When you submit a job (by clicking Submit on the JCL Control page of ESMAC, for example), a new process, called the parent process, is created in which job preparation and all resource allocation for all job steps of the job occurs. Then, if the job preparation and resource allocation is successful, for each program execution,MSS creates a child process in which the program runs. When the program finishes, the child process ends and the parent process wakes up to perform resource deallocation including such actions as disposition processing.
As far as the user exit is concerned, it has knowledge of the following:
A user exit in the child process has no knowledge of events in the parent process, and vice versa.