MVS Jan 2005.p65 - CBT Tape

Multi-tasking with IBM C/C++ programs
Inter- and intra-address space multi-tasking is a very powerful
capability providing one of the very basic tools associated with
MVS and all its successor operating systems. Multiple code
paths can be active simultaneously either within the same
address space or in secondary address spaces, allowing for
very complex application support. This capability extends to
programs written in IBM C/C++ and a number of techniques
are inherently available for this purpose.
INHERENT MULTI-TASKING TECHNIQUES
Several techniques are available for employing multi-tasking
functionality in IBM C/C++. Let’s discuss the more common
techniques – fork(), spawn(), pthread_create(), and the C
Multi-Tasking Facility (MTF).
THE FORK() FUNCTION
One of the classic multi-tasking tools in C/C++ is the fork()
function call. The fork() function performs as follows.
The issuer of the fork() function (the parent process) creates
a new unit of work (the child process) that, for all intents and
purposes, is a clone of the parent. Execution in both the parent
and the child process continues from the point immediately
following the fork() function call. To determine whether this is
a parent or a child process, a simple check of the return code
from fork() can be made. If the return code is less than 0, the
fork() function call has failed and the errno variable can be
examined to obtain additional information regarding the failure.
If the return code is greater than 0, program execution is in the
parent process and the return code value from the fork()
function call is the process id (PID) of the created child
process. If the return code is equal to 0, program execution is
in the child process. Programmatically, this could look
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