Terminating the external subsystem connection

IMS terminates the external subsystem connection (control region connection) in an orderly manner in a number of different circumstances.

IMS terminates the external subsystem connection (control region connection) in an orderly manner when one of the following occurs:
  • IMS processes a /STOP SUBSYS command.
  • The external subsystem (ESAP) activates the IMS subsystem termination service exit routine.
  • The external subsystem posts the termination ECB provided on the Identify exit routine invocation.
  • Certain attach processing errors are encountered.
  • IMS is shutting down.

IMS allows existing threads to the external subsystem to complete processing. When all threads have terminated, IMS terminates the connection by activating the Terminate Identify exit routine from the control region.

When the connection is terminated due to a /STOP SUBSYS command, the termination ECB being posted, or processing errors, IMS puts the external subsystem connection in stopped status. Once in stopped status, IMS does not allow a connection to be reestablished. A /START SUBSYS command is required to remove the stopped status.