In the processing phase, JES2 responds to requests for jobs from the z/OS® initiators. JES2 selects from a job queue, jobs that are waiting to run and sends them to z/OS.

By recognizing the current processing phase of all jobs on the job queue, JES2 can manage the flow of jobs through the system.

JES2 Job Scheduling: To process the jobs on the job queue, JES2 communicates with an initiator. An initiator is a system program that starts a job to allow it to compete for system resources with other jobs that are already running.

Initiators are controlled by JES2 or by z/OS workload management (WLM).

• JES2 initiators are started by the operator or by JES2 automatically when the system initializes. The initiators select jobs based on the job class(es) that are assigned to the initiator and the priority of the queued jobs. The system associates each initiator with one or more job classes in a way to encourage the efficient use of available system resources.
• WLM initiators are started by the system automatically based on the performance goals, relative importance of the batch workload, and the capacity of the system to do more work. The initiators select jobs based on their service class and the order in which they were made available for execution.

After JES2 selects a job and passes it to the initiator, the initiator invokes the interpreter to build control blocks from the converter/interpreter text that the converter created for the job.

The initiator then allocates the resources specified in the JCL for the first step of the job. This allocation ensures that the devices are available before the job step starts running. The initiator then starts the program requested in the JCL EXEC statement.

Priority Aging: When all initiators are busy, throughput of certain jobs might fall below normal expectations. To help in these situations, JES2 uses the additional scheduling function of priority aging. Priority aging can help ensure that jobs that have been waiting to run have a chance of being selected to run before those jobs that just entered the system. By using priority aging, a system can increase the priority of a waiting job. The longer the job waits, the higher its priority becomes, up to a limit, and the greater its chances of being selected to run.

JES2-Base Control Program Interaction: JES2 and the base control program communicate constantly to control system processing. The communication mechanism, known as the subsystem interface, allows z/OS to request services of JES2. For example, a requester can ask JES2 to find a job, do message or command processing, or open (access) a SYSIN or SYSOUT data set. Further, the base control program notifies JES2 of events such as messages, operator commands, the end of a job, or the end of a task.