MVS Jan 2005.p65 - CBT Tape

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CVT DSECT=YES,LIST=YES EJECT IHAASVT LIST=YES EJECT IHAASCB LIST=YES EJECT IHAASSB LIST=YES EJECT DCBD DEVD=(DA,TA),DSORG=(QS,BS) END Michel Joly Systems Programmer (France) © Xephon 2005 Why not share your expertise and earn money at the same time? MVS Update is looking for program code, CLISTs, REXX EXECs, JavaScript, etc that experienced users of MVS (OS/390, z/OS) have written to make their life, or the lives of their users, easier. We are also looking for explanatory articles, and hints and tips, from experienced users. We would also like suggestions on how to improve MVS performance. We will publish your article (after vetting by our expert panel) and send you a cheque, as payment, and two copies of the issue containing the article once it has been published. Articles can be of any length and should be e-mailed to the editor, Trevor Eddolls, at trevore@xephon.com. A free copy of our Notes for Contributors, which includes information about payment rates, is available from our Web site at www.xephon.com/nfc. 26 © 2005. Xephon USA telephone (214) 340 5690, fax (214) 341 7081.
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 © 2005. Reproduction prohibited. Please inform Xephon of any infringement. 27
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Page 73: MVS news TPS Systems has announced

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