Write about the software architecture concurrency patterns below and explain how they work : ? Rendezvous, Round Robin, Static Priority, and Dynamic Priority. The primary reference is thi

Table of Contents

Real-Time Design Patterns: Robust Scalable Architecture for Real-Time Systems

By Bruce Powel Douglass

Publisher : Addison Wesley

Pub Date : September 27, 2002

ISBN : 0-201-69956-7

Pages : 528

When creating real-time and embedded (RTE) systems, there is no room for error. The nature of the final product demands that systems be powerful, efficient, and highly reliable. The constraints of processor and memory resources add to this challenge. Sophisticated developers rely on design patterns—proven solutions to recurrent design challenges—for building fail-safe RTE systems.

Real-Time Design Patterns is the foremost reference for developers seeking to employ this powerful technique. The text begins with a review of the Unified Modeling Language (UML) notation and semantics then introduces the Rapid Object-Oriented Process for Embedded Systems (ROPES) process and its key technologies. A catalog of design patterns and their applications follows.

Key topics covered in this book include:

• Identifying large-scale strategic decisions that affect most software elements • Coordinating and organizing system components and subsystems • Managing memory and resources • Defining how objects can be distributed across multiple systems • Building safe and reliable architectures • Mapping subsystem and component architectures to underlying hardware

The book's extensive problem-solving templates, which draw on the author's years in the trenches, will help readers find faster, easier, and more effective design solutions.

The accompanying CD-ROM (Examples link) contains:

• Related papers • Object Management Group (OMG) specifications • Rhapsody(TM)—a UML-compliant design automation tool that captures the

analysis and design of systems and generates full behavioral code with intrinsic model-level debug capabilities

• RapidRMA(TM)—a tool that integrates with Rhapsody(TM) to perform schedulability and timeliness analysis of UML models

TE AM FL Y

Team-Fly®

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Table of Content Table of Content …………………………………………………………………………………………………… i Copyright……………………………………………………………………………………………………………… v

Dedication ………………………………………………………………………………………………………. vi Foreword…………………………………………………………………………………………………………….. vi

References ……………………………………………………………………………………………………. viii Preface ……………………………………………………………………………………………………………… viii

Goals …………………………………………………………………………………………………………….. viii Audience……………………………………………………………………………………………………….. viii Organization …………………………………………………………………………………………………… ix More Information …………………………………………………………………………………………….. ix Acknowledgments ……………………………………………………………………………………………. x

Part I: Design Pattern Basics …………………………………………………………………………………… 1 Chapter 1. Introduction ………………………………………………………………………………………… 2

1.1 Basic Modeling Concepts of the UML………………………………………………………… 2 1.2 Models……………………………………………………………………………………………………….. 3 1.3 Structural Elements and Diagrams …………………………………………………………….. 4 1.4 Behavioral Elements and Diagrams …………………………………………………………. 21 1.5 Use Case and Requirements Models ………………………………………………………. 32 1.6 What Is a Design Pattern? ……………………………………………………………………….. 34 References …………………………………………………………………………………………………….. 36

Chapter 2. Architecture and the UML…………………………………………………………………. 37 2.1 Architecture ……………………………………………………………………………………………… 37 2.2 Logical and Physical Architecture …………………………………………………………….. 38 2.3 The Five Views of Architecture…………………………………………………………………. 45 2.4 Implementing Architectures ……………………………………………………………………… 57 References …………………………………………………………………………………………………….. 63

Chapter 3. The Role of Design Patterns…………………………………………………………….. 65 3.1 Introduction………………………………………………………………………………………………. 65 3.2 The ROPES Development Process………………………………………………………….. 65 3.3 Design Pattern Basics ……………………………………………………………………………… 85 3.4 Using Design Patterns in Development ……………………………………………………. 89 References …………………………………………………………………………………………………….. 92

Part II: Architectural Design Patterns …………………………………………………………………….. 93 References …………………………………………………………………………………………………….. 94

Chapter 4. Subsystem and Component Architecture Patterns …………………………… 95 4.1 Layered Pattern ……………………………………………………………………………………….. 95 4.2 Five-Layer Architecture Pattern ……………………………………………………………….. 99 4.3 Microkernel Architecture Pattern…………………………………………………………….. 102 4.4 Channel Architecture Pattern …………………………………………………………………. 106 4.5 Recursive Containment Pattern ……………………………………………………………… 110 4.6 Hierarchical Control Pattern……………………………………………………………………. 115 4.7 Virtual Machine Pattern ………………………………………………………………………….. 118 4.8 Component-Based Architecture ……………………………………………………………… 124 4.9 ROOM Pattern ……………………………………………………………………………………….. 130 References …………………………………………………………………………………………………… 136

