This document describes asynchronous Natural processing, a method which is available under all TP monitors supported by Natural.
An asynchronous Natural session is a session which is not associated with any terminal and therefore cannot interact with a terminal user. It can be used to execute a time-consuming task "in the background" without the user having to wait for the task to finish.
This section covers the following topics:
Related Topics:
To identify a session as being asynchronous, the Natural system variable *DEVICE is
assigned the value ASYNCH.
Note
The value of *DEVICE may be modified by the Natural
profile parameter TTYPE and by any SET CONTROL
'T=xxxx' statement; see also profile parameter
TTYPE in the
Parameter Reference documentation and terminal command %T= in the
Terminal Command documentation.
As an asynchronous session is a session that is not associated with any terminal, this
means that any output produced by the session cannot simply be displayed on the screen;
instead, you have to explicitly specify an output destination. You specify this
destination with the Natural profile parameter SENDER when invoking Natural. The
SENDER destination applies to hardcopy output and primary
reports; any additional reports are sent to the destinations specified with the DEFINE PRINTER statement, just as in
a synchronous online session.
As an asynchronous session can also cause a Natural error, the destination to which any
Natural error message is to be sent must also be specified; this is done with the Natural
profile parameter OUTDEST. This parameter also provides an option to
have error messages sent to the operator console. After an error message has been sent,
Natural terminates the asynchronous session.
The profile parameters SENDER and OUTDEST
should be set accordingly to be prepared for unexpected output by the asynchronous Natural
session; otherwise, the asynchronous Natural session may abend in such a scenario.
An asynchronous Natural session only has the Natural stack to enter the name of Natural
programs and Natural system commands to be executed. If a Natural program or a Natural
system command fails with an unhandled Natural error or if the entire Natural stack is
exhausted and NEXT mode would be entered, the asynchronous Natural session is
terminated with termination message NAT9943.
Depending on the TP monitor in use and depending on the TTYPE setting, either the
CLEAR key or the EOF indicator is passed back to Natural on an
INPUT request by default. This measure helps to prevent error loop
situations if a program unintentionally executes an INPUT statement. To pass
the ENTER key indicator back, you can issue a SET CONTROL 'N'
statement prior to the INPUT statement.
Tip
You can make your application compatible with asynchronous sessions by evaluating the
system variable *SCREEN-IO accordingly.
The following Natural profile parameters should be considered in the case of an asynchronous Natural session:
| Profile Parameter | Comment |
AUTO
|
Asynchronous sessions may have non-alphabetical user IDs. In this case,
AUTO=ON will fail.
|
CM
|
An unwanted input situation may happen if the Natural session accidentally
falls onto the NEXT level. Setting CM=OFF will terminate
the session immediately in such a situation.
|
ENDMSG
|
The error message NAT9995 (normal termination message) can be suppressed by
specifying ENDMSG=OFF.
|
IMSG
|
Natural initialization error messages and warnings can be suppressed by
specifying IMSG=OFF.
|
MENU
|
Asynchronous sessions only have the Natural stack for command
inputs; therefore, it is recommended to specify MENU=OFF and to
navigate through Natural by using direct commands.
|
PLOG |
Dynamic parameter logging is executed by sending all
parameters line by line to the SENDER destination.
|
PROGRAM
|
If a standard back-end program/transaction is defined in your installation,
it should be checked if this program can run asynchronously or if it is desired to
deal with terminal-bound sessions only. Specifying PROGRAM=0 bypasses
the back-end logic.
|
