Task Level Exit

The task level DESERV exit can be established for any TCB following the LPA's initialization. Once established for a task, the DESERV exit is given control for the DESERV functions that are issued under the TCB. The exit entry point is given control twice for each GET, PUT, RENAME, DELETE, or UPDATE invocation; once before DESERV executes and once immediately before the return from the DESERV function. The parameters passed to the exit indicate whether this call happens before or after the DESERV function executes.

If a DESERV FUNC=GET call is made for which there are no PDSEs in the concatenation, the DESERV code issues BLDL to search for the requested names. The task level exit is called in this case. However, if SVC screening is also active, the exit might perform one of the following tasks:

Not process this DESERV call (that is, lets the SVC screen routine process the BLDL request) or
Process this DESERV call with the pre- and post-processing exits, but also disable the SVC screening for BLDL in the pre-processing exit and enable the BLDL screening in the post-processing exit. A parameter passed to the exit indicates whether a BLDL will be or has been issued.

Just as with the SVC screening facility, the DESERV task level exit function enables the user to indicate that the exit should be propagated to subsequently attached tasks.

The first DESERV call for a task searches the TCB chain for a DESERV task level exit routine with propagate specified. DESERV searches the TCB chain following the originating TCB pointer (TCBOTC). If none exists, the task is marked to indicate that no DESERV task level exit exists. Therefore, for the propagate option to work, the exit routine must be established before issuing the ATTACH macro. This is roughly consistent with implementing SVC screening. The difference is that the SVC screening table is propagated at the time of the ATTACH, while the DESERV exit might not be propagated at ATTACH (for example, if the attached program is found in the job pack queue, no directory search (that is, DESERV GET) is done to find the module).