Why would you use an SRB?

A program uses an SRB to initiate a process in another address space or in the same address space. The advantage of scheduling an SRB is that an SRB routine is asynchronous in nature and runs independently of the scheduling program. This advantage makes SRBs very useful in the following situations, where the scheduling program does not need to wait for the SRB routine to finish running:

• To process in parallel
  In a multi-processor environment, the SRB routine, after being scheduled, can:

  • Be dispatched on another processor and can run concurrently with the scheduling program. The scheduling program can continue to do other processing in parallel with the SRB routine.
  • Run with the same cross-memory environment as the scheduling program and with a DU-AL that is a copy of the scheduling program's DU-AL as it exists when the scheduling program issues the SCHEDULE or IEAMSCHD macro, with the exception of any subspace entries in the scheduling program's DU-AL. The system does not copy subspace entries. In this way, the SRB routine and the scheduling program can access the same address and data spaces.
• To avoid serializing
  Because the SRB represents a separate unit of work, the unit of work that schedules the SRB routine is not serialized or delayed while the SRB routine completes its function. The following types of delays can usually be avoided:

  • Page fault resolution
  • Address space swap-ins
  • Lock suspensions - wait time
• To account for resources
  Because the SRB represents a separate unit of work, the processor time spent accomplishing that work can be charged to:

  • The address space in which the SRB is running
  • The enclave in which the SRB is running
  • The client address space in which the SRB is running
• To make changes of state
  In some instances, a program might be running in some state that prohibits it from performing certain functions. The following are examples of when that program might schedule an SRB routine:

  • A program in a disabled state cannot request a suspend-type lock. The program can avoid these restrictions by scheduling an SRB to complete the function.
  • A program running in cross-memory mode requires functions that only can be performed when in non-cross-memory mode. The program can schedule an SRB that places the SRB routine in non-cross-memory mode.
• To raise the priority of a process

  Because the SRB represents a separate unit of work, the SRB has its own dispatching priority. It can run at a priority higher than that of any address space or at the priority of the address space in which it is scheduled.

  It can also run at a preemptable priority, allowing work at an equal or higher priority to have access to the processor.