of the structure attributes that are required on the CFCONC macro.

Identifying Connection States

A connection to a CF structure can be in one of two states:

Understanding Structure Persistence

The structure attribute of persistence applies to CF list structures and CF cache structures. The persistence attribute of a CF structure is affected by how you define your structure disposition.

The structure disposition (the STRDISP parameter on the CFCONC macro) determines whether the CF structure remains allocated when there are no active connections to either CF structure. A structure disposition of KEEP indicates that when there are no active connections to the CF structure, that structure remains allocated. For example, if data in the CF structure needs to be kept permanently in the CF, specify a structure disposition of KEEP by coding STRDISP=KEEP on the CFCONC macro. A CF structure that remains allocated when there are no active connections is called a persistent structure.

A structure disposition of DELETE (by coding STRDISP=DELETE) indicates that when there are no active connections to the CF structure, that structure is deallocated. However, if there any active connections to the CF structure, that structure remains allocated.

See Specifying Structure Attributes for Coupling Facility Structures for more information about the STRDISP parameter. See TPF System Macros for more information about the CFCONC macro.