If both task level and global DESERV exits have been defined, there is a prescribed calling sequence. The task level exit is called first. If the task level exit indicates that the DESERV function should be terminated (via a return code 4 from the exit), DESERV returns immediately to its caller. However, the global exit is given control when the task level exit returned with return code 0. The global exit can indicate (via return code 4) that control should pass back immediately to the DESERV caller. In this case before returning to the DESERV caller, the task level exit is given control indicating that the DESERV function is complete. After returning from the task level exit, DESERV returns to the caller.

If the global exit returns with return code 0, the DESERV function executes, making the post-processing exit calls. The post processing exit calls are made first to the global exit and second to the task level processing exit. This sequence (the reverse of the pre-processing exit sequence) is chosen to simulate the return sequence that would have been seen if both SVC screen routine and updated SVC routine were in place. The following diagram illustrates the exit routine call sequence:

  DESERV GET, PUT, RENAME, DELETE or UPDATE is issued
    enter DESERV GET, PUT, RENAME, DELETE, or UPDATE
      call task exit for pre-processing
      if return_code = 0 then
        call global exit for preprocessing
        if return_code = 0 then
          process GET, PUT, RENAME, DELETE, or UPDATE
          GOTO post_process_global
        else if return_code = 4 then
          GOTO post_process_task
      else if return_code = 4 then
        return to DESERV caller
 
    Post_process_global:
      call global exit for post-processing
 
    Post_process_task:
      call task exit for post-processing
      return to DESERV caller