Creating memory objects

To create a memory object, use the IARV64 GETSTOR service. When you create a memory object, request a size large enough to meet long-term needs; the system, however, abends a program that unconditionally tries to obtain more storage above the bar than the MEMLIMIT allows. IBM® recommends that you specify COND=YES on the request to avoid the abend. In this case, if the request exceeds the MEMLIMIT, the system rejects the request but the program continues to run. The IARV64 service returns to the caller with a non-zero return code. The recovery routine would be similar to one that would respond to unsuccessful STORAGE macro conditional requests for storage.

The SEGMENTS parameter specifies the size, in megabytes, of the memory object you are creating. The system returns the address of the memory object in the ORIGIN parameter.

Other parameters further define the memory object:

FPROT=YES gives it fetch protection.
TTOKEN=ttoken indicates what task is to own the memory object.
USERTKN=usertoken is an 8-byte token that relates two or more memory objects to each other. Later, the program can request a list of memory objects that have that same token and can delete them as a group.

When a program creates a memory object, it can specify, through the GUARDSIZE and GUARDHIGH and GUARDLOW parameters, that the memory object is to consist of two different areas. One area is called a guard area; this storage is not accessible; the other area is called the usable area. A later request can change the guard area into a usable area. Creating a guard area and changing its size can help you understand the important purposes for this kind of memory object.

Before issuing IARV64, issue SYSSTATE ARCHLVL=2 so that the macro generates the correct parameter addresses.