During JES initialization, the JES XCF attach/detach exit receives control under the JES main task. At this time, the JES member (JES2 MAS member or JES3 complex member) is attached automatically to the JES XCF group. Each member has a different name, but each is attached to the same group to form the JES XCF group, thereby allowing each to communicate (send messages, obtain member and JES XCF group status, and so on).

IBM recommends that if you attach your own JES XCF group, you do that attach using the JES XCF attach macro, IXZXIXAT, within the attach/detach exit, IXZXIT03. In so doing, you must be careful to not inadvertently cause JES XCF to enter into a recursive set of calls caused by the attach service calling the attach exit. IXZXIT03 - Attach/Detach Exit offers a more complete description of JES XCF processing and Figure 1 provides some sample exit IXZXIT03 code to circumvent potential problems when issuing IXZXIXAT to either acquire a data area or attach an installation-defined group.

Refer to Figure 1 for a graphic view of how IXZXIXAT processing relates to overall JES processing.

Figure 1. JES initialization processing and its relationship to the JES XCF processing

Notice that:

1. JES issues the attach macro, IXZXIXAT, during initialization processing
2. Invocation of the IXZXIXAT macro causes IXZXIT03 to be invoked to get the needed storage for IXZXIT01 and IXZXIT02 processing
3. If coded in exit IXZXIT03, the IXZXIXAT macro attaches your installation-defined group
4. If coded, exit IXZXIT03 gets the storage needed for use of exits IXZXIT01 and IXZXIT02 by members of the installation-defined group.
5. JES initialization continues.

If you require multiple attachments to the JES XCF group, or you determine the need to create an independent, installation-defined JES XCF group, you should add that code to exit IXZXIT03 prior to JES initialization so that those attachments or groups are built during initialization.

If you provide code in IXZXIT03 for attach processing, it may include macro IXZXIXAT. You cannot use any other of the JES common coupling service macros in this exit except IXZXIXDT (if you use IXZXIT03 for detach processing). (Mapping macro IXZ$XPL contains a field that indicates if IXZXIT03 is called for attach or detach processing.)