Preventing Service Definition Overlays

Suppose a service administrator extracts a service definition from the WLM couple data set, makes some changes, and in the meantime someone else has extracted, changed, and reinstalled the service definition. If the first user installs the service definition, any changes the second user made will be overwritten. To prevent the service administrator from overwriting the service definition, a program can use:

• The COND parameter on IWMDINST
• The ENQ macro

Using the COND Parameter on IWMDINST

The optional COND parameter lets a caller specify whether or not to install the service definition if the service definition has not been changed since it was extracted from the WLM couple data set. IWMDINST determines whether the service definition has changed by checking a service definition identifier.

The service definition identifier consists of the service definition name, and the time and date the service definition was installed.

Use COND=YES to install the service definition only if the identifier of the currently installed service definition matches the base identifier passed on IN_BASEID parameter. If the identifiers do not match, your program can issue a message stating that the service definition has changed since the last extract. The message can also ask the service administrator to confirm the installation.

Use COND=NO to specify that the input service definition should be installed unconditionally.

When the service definition has been successfully installed on the WLM couple data set, the system issues ENF signal 41. A program can use the ENF macro to know when a service definition has been installed. For more information about how to use ENF signals, see z/OS MVS Programming: Authorized Assembler Services Reference EDT-IXG.

Using the ENQ Macro

To ensure that two service definitions are not installed simultaneously on the WLM couple data set, a program can use the ENQ macro. Programs can serialize installation of the service definition onto the WLM couple data set by obtaining an exclusive ENQ on:

QNAME

SYSZWLM

RNAME

WLM_SERVICE_DEFINITION_INSTALL

SCOPE

SYSTEMS

For more information about how to use the ENQ macro, see z/OS MVS Programming: Authorized Assembler Services Reference EDT-IXG.