An active Natural session uses CICS resources such as thread storage, roll facility entries (that is, records in a VSAM RRDS file, in a CICS temporary storage queue or main memory) as well as Roll Server slots. These resources are allocated by Natural CICS Interface and correctly released whenever a session under control of Natural CICS Interface terminates normally or abnormally.
If a Natural session termination is not controlled by Natural CICS Interface, a node error program helps to correctly release the acquired resources.
This document discusses CICS node error program and timeout considerations.
The following topics are covered:
See also:
For information on installing a CICS node error program, refer to the corresponding section in Installing Natural CICS Interface on z/OS in the Natural Installation documentation.
In the following situations, Natural CICS Interface does not receive control at session termination and, therefore, cannot properly release the resources still held by the session:
A non-Natural program called by Natural issues an EXEC CICS ABEND
CANCEL command to terminate the CICS task abnormally.
Some CICS monitor products offer tools to purge CICS tasks, thus bypassing any abnormal termination exit set by the application.
A user disconnects a terminal from the CICS region (by switching the power off or using an adequate session manager function) while the respective Natural session is not active in CICS (pseudo-conversational screen I/O) at that time.
A user has been inactive in the Natural terminal session for the period specified
with the TIMEOUT parameter in the CICS segment of the RACF user
profile.
Natural CICS Interface provides some recovery mechanisms to recover from such situations.
For example:
Whenever a new Natural session is to be started, Natural checks whether another session with the same terminal ID is active. If such a session exists, it is logically terminated, and all its resources are released prior to starting the new session.
However, if COMARET=OFF is set in the NTCICSP macro,
the information to resume a Natural session is kept in a CICS temporary storage record
where the terminal ID is part of the storage queue name. As a result, another CICS user
who tries to start a Natural session with this terminal ID will resume the old session
rather than starting a new session. Therefore, we strongly recommend that you set
COMARET=ON.
CICS provides the node error program (NEP) exit interface DFHZNEP, which is
called when a user disconnects a terminal from the CICS region. The session is lost if the
user disconnects the terminal while the respective Natural session is not active in CICS.
You can then use DFHZNEP to execute the Natural-specific NCIZNEP node error program and
terminate the lost session. This program is delivered with Natural CICS Interface (see
also Natural CICS Sample
Programs).
If an active and running Natural session is canceled
using CEMT SET TASK(...) FORCEPURGE
using CEKL SET TASK(...) FORCEPURGE
by a CICS monitoring product
by flushing the Natural session using SYSTP
the respective CICS task is terminated immediately with CICS abend AKEH without NCIZNEP being executed for session cleanup.
CICS provides the DFHZNEP default node error program (NEP) that is called when a user disconnects a terminal from the CICS region. Furthermore, CICS provides the DFHZNEPX sample program that is designed for customized error handling in order to invoke user-supplied error processors.
Natural CICS Interface provides the Natural-specific NCIZNEP node error program. You
can use the XNCINEP2 sample node error program in order to set up DFHZNEP and
execute NCIZNEP to terminate a lost session. XNCINEP2 can be
used instead of the sample program DFHZNEPX.
XNCINEP2 performs the following functions:
Enables an error processor to receive control for all possible error codes passed to
DFHZNEP. If XNCINEP2 receives control, it issues a CICS trace request
that shows with which error codes DFHZNEP has been invoked on certain actions and
related TCTTE error information.
Calls the NCIZNEP module via EXEC CICS LINK which performs
a Natural session cleanup.
The XNCINEP2 sample program is supplied in the source library of Natural
CICS Interface. If DFHZNEPX has already been customized, copy the relevant source code
from XNCINEP2 into DFHZNEPX and insert it into an appropriate position before
the trailing EXEC CICS RETURN call in DFHZNEPX, considering other products or
components for which error processing is performed.
NCIZNEP tries to resume a session asynchronously and subsequently terminate
it logically based on the session restart information
(NEXTTRANSID and restart data in COMMAREA or CICS temporary
storage) of a terminal session with pending pseudo-conversational screen I/O.
Upon completion, NCIZNEP cleans the parameter input indicating to the caller
(usually DFHZNEP) whether it has successfully completed its work and launches
the cleanup task for the Natural session.
