Multiple Request Parameter Lists or Data Sets

If the exit routine is used by a program that is doing asynchronous processing with multiple request parameter lists (RPL) or if the exit routine is used by more than one data set, you must code the exit routine so that it can handle an entry made before the previous entry's processing is completed. Saving and restoring registers in the exit routine, or by other routines called by the exit routine, is best accomplished by coding the exit routine reentrant. Another way of doing this is to develop a technique for associating a unique save area with each RPL.

If the LERAD, EODAD, or SYNAD exit routine reuses the RPL passed to it, you should be aware of these factors:

The exit routine is called again if the request issuing the reused RPL results in the same exception condition that caused the exit routine to be entered originally.
The original feedback code is replaced with the feedback code that indicates the status of the latest request issued against the RPL. If the exit routine returns to VSAM, VSAM (when it returns to the user's program) sets register 15 to also indicate the status of the latest request.
JRNAD, UPAD, and exception exits are extensions of VSAM and, therefore, must return to VSAM in the same processing mode in which they were entered (that is, cross-memory, SRB, or task mode).