Chapter 5. Concurrency Patterns …………………………………………………………………….. 137 5.1 Introduction…………………………………………………………………………………………….. 137 5.2 Concurrency Pattern ………………………………………………………………………………. 137 5.3 Message Queuing Pattern ……………………………………………………………………… 139 5.4 Interrupt Pattern……………………………………………………………………………………… 143 5.5 Guarded Call Pattern ……………………………………………………………………………… 148 5.6 Rendezvous Pattern ………………………………………………………………………………. 153

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5.7 Cyclic Executive Pattern…………………………………………………………………………. 156 5.8 Round Robin Pattern ……………………………………………………………………………… 159 5.9 Static Priority Pattern ……………………………………………………………………………… 163 5.10 Dynamic Priority Pattern ………………………………………………………………………. 170 References …………………………………………………………………………………………………… 174

Chapter 6. Memory Patterns…………………………………………………………………………….. 176 6.1 Memory Management Patterns ………………………………………………………………. 176 6.2 Static Allocation Pattern …………………………………………………………………………. 176 6.3 Pool Allocation Pattern …………………………………………………………………………… 180 6.4 Fixed Sized Buffer Pattern ……………………………………………………………………… 185 6.5 Smart Pointer Pattern …………………………………………………………………………….. 189 6.6 Garbage Collection Pattern…………………………………………………………………….. 194 6.7 Garbage Compactor Pattern…………………………………………………………………… 199 References …………………………………………………………………………………………………… 204

Chapter 7. Resource Patterns ………………………………………………………………………….. 205 7.1 Introduction…………………………………………………………………………………………….. 205 7.2 Critical Section Pattern …………………………………………………………………………… 210 7.3 Priority Inheritance Pattern …………………………………………………………………….. 214 7.4 Highest Locker Pattern …………………………………………………………………………… 220 7.5 Priority Ceiling Pattern ……………………………………………………………………………. 225 7.6 Simultaneous Locking Pattern………………………………………………………………… 231 7.7 Ordered Locking Pattern ………………………………………………………………………… 236 References …………………………………………………………………………………………………… 241

Chapter 8. Distribution Patterns ……………………………………………………………………….. 242 8.1 Introduction…………………………………………………………………………………………….. 242 8.2 Shared Memory Pattern …………………………………………………………………………. 243 8.3 Remote Method Call Pattern ………………………………………………………………….. 248 8.4 Observer Pattern ……………………………………………………………………………………. 253 8.5 Data Bus Pattern ……………………………………………………………………………………. 258 8.6 Proxy Pattern …………………………………………………………………………………………. 267 8.7 Broker Pattern ………………………………………………………………………………………… 274 References …………………………………………………………………………………………………… 279

Chapter 9. Safety and Reliability Patterns………………………………………………………… 281 9.1 Introduction…………………………………………………………………………………………….. 281 9.2 Protected Single Channel Pattern ………………………………………………………….. 283 9.3 Homogeneous Redundancy Pattern ………………………………………………………. 287 9.4 Triple Modular Redundancy Pattern……………………………………………………….. 291 9.5 Heterogeneous Redundancy Pattern ……………………………………………………… 295 9.6 Monitor-Actuator Pattern ………………………………………………………………………… 299 9.7 Sanity Check Pattern ……………………………………………………………………………… 303 9.8 Watchdog Pattern…………………………………………………………………………………… 306 9.9 Safety Executive Pattern ………………………………………………………………………… 311 References …………………………………………………………………………………………………… 315

Appendix A. Notational Summary …………………………………………………………………….. 317 Class Diagram ……………………………………………………………………………………………… 317 Collaboration Diagram………………………………………………………………………………….. 321 Sequence Diagram ………………………………………………………………………………………. 322 Use Cases……………………………………………………………………………………………………. 323 Implementation Diagrams …………………………………………………………………………….. 324 Package diagram …………………………………………………………………………………………. 325 Statechart …………………………………………………………………………………………………….. 326 Activity Diagrams …………………………………………………………………………………………. 330

Appendix B. Pattern Index ……………………………………………………………………………….. 332

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Copyright Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and Addison-Wesley was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals.

