CAIDMS Task Management

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CA-IDMS Task Management

• Presented by Manfred Hoefer
• Computer Associates
• UKIUA ROADSHOW 2004

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Abstract

• This session describes the management of online
  tasks running under the AdvantageTMCA-IDMS/DC
  Transaction Server Option (Advantage CA-IDMS/DC)
  or the AdvantageTM CA-IDMS Database Universal
  Communications Facility (UCF) Option. Topics
  include major task control blocks and processing
  modules, how a task is initiated and how the
  Master Task processes interactive terminals. The
  process of task initialization and termination
  and the difference between system mode and user
  mode processing are discussed.

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Agenda

• Overview of Online Task Management
• Starting Online Tasks
• Life Cycle of an Online Task

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What Is an Online Task

• Identifies the user request for work
• Operating system task vs. DC task
• Wait driven processing
• Interrupt driven processing
• Information about request gathered and placed in
  control blocks
• Program to execute
• Priority of request
• User security levels

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Types of Tasks

• Four types of tasks
• System tasks
• External user requests
• Interactive tasks
• Conversational
• Pseudo-conversational
• Background tasks

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System Tasks

• MASTER
• DBRC
• Line driver tasks
• Service tasks
• Database services
• Dictionary run-unit services
• Deadlock detection
• AdvantageTM CA-IDMS Database Performance Monitor
  Option statistics collection
• Factotum tasks
• Helot tasks

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Task Management

• Identifies each user request as a task
• Keeps track of task status
• Determines which task is allowed to process

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Starting Online Tasks

• Task control overview
• Task control data structures
• Task control processing routines
• Attaching a task
• MASTER task processing
• Background task overview
• Timer-initiated tasks
• Startup and Shutdown autotasks
• Queue Threshold tasks
• Attaching a task from an application
• LTE acquisition task ownership

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Task Control Processing

• Maintains a list of active tasks
• Attaches new tasks to process user requests
• Determines task priority and ensures proper
  security
• Passes control to the application program
• Terminates a task
• Limits task utilization of system resources

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Task Control Data Structures

• Logical Terminal Table LTT
• Logical Terminal Element LTE
• Task Definition Table header TDT
• Task Definition Element TDE
• Task Table Search Index TIX
• Task Control Area header TCA
• Task Control Element TCE

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Task Control Components

• RHDCMSTR
• RHDCDBRC
• RHDCTSKC
• RHDCWAIT
• RHDCTSKI
• IDMSTMGR

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Active Tasks

• MAXIMUM TASKS
• MAXIMUM ERUS
• Number of LINE statements
• Plus two for system tasks MASTER and DBRC
• Plus one for each service driver
• Plus one for Print task
• Active task chain anchored at CSADCEFA

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Attaching a Task

• ATTACH macro
• Acquire a TCE
• Add to dispatch list
• Return control
• ECB can be used to delay initial dispatch

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Processing Interactive Tasks

• Terminal control
• Terminal ownership
• Masters Ready Queue
• Handling all terminals

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Processing a Ready Terminal

• A dead terminal
• A new signon
• LTENXTSK
• LTEAUTSK
• Task code entered on terminal
• Previous task abended
• No task code or line I/O session
• Task code is available
• Task is an INPUT task and no input is available
• Task is a NOINPUT TASK or input is available
• Master processes all ready terminals

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A Typical Interactive Processing Cycle

• First connection to DC
• Line driver posts LTTMSECB
• Master sets LTEALIV and attaches factotum
• Factotum writes ENTER NEXT TASK CODE and issues
  read
• Factotum task terminates MASTER waits on PTERECB
• Terminal operator enters task code
• Master finds TDE and attaches task

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A Typical Interactive Processing Cycle (cont'd)

• Task terminates with DC RETURN NEXT TASK CODE
• LTE is put on MASTERs queue
• Master finds TDE but input isnt available
• Operator hits enter
• Line driver posts PTERECB
• Master starts new task

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Background Task Overview

• Timer-initiated tasks
• Queue Threshold tasks
• Startup and Shutdown autotasks
• Application started tasks

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Timer-Initiated Background Tasks

• Interval Control Element - ICE (ICEDS)
• Three types of timer functions
• WAIT
• POST
• START
• TICKER functions

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Queue Threshold Tasks

• Queue name
• TDE of task to start
• Number of records currently in the queue
• Threshold count
• RHDCQUEM attaches task
• IDMSTMGR calls RHDCQUEM to post the ECB when
  queue update is committed

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Autotasks

• Defined in Sysgen
• Startup autotasks attached by Master after Print
  task
• Can preempt any other user tasks
• Master attaches shutdown autotasks after other
  tasks are done
• Master attaches LTE autotasks instead of writing
  ENTER NEXT TASK CODE

