Using an API to serialize resources

You can choose from the following macros to serialize access to global resources:

The ISGENQ macro provides the most flexibility because it allows you to obtain, change, release, and test resources while supporting the following modes:

AMODE 31 and 64
Primary or AR ASC mode

Guideline: As of z/OS® V1R6, IBM® recommends using the ISGENQ service for unauthorized serialization requests, although the ENQ, DEQ, and RESERVE interfaces will continue to be supported.

The following table shows how to serialize access to resources at three levels:

Table 1. API Serialization in MVS
To serialize access to a resource:	Macro	Scope
Within an address space	ISGENQ, ENQ and DEQ	STEP
Within a single system	ISGENQ, ENQ and DEQ	SYSTEM
Across a sysplex	ISGENQ	SYSTEMS or SYSPLEX
Across a sysplex	ENQ, RESERVE and DEQ	SYSTEMS

Note: To serialize access to resources across sysplexes and between VM and z/OS establish a reserve through the RESERVE macro or ISGENQ macro with the RESERVEVOLUME=YES parameter. Because this serialization involves I/O to the entire volume; you lose much of the granularity of the qname and rname resource abstraction.

As of z/OS V1R6, use the ISGENQ macro to obtain, change, release resources, test an obtain request, and reserve a DASD volume.

For detailed information about using the ISGENQ macro:

For the ISGENQ macro description, see ISGENQ macro.
For the ISGENQ macro defaults, see z/OS MVS Programming: Assembler Services Reference IAR-XCT.

The RESERVE macro obtains access to a resource and the DEQ macro frees the resource. The RESERVE macro, by default, has a scope of SYSTEMS. The corresponding DEQ macro must specify a scope of SYSTEMS.

The ENQ macro with a scope of SYSTEMS obtains access to a resource. The DEQ macro frees the resource when you specify a scope of SYSTEMS.

Guideline: Some applications may require specific RNL changes for ENQs or related products that are installed.

Note:

A scope of SYSTEMS indicates that MVS is to protect the resource across multiple systems.
Using the ENQ macro with a scope of SYSTEMS requires a multisystem approach to resource serialization. Your installation combines the systems that must serialize access to resources in a global resource serialization complex. For more information, see Advantages of using global resource serialization.