HP OpenVMS Systems Documentation

OpenVMS Programming Concepts Manual

June 2002

This manual describes the features that the OpenVMS operating system provides to programmers.

Revision/Update Information: This manual supersedes the OpenVMS Programming Concepts Manual, Version 7.3.

Software Version: OpenVMS Alpha Version, 7.3--1
OpenVMS VAX Version, 7.3

Compaq Computer Corporation
Houston, Texas

Compaq, the Compaq logo, Alpha, OpenVMS, Tru64, VAX, and VMS are trademarks of Compaq Information Technologies Group, L.P. in the U.S. and/or other countries.

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All other product names mentioned herein may be trademarks of their respective companies.

Confidential computer software. Valid license from Compaq required for possession, use, or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor's standard commercial license.

Compaq shall not be liable for technical or editorial errors or omissions contained herein. The information in this document is provided "as is" without warranty of any kind and is subject to change without notice. The warranties for Compaq products are set forth in the express limited warranty statements accompanying such products. Nothing herein should be construed as constituting an additional warranty.

ZK5841

The Compaq OpenVMS documentation set is available on CD-ROM.

This document was prepared using DECdocument, Version V3.3-1e.

Contents

Index

Preface

Intended Audience

This manual is intended for system and application programmers. It presumes that its readers have some familiarity with the Compaq OpenVMS programming environment.

Document Structure

The following chapters provide information about the programming features of the OpenVMS operating system. A list of the chapters and a summary of their content is as follows:

Chapter 1 describes the structure of the two-volume manual, and an introduction to the OpenVMS operating system, and its tools that are available in the programming environment.
Chapter 2 defines the two types of processes, what constitutes the context of a process, and the modes of execution of a process. It also describes kernel threads and the kernel threads process structure.
Chapter 3 describes communication within a process and between processes.
Chapter 4 describes how to use the creation and control of a process or kernel thread for programming tasks. It also describes how to gather information about a process or kernel thread and how to synchronize a program by using time.
Chapter 5 describes overview concepts of symmetric multiprocessing (SMP) systems.
Chapter 6 describes synchronization concepts and differences between the VAX system and Alpha system synchronization techniques. It presents methods of synchronization such as event flags, asynchronous system traps (ASTs), parallel processing RTLs, and process priorities, and the affects of kernel threads upon synchronization. It also describes using synchronous and asynchronous system services, and how to write applications in a multiprocessing It also describes using synchronous and asynchronous system services, and how to write applications in a multiprocessing environment.
Chapter 7 describes the use of the lock manager system services to synchronize access to shared resources. This chapter presents the concept of resources and locks; it also describes the use of the SYS$ENQ and SYS$DEQ system services to queue and dequeue locks.
Chapter 8 describes how to use asynchronous system traps (ASTs). It describes access modes and service routines for ASTs and how ASTs are declared and delivered. It also describes the effects of kernel threads on AST delivery.
Chapter 9 describes the OpenVMS Condition Handling facility. It describes VAX system and Alpha system exceptions, arithmetic exceptions, and Alpha system unaligned access traps. It describes the condition value field, exception dispatcher, signaling, and the argument list passed to a condition handler. Additionally, types of condition handlers and various types of action performed by them are presented. This chapter also describes how to write and debug a condition handler, and how to use an exit handler.
Chapter 10 describes the 32-bit and 64-bit use of virtual address space.
Chapter 11 describes all the services, routines, tools, and programs that support 64-bit addressing.
Chapter 12 describes system services and RTLs of Alpha systems to manage memory. It describes the page size and layout of virtual address space of Alpha systems. This chapter also describes how to add virtual address space, adjust working sets, control process swapping, and create and manage sections on Alpha systems.
Chapter 13 describes the of system services and RTLs of VAX systems to manage memory. It describes the page size and layout of virtual address space of VAX systems. This chapter also describes how to add virtual address space, adjust working sets, control process swapping, and create and manage sections on VAX systems.
Chapter 14 describes how to use RTLs to allocate and free pages and blocks of memory, and how to use RTLs to create, manage, and debug virtual memory zones.
Chapter 15 describes the importance and techniques of instruction and data alignment.
Chapter 16 describes the VLM memory management features, such as the following:
Memory-resident global sections
Fast I/O and buffer objects for global sections
Shared page tables
Expandable global page table
Reserved memory registry
Chapter 17 describes the format used to document system routine calls and explains where to find and how to interpret information about routine calls.
Chapter 18 describes the concepts and conventions used by common languages to invoke routines and pass data between them.
Chapter 19 describes a set of language-independent routines that establish a common run-time environment for user programs.
Chapter 20 describes the system services available to application and system programs for use at run time.
Chapter 21 describes the libraries that contain C header files for routines.
Chapter 22 describes the different I/O programming capabilities provided by the run-time library.
Chapter 23 describes how to use system services to perform input and output operations.
Chapter 24 describes the run-time library (RTL) routines that allow access to various operating system components.
Chapter 25 describes how cross-reference routines that are contained in a separate, shareable image are capable of creating a cross-reference analysis of symbols.
Chapter 26 describes the techniques available for sharing data and program code amoung programs.
Chapter 27 describes the system time format, and the manipulation of date/time and time conversion. It further describes how to obtain and set the current date and time, how to set and cancel timer requests, and how to schedule and cancel wakeups. The Coordinated Universal Time (UTC) system is also described.
Chapter 28 describes file attributes, strategies to access files, and file protection techniques.
Chapter 29 describes the extended file specifications features.
Chapter 30 describes the use of the DECdtm system services to ensure the integrity and consistency of distributed transactions by implementing a two-phase commit protocol.
Chapter 31 describes how to create user-written system services with privileged shareable images for both VAX systems and Alpha systems.
Chapter 32 describes the system services that establish protection by using identifiers, rights databases, and access control entries. This chapter also describes how to modify a rights list as well as check access protection.
Chapter 33 describes how to write a new authentication and credential management (ACM) client program or update existing programs to be an ACM client program.
Chapter 34 describes how to create and use logical name services, how to use logical and equivalence names, and how to add and delete entries to a logical name table.
Chapter 35 describes how to use the LIB$INITIALIZE routine to initialize an image.
Appendix A describes the C language macros for manipulating 64-bit addresses, for checking the sign extension of the low 32 bits of 64-bit values, and for checking descriptors for the 64-bit format.
Appendix B illustrates writing a program with a 64-bit region created and deleted by system services.
Appendix C demonstrates the memory management VLM features described in Chapter 16.
Appendix D describes the use of generic macros to specify argument lists with appropriate symbols and conventions in the system services interface to MACRO assembles.
Appendix E describes the data types that provide compatibility between procedure calls that support many different high-level languages.
Appendix F describes the Digital Distributed Name Service (DECdns) Clerk by introducing the functions of the DECdns (SYS$DNS) system service and various run-time library routines.
Authentication Glossary contains definition for terms used in Chapter 33, Authentication and Credential Management (ACM) System Service.

