Proper serialization of shared memory objects

It is important to serialize access to shared memory objects so that the shared memory objects your program creates and uses do not cause situations where z/OS® finds reason to abnormally end the work unit. Shared memory objects can be serialized with ENQs, Latches, or other cross-address space serialization techniques.

The following example shows the behavior of memory objects when strict serialization is not maintained.

Example: Tasks A, B, and C are sharing storage through a GETSHARED request obtained by task A. Task B and C are continually sharing the storage via SHAREMEMOBJ and DETACH AFFINITY=LOCAL. They continue sharing until task A chooses to DETACH AFFINITY=SYSTEM to the shared storage while both of the following conditions apply:

Task B still holds an interest in the storage and
Task C no longer has a local interest in the shared storage (issued DETACH AFFINITY=LOCAL).

If work unit C tries to share the memory object again (through SHAREMEMOBJ), the system will issue an abend code DC2 with reason code xx0040xx because it was not serialized against the DETACH AFFINITY=SYSTEM issued by work unit A.