During IFG0EX0B-related processing, system enqueues are issued to serialize system functions. These enqueues might prevent other system services from completing successfully. In particular, IFG0EX0B should not start dynamic allocation, open, close, end-of-volume, or DADSM functions, because of an enqueue on the SYSZTIOT resource.

If IFG0EX0B requires access to an installation data set, the control blocks needed to access that data set (DCB, DEB) should be built during system initialization. RACF macros can be called from the exit.

If your exit does not update a particular DCB during a parallel open and that DCB does not have an exit list with a DCB OPEN exit entry or a JFCBE entry, then when your exit is processing a different DCB for the same OPEN, the two copies of the first DCB might differ. OPEN will make them consistent later.