Reader's Comments

Compaq welcomes your comments on this manual. Please send comments to either of the following addresses:

Internet	openvmsdoc@compaq.com
Mail	Compaq Computer Corporation OSSG Documentation Group, ZKO3-4/U08 110 Spit Brook Rd. Nashua, NH 03062-2698

How To Order Additional Documentation

Visit the following World Wide Web address for information about how to order additional documentation:

http://www.openvms.compaq.com/

Conventions

The following conventions are used in this manual:

Ctrl/ x	A sequence such as Ctrl/ x indicates that you must hold down the key labeled Ctrl while you press another key or a pointing device button.
PF1 x	A sequence such as PF1 x indicates that you must first press and release the key labeled PF1 and then press and release another key or a pointing device button.
`[Return]`	In examples, a key name enclosed in a box indicates that you press a key on the keyboard. (In text, a key name is not enclosed in a box.) In the HTML version of this document, this convention appears as brackets, rather than a box.
...	A horizontal ellipsis in examples indicates one of the following possibilities: Additional optional arguments in a statement have been omitted. The preceding item or items can be repeated one or more times. Additional parameters, values, or other information can be entered.
. . .	A vertical ellipsis indicates the omission of items from a code example or command format; the items are omitted because they are not important to the topic being discussed.
( )	In command format descriptions, parentheses indicate that you must enclose choices in parentheses if you specify more than one.
[ ]	In command format descriptions, brackets indicate optional choices. You can choose one or more items or no items. Do not type the brackets on the command line. However, you must include the brackets in the syntax for OpenVMS directory specifications and for a substring specification in an assignment statement.
\|	In command format descriptions, vertical bars separate choices within brackets or braces. Within brackets, the choices are optional; within braces, at least one choice is required. Do not type the vertical bars on the command line.
{ }	In command format descriptions, braces indicate required choices; you must choose at least one of the items listed. Do not type the braces on the command line.
bold text	This typeface represents the introduction of a new term. It also represents the name of an argument, an attribute, or a reason.
italic text	Italic text indicates important information, complete titles of manuals, or variables. Variables include information that varies in system output (Internal error number), in command lines (/PRODUCER= name), and in command parameters in text (where dd represents the predefined code for the device type).
UPPERCASE TEXT	Uppercase text indicates a command, the name of a routine, the name of a file, or the abbreviation for a system privilege.
`Monospace text`	Monospace type indicates code examples and interactive screen displays. In the C programming language, monospace type in text identifies the following elements: keywords, the names of independently compiled external functions and files, syntax summaries, and references to variables or identifiers introduced in an example.
-	A hyphen at the end of a command format description, command line, or code line indicates that the command or statement continues on the following line.
numbers	All numbers in text are assumed to be decimal unless otherwise noted. Nondecimal radixes---binary, octal, or hexadecimal---are explicitly indicated.

