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When an abnormal condition occurs
When an abnormal condition associated with a particular terminal or line occurs, the
terminal control program puts the terminal out of service and passes control to the
terminal abnormal condition program (DFHTACP) which, in turn, passes control to a
version of the terminal error program (DFHTEP, either CICS-supplied or
user-written), so that it can take the appropriate action.
Terminal control program
When the terminal from which the error was detected has been put out of service,
the terminal control program creates a terminal abnormal condition line entry
(TACLE), which is chained off the real entry, the terminal control table line entry
(TCTLE) for the line on which the error occurred. The TACLE contains information
about the error.
Terminal abnormal condition program
After the TACLE has been established, a task that executes DFHTACP is attached
by the terminal control program and is provided with a pointer to the real line entry
(TCTLE) on which the error occurred. After performing basic error analysis and
establishing the default actions to be taken, DFHTACP gives control to DFHTEP,
and passes a communication area (DFHTEPCA) so that DFHTEP can examine the
error and provide an alternative course of action.
The communication area provides access to all the error information necessary for
correct evaluation of the error; and contains special action flags that can be
manipulated to alter the default actions previously set by DFHTACP.
After DFHTEP has performed the desired function, it returns control to DFHTACP
by issuing an EXEC CICS RETURN command. DFHTACP then performs the
actions dictated by the action flags within the communication area, and the
error-handling task terminates.
Notes:
1. DFHTACP default actions, message codes, error codes, and conditions are
listed in the
CICS Problem Determination Guide
.
2. If DFHTACP has more than eight errors on a line before action can be taken,
the line is put out of service to avoid system degradation.
Terminal error program
The terminal error program analyzes the cause of the terminal or line error that has
been detected by the terminal control program. The CICS-supplied version (the
sample terminal error program, DFHXTEP) is designed to attempt basic and
generalized recovery actions. A user-written version of this program can be provided
to handle specific application-dependent recovery actions. The user-written terminal
error program is linked-to in the same way as the CICS-supplied version, by the
terminal abnormal condition program. Information relating to the error is carried in
the communication area and the TACLE.
The macros that are provided for generating the sample terminal error program are
described in the sections that follow. The main steps are generating the sample
background
416
CICS TS for OS/390: CICS Customization Guide