What is multithreading in JCL?

Job Control Language does not support multithreading inherently. A method of accomplishment is implemented, known as redneck way, which forks other jobs into INTRDR. This is not risk free. There is an assumption that all the jobs would be finished prior to the next program that pulls in all data processed by other threads.

Another way of accomplishing multithreading is by using system enqueue and duplicate the job names. Use a scheduler that is able to schedule many jobs at once and leaves the next job when all the prereq’s have finished.