Chapter 1
Overview of Manuals and Introduction to Development on OpenVMS Systems

This chapter describes the structure of the manual. This chapter also provides an overview of the OpenVMS operating system, its components, and the tools in programming software.

1.1 Overview of the Manual

This manual introduces the resources and features of the OpenVMS operating system that are available to help you develop programs. Table 1-1 describes the parts of each volume.

**Table 1-1 Manual Description**
Volume	Part	Description
Volume I
	Part I	Process and Synchronization. Describes the creation, communication, and control of processes. It also describes symmetric multiprocessing (SMP), and the synchronizing of data access, programming operations, and access to resources.
	Part II	Interrupts and Condition Handling. Describes the use of asynchronous system traps (ASTs), and the use of routines and services for handling conditions.
	Part III	Addressing and Memory Management. Describes 32-bit and 64-bit address space, and the support offered for 64-addressing. It also provides guidelines for 64-bit application programming interfaces (APIs); and OpenVMS Alpha, VAX, and VLM memory management with run-time routines for memory management, and alignment on OpenVMS Alpha and VAX systems.
	Part IV	Appendices: Macros and Examples of 64-Bit Programming. Describes the macros used in 64-bit programming, along with two examples of 64-bit programmming.

Volume II
	Part I	OpenVMS Programming Interfaces: Calling a System Routine. Describes the basic calling format for OpenVMS routines and system services. It also describes the STARLET structures and definitions for C programmers.
	Part II	I/O, System and Programming Routines. Describes the I/O operations, and the system and programming routines used by run-time libraries and system services.
	Part III	Generic Macros for Calling System Services. Describes in appendices the generic macros used for calling system services, OpenVMS data types, and the distributed name services on OpenVMS VAX systems.

1.2 Overview of the OpenVMS Operating System

The OpenVMS operating system is a highly flexible, general-purpose, multiuser system that supports the full range of computing capabilities, providing the high integrity and dependability of commercial-strength systems along with the benefits of open, distributed client/server systems.

OpenVMS operating systems can be integrated with systems from different vendors in open systems computing environments. Compaq has "opened" the traditional VMS system to support software that conforms to international standards for an open environment. These industry-accepted, open standards specify interfaces and services that permit applications and users to move between systems and allow applications on different systems to operate together.

The OpenVMS operating system configuration includes OpenVMS integrated software, services and routines, applications, and networks. The system supports all styles of computing, from timesharing to real-time processing to transaction processing. OpenVMS systems configured with optional software support distributed computing capabilities and can function as servers in multivendor client/server configurations.

The OpenVMS operating system is designed to provide software compatibility across all the processors on which it runs:

OpenVMS VAX software runs on the complete family of VAX processors, which support traditional 32-bit processing.
OpenVMS Alpha software runs on a full series of very high-speed RISC processors that support 64-bit as well as 32-bit processing.

Both VAX and Alpha processors encompass a wide range of computing power: from desktop and deskside workstations, through distributed office systems and data center servers, to extremely high performance enterprisewide servers.

The following sections describe the components of the OpenVMS operating system, give a general overview of the system software, and describe the various styles of computing that OpenVMS software supports. The sections also summarize the basic ways in which OpenVMS software can be configured and connected to other software, and the hardware platforms and processors on which the OpenVMS software runs.

1.3 Components of the OpenVMS Operating System

The OpenVMS operating system is a group of software programs (or images) that control computing operations. The base operating system is made up of core components and an array of services, routines, utilities, and related software. The OpenVMS operating system serves as the foundation from which all optional software products and applications operate. The services and utilities in the base OpenVMS operating system support functions such as system management, data management, and program development. Other integrated software that adds value to the system provides functions such as clustering and volume shadowing.

Optional software products, including application programs developed by OpenVMS programmers and other programmers, run on the core operating system. The OpenVMS system supports a powerful, integrated development environment with a wide selection of software development tools supplied by Compaq and other vendors. Application programs written in multiple languages provide computational, data-processing, and transaction-processing capabilities. Thousands of applications have been developed for OpenVMS systems by Compaq and independent software vendors.

Compatibility Between Software Versions

OpenVMS VAX and OpenVMS Alpha software exhibits compatibility from version to version:

User-mode programs and applications created under earlier versions of OpenVMS VAX or OpenVMS Alpha run under subsequent versions with no change.
Command procedures written under one version of OpenVMS continue to run under newer versions of the software.

OpenVMS software developed on VAX platforms can migrate easily to Alpha platforms (see Section 1.3.1.1):

Most OpenVMS VAX images run under translation on OpenVMS Alpha systems.
Most user-mode OpenVMS VAX sources can be recompiled, relinked, and run on an OpenVMS Alpha system without modification. Code that explicitly relies on the VAX architecture requires modification.