If more than one Natural CICS Interface version is active in a CICS system, cleanup
processing performed by the called Natural version-specific node error program can fail,
because the Natural session to be terminated is hosted by a different Natural CICS
Interface version. Upon execution completion of NCIZNEP, DFHZNEP
can test whether the operation was successful. If the operation was not successful,
NCIZNEP will call another node error program related to a different Natural
CICS Interface version.
If a user disconnects a terminal from the CICS region while the respective Natural
session is not active in CICS, DFHZNEP can receive control more than once for
various internal error codes, since each internal error code is related to a specific CICS
error message.
If you want NCIZNEP to attempt to immediately purge a currently active
Natural session for which NCIZNEP receives control, specify
PURGE=YES for the NCIZNEP module. See the installation
procedure for Natural CICS Interface and the section CICS Startup
Parameters in Installing
Natural CICS Interface on z/OS in the Natural
Installation documentation.
In general, the following is required for MRO/CICSPlex environments:
DFHZNEP and NCIZNEP must be installed in the TOR.
The NCIZNEP module must be defined in CICS with
EXECKEY(CICS).
For MRO/CICSPlex environments where you want NCIZNEP to purge a currently
active Natural session, consider the following additional requirements:
The NCIZNEP module must also be defined in the CICS AORs associated
with a TOR. A Natural session can only be purged in the AOR where a transaction is
started to purge the task.
A transaction ID must be defined for the NCIZNEP module in the CICS
TOR and the AORs with the attributes TASKDATAKEY(CICS) and
PRIORITY(255)
The transaction ID must also be specified with the NEPTRAN
parameter in the CICS startup parameters for the NCIZNEP module as
described in Installing Natural CICS Interface on z/OS in the
Natural Installation documentation.
The Natural transactions for which you want to purge currently active Natural
sessions have to be defined in CICS with the attribute SPURGE(YES).
If you want to call the node error programs NCIZNEP (for Natural CICS
Interface) and CORNEP (for Adabas System Coordinator) from DFHZNEP, you should consider that both
NCIZNEP and CORNEP may attempt to release Adabas-related
resources at the same time. In order to avoid interferences due to concurrent execution,
always call NCIZNEP before CORNEP and slightly delay the start
time of CORNEP to make sure that NCIZNEP has completed before
CORNEP starts executing.
For more information, see the Adabas System Coordinator Installation documentation.
If a user session is timed out, the resources held by the Natural session are not
released by CICS. A user session is timed out, for example, if the user has been inactive
in the Natural terminal session for the period specified with the
TIMEOUT parameter in the CICS segment of the RACF user
profile.
In the case of a timeout due to the setting of the TIMEOUT
parameter in the RACF user profile, the action that CICS performs is determined by the
value of the GNTRAN system initialization parameter. Natural
resources are not properly released if either GNTRAN=NO is set or the
executed "good night" program does not call the NCIZNEP
module.
To make sure that all resources held by Natural are properly released
For the GNTRAN parameter, specify a CICS transaction ID for
which the PROGRAM attribute specifies XNCIGNIT.
Use the XNCIGNIT sample node error program supplied in the source
library of Natural CICS Interface (see also Natural CICS Sample Programs) and define it in
CICS.
XNCIGNIT must be assembled and linked with the CICS EXEC
interface modules DFHELII and DFHEAI0.
XNCIGNIT calls the NCIZNEP module via EXEC CICS
LINK, which performs a Natural session cleanup.
You must perform the following for MRO/CICSPlex environments:
In the TOR, define and install the XNCIGNIT sample program and the CICS
transaction ID for which the PROGRAM attribute specifies
XNCIGNIT.
In the XNCIGNIT sample node error program, add the
SYSID parameter to the EXEC CICS LINK statement
that executes NCIZNEP. SYSID must specify the
system name of an AOR that relates to the TOR. You can specify any AOR, because a CICS
task is not active for a session in an AOR when the session is timed out.
The USR4006N application programming interface (API) allows you to retrieve or cancel Natural sessions based on selection criteria, such as the period of inactivity of terminal sessions.
It can happen that all sessions are read sequentially to find one or more sessions that
match a specified criterion because USR4006N is not able to randomly select sessions by a
specific criterion. Therefore, we recommend that you execute USR4006N only occasionally,
and only if you want to remove all Natural sessions that satisfy a specific criterion in a
single run. Alternatively, you can use the NCIZNEP module and the
XNCIGNIT sample node error program which operate on a single Natural
session only and need not access all sessions.