This document describes the purpose of the 3GL CALLNAT interface and its prerequisites and restrictions.
The section covers the following topics:
With the 3GL CALLNAT interface, Natural enables 3GL programs to invoke and execute Natural subprograms.
The 3GL can be any programming language which supports the standard linkage call interface. In most cases this will be a COBOL program, but the functionality can also be used by, for example, PL/1, FORTRAN, C or Assembler programs.
The interface is available in batch mode under the following operating systems:
and for the following TP-monitor environments:
This section describes the prerequisites to execute a Natural subprogram
from a 3GL program, using an internal
CALLNAT statement. To achieve
the desired functionality, a Natural environment must be set up before you
CALLNAT interface from your 3GL program.
The mechanism of parameter addressing in a Natural program requires
that the parameters passed reside in an area allocated by Natural, that is, in
any of its sizes. The 3GL program, however, allocates the storage for its
variables somewhere in the address space of the task. To make addressing still
successful, a "call-by-value" mechanism is used for those
variables which do not already reside in a Natural area. This means that, prior
to invoking the Natural subprogram, the parameters to be passed are transferred
into a Natural area, namely the
In addition to the storage used for the contents of the variables,
additional storage will be needed depending on the number of parameters. The
total amount of space required is approximately the same as the space that
would be needed in the
DATSIZE buffer if the subprogram-invoking
program were coded in Natural.
To invoke the Natural subprogram, the 3GL program must call the
CALLNAT interface. Depending on the power and functionality of the
call interface of the 3GL programming language, the
interface can be either placed in an accessible load library for dynamic
loading or linked to the 3GL program.
It is recommended, whenever possible, to load the
interface dynamically from a Natural steplib, as this method makes sure that
always the most recent version of that program is used.
XNATGCP2 are provided
to elucidate the technique of dynamically loading and calling the
CALLNAT interface from COBOL or PL/I, respectively.
Check with the responsible system programmer for the best solution in your environment.
The foreign 3GL module can be either linked to Natural as a
CSTATIC module and then invoked via a branch and link instruction,
or loaded dynamically and invoked via a TP-dependent link method.
In the latter case, the 3GL module is written in a TP-specific way and
CALLNAT interface must be adapted accordingly. For this
purpose, multiple TP-specific interface modules are provided:
||To be used in the following cases:
||To be used in a CICS environment if the 3GL module has been
||To be used in a CICS environment to build the parameter address
list used as
The invoked Natural subprogram should be terminated with a return to the calling program.
The following statements must not be used.
When used in the invoked Natural subprogram they will bring about an appropriate Natural runtime error (NAT0967).
The parameter values passed by the 3GL program must not reside in a write-protected storage area.
Arrays with dynamic ranges are not possible.
Since BS2000 CRTE does not allow recursions, Natural subprograms, called by the 3GL module, cannot execute any subsequent 3GL calls. A subsequent 3GL call would cause either an enforced abnormal termination of the current Natural session or Natural error NAT0920.
This applies to BS2000 batch, TIAM, and openUTM.
For CICS environments, the 3GL program that uses the Natural 3GL CALLNAT interface must be written for conversational mode. The 3GL program runs on the second CICS program level and pseudo-conversational program technique can therefore not be used.
Under IMS TM and openUTM
IMS TM and openUTM environments running Natural can use the 3GL CALLNAT interface only if both the 3GL program and the Natural subprogram do not issue any terminal I/O; when
WRITE are used in
the invoked Natural subprogram they will bring about an appropriate Natural
runtime error (NAT0967).