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Attaching a Task from an Application Program

• ATTACH from assembler program
• ATTACH from COBOL or PL/I
• Processed like attach by system program
• ECB parm can delay initial dispatch

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Life Cycle of an Online Task

• Attaching a task
• Task initialization
• Task termination
• Making system requests from an application
• Entering and re-entering user mode
• Limiting a tasks resource utilization

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Attaching a Task

• Task creation done by RHDCTSKC
• Locates the first available TCE/DCE pair
• Initializes the DCE and TCE
• Assigns task priority
• For ERUS tasks, associates a TDE with the task
• Allocates a dynamic LTE for background tasks
• Calculates task priority and assigns task limits

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Attaching a Task (cont'd)

• Places the DCE on chain waiting for initial
  dispatch
• Sets a pointer in the TCE to INITLINK or to
  nucleus entry point
• Returns to the program/module which issued the
  ATTACH

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Initial Dispatch

• RHDCWAIT
• Removes the DCE from the TCANEWT chain
• Places the DCE on the active task chain
• Initializes Register 9 to point to the new TCE
• Initializes Register 13 to point to the beginning
  of the stack
• Calls RHDCTSKI to initiate the task

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Task Initialization

• RHDCTSKI
• Moves long-term resources from LTE to TCE
• Moves task limit information from TDERLB to
  TCERLB
• Sets up task initialization statistics
• Calls PERFMON to record tasks initialization
• Calls Exit 4
• Calls the tasks entry point

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Invoking the Initial Program

• The INITLINK routine
• Allocates an LTE for some background tasks
• For ERUS tasks, links to IDMSTASK
• For online tasks, uses TCE-gtTDE-gtPDE
• Issues LINK to application program

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Program Control (RHDCPCTL)

• Entered at PCTLLINK
• Sets indicators in the TCE
• Calls RHDCLODR to locate or load program
• Calls RHDCPCBO to perform setup for COBOL
• Calls RHDCPPLO to perform setup for PL/I
• Calls RHDCLE37 to perform setup for LE
• Sets register values in TCERSA
• Branches to entry point WAITEPI in RHDCWAIT

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Transition to User Mode

• WAITEP2I
• Sets up TCEPMASK
• Sets R8 to point to CSAUMOD1 within RHDCCSA
• Branches to GOTOUSER

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Entering and Reentering User Mode

• GOTOUSER
• Page list for storage protected memory
• Computes time in system mode
• Turns on SVC screening if needed
• Copies the user mode registers from TCERSA to the
  SCA
• Sets TCEUSER and SCAUSER
• Invokes Advantage CA-IDMS SVC if protect in
  effect
• Branches to CSAUMOD1 or CSAUMOD2

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Making System Requests

• Application program controls registers and CPU
• Entry via CSA for system request
• CSA routine branches to WAITEP2
• Set the PSW program mask
• Saves the applications programs AMODE
• Copies user mode registers
• Updates R14 in the RSA

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WAITEP2 processing

• Set the PSW program mask
• Save the application programs AMODE
• Save user mode registers
• Calculates CPU time in user mode
• Turns off SCAUSR
• Calls WAITEP5 (security check)
• Writes a trace entry to log if USER TRACE
• Calls RHDCLIMT
• Calls appropriate processing routine
• Returns to user mode via GOTOUSER

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Terminating a Task

• DC RETURN or RETURN
• PCTLRTN routine
• Processes any parameters specified on the return
  to
• Set LTENXTSK
• Set LTESRPGM
• Set LTERSINT
• Set LTENTPC
• Release the application program (DELETE)
• Pass control to entry point TSKIEP2 within
  RHDCTSKI
• System task does a RTN

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Task Termination Processing

• TSKIEP2
• Call RHDCFLTR for dynamic LTE
• Call IDMSTMGR to perform task end events
• Set up task statistics
• Call Exit 5
• Call PERFMON to record task end event
• Get ERUS statistics
• Write statistics to the log

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Task Termination Processing (cont'd)

• Call Exit 6
• Move long term resources from TCE anchors to LTE
  anchors
• Set LTEMSTR
• Put LTE on Masters ready queue
• If suspended ERUS LTE, post ESEECB to wake up
  DBRC
• If dynamic LTE without LTENXTSK, free the LTE
• Pass control to WAITEP1R in RHDCWAIT

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Detaching a Task

• WAITEP1R
• Remove DCE from the active task chain
• Place TCE/DCE pair on the free task chain
• Post TCAECB
• Branch to DISPATCH to find another task to
  dispatch

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Session Summary

• A Few Words to Review
• DC/UCF functions like an operating system
• Master task manages interactive terminals
• Non-interactive tasks can be created
• Application has control of system while in user
  mode (subject to security restrictions)