RSCS Task Structure
As described in the previous section, the RSCS,supervisor comprises a
set of routines that function together to manage RSCS system processing.
The supervisor provides a base for many system programs called tasks.
(These tasks are not to be confused with user-application programs.)
The RSCS system service tasks perform less generalized functions fer
the system than those functions performed by the supervisor. Fer
example, the AIS system service task is designed specifically to access
the VM/370 spool file system.
The supervisor identically manages all tasks in RSCS; the superviser makeS no distinction between system service tasks and line driver tasks.
Figure 4 is a list of the Rses tasks and a trief statement of the
service each Ferforms. r
Handles console I/O; accepts requests for services
passed by other system service tasks line
driver tasks; terminates a task; handled program
check interruptions.
Creates a system service or line driver task.
Monitors processing of commands in RSCS; executes
Builds a message element and passes the element
to the appropriate tasks for transmission or
printing. Performs cosmon task functions.
communicates with the spool file system. Manages telecommunications line allocation.
Manages a telecommunications line for a
programmable reaote station using RTAM. Manages a telecommunications line for a remote station terminal. L- __________ __________________________________________________________ _
Figure 4. RSeS Tasks
CREATE SYSTEM TASKS: DMTCRE The main system service task, REX, is loaded with the supervisor during RSCS initialization. The REX task, in turn, creates other tasks
required by the system. DMTCRE reads these other tasks fro. a CMS disk ty. means of a CMS read access method. The task is then started as a new active task under RSCS. Introduction 3-11
PROCESS COMMANDS: DMTCMX DMTCMX receives commands by means of either GIVE request elements passed
ty line driver tasks or in the form.of a console input line resulting
from a console read by DMTREX. The commands DEFINEr COERY, and START (for inactive
links) are executed by DMTCMX. Execution of these commands generally
involves referencing and modification of system status tables (SVECTCRS, TTAGQ, TLINKS, etc.).
If the command is not one that DMTCMX executes within its own cede,
the command line is examined for syntax errors and then passed to the
appropriate task for execution. To do this, DMTCMX generates a
formatted table called a command element to be passed to another active
task for execution via an ALERT asynchronous exit.
The commands CHANGE, ORDER, and PURGE are executed by DMTAXS; the
commands BACKSPAC, CMD, DRAIN, FLUSH, FREE, FWDSPACE, HOLD, MSG, TRACE and START (for active links) are executed by the line driver task fer
the specified link. PROCESS MESSAGES: DMTMGX DMTMGX manages distribution of all RSCS messages, which may be generated by REX or by any other RSCS task. Each message to te issued is
presented to DMTMGX (via GIVE/TAKE for tasks other than REX) along with
an internal routing code and an internal severity code.
Messages may be addressed to the local RSCS operator console, to the local VM/370 operator, to a local VM/310 user console, to a remote
station oFerator, or to any combination of these destinations, by means
of the routing code. The severity code is defined for each message, and
is an indication of the importance of the message. Messages for the RSCS local operator console are enqueued for output
on the RSCS virtual machine console. Messages for the local VM/370 system operator and for local virtual machine consoles are issued by means of execution of a VM/310 MESSAGE command (through the DI1GNCSE interface). Messages for remote RSCS operators are presented to the
line drivers for the associated links by means of the RSCS MSG command
element interface. This method of message handling simplifies RSCS message routing, tracing, and recording.
TERMINATE SYS7EM TASKS AND HANDLE PROGRAM CHECKS: DMTREX When a line driver task requests termination, a TAKE request is passed
to DMTREX specifying that function. DMTREX marks the task as
terminated, then searches for active I/O associated with the taskw If
active I/O is found, it is terminated. To ensure that system integrity
is maintained during the termination of the I/O, a mechanism (at label QUIESB) is set up to handle situations in which an HIO (Halt T/C
instruction) does not take effect immediately.
All RSCS program checks are handled by a routine in DMTREX. program
check diagnostic information is dumped, a message to the operator is
issued, and the RSCS system status is modified, depending on the nature
of the program check.
3-12 IBM VMj370: System Logic and Problem Determination--Volume 3
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