The author and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein.

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Library of Congress Cataloging-in-Publication Data

Douglass, Bruce Powel.

Real-Time Design Patterns : robust scalable architecture for Real-time systems / Bruce Powel Douglass.

p. cm.—(The Addison-Wesley object technology series)

Includes bibliographical references and index.

(alk. paper)

1. Real-time data processing. 2. Software patterns. 3. Computer architecture.

I. Title. II. Series.

qa76.54 .D68 2003

004'.33—dc21

2002074701

vi

Copyright © 2003 by Pearson Education, Inc.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. Published simultaneously in Canada.

For information on obtaining permission for use of material from this work, please submit a written request to:

Pearson Education, Inc.

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75 Arlington Street, Suite 300

Boston, MA 02116

Fax: (617) 848-7047

Text printed on recycled paper

1 2 3 4 5 6 7 8 9 10—CRS—0605040302

First printing, September 2002

Dedication

For Sarah. With all my heart, I dedicate this book and the following haiku to you.

Mist cool forest mist subdued hues, shrouded souls walking, touching, sigh

Foreword In this book, Bruce Douglass illustrates for the first time how two important contemporary software engineering advances—patterns and the UML—can be applied advantageously to the concepts and techniques traditionally used in mainstream real-time software. Most other publications about software patterns (such as [1]) have not addressed real-time systems per se in any depth, or have focused on the narrower and more advanced topic of real-time middleware ([2]), or have been application domain specific ([3]).

This book offers a significant benefit to the practice of real-time computing, because software patterns and the UML enable potentially lower software costs in many systems. Real-time software spans the entire range of complexity and costs. In some real-time systems, the software is so small and simple, and the hardware is so complex and/or expensive, that software costs are a small fraction of the system costs (for example, software in a laser gyroscope). In other real-time systems, the software is so large and complex

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that regardless of the hardware costs, the software costs are a major part of the system costs (for example, software in a military or commercial aircraft). Barry Boehm, in his recent book updating the ubiquitous Cocomo software cost model [4], assigns an effort multiplier of 1.74 (the highest one) to all lifecycle phases of this latter kind of software, compared to "nominal" software (depending on the project circumstances, that multiplier can easily be a major underestimation). Most real-time software lies between these two extremes, and it is that mainstream audience of practitioners who will benefit the most from this book.

Historically, developers of real-time software have lagged behind other developers in using the most contemporary software engineering methodologies. There are several reasons for this.

One is, as mentioned above, that some real-time software is so simple that only the most elementary methodologies are needed.

A more common reason is that many real-time systems with non-trivial software suffer from hardware capacity constraints (due to size, weight, power, and so on). Software structured for purposes such as re- usability, modularity, or flexibility does tend to consume additional time or space resources. This is sometimes compensated for by the fact that commodity computing system hardware cost is always declining and its performance is always increasing. But in many real-time systems, hardware cost is still an easily measured quantitative factor that is thought to outweigh the hard-to-measure qualitative factors of software quality and costs.

Yet another reason is that real-time software practitioners are frequently application experts who are not always educated enough in modern software engineering to understand and employ it properly. New computer science and engineering graduates rarely enter the real-time field, because their formal education has not exposed them to much if any significant realistic real-time practice (real-time is a uniquely disadvantaged aspect of computer science and engineering in this respect), and what little real-time theory they may have learned is still of very limited practical relevance.

This book provides an introduction to software patterns and the UML—by one of the most authoritative contributors to those topics—as applied to mainstream real-time software, in a manner that is easily understood by practitioners in that field without prerequisite knowledge. Those who make a modest investment in learning this material can expect to discover how to cast much of their hard-earned professional experience in a framework that can make their real-time software designs more predictable— not just in terms of their timeliness (timeliness predictability being the raison d'être of real-time computing), but also in terms of their lifecycle costs.

Another prospective benefit for many real-time software designers of becoming familiar with software patterns and the UML is that these issues are of rapidly increasing importance to building larger scale, more dynamic and complex, and more distributed real-time computing systems. Such systems offer highly significant (albeit as yet not always fully appreciated) added value to many enterprises, and hence offer perhaps the most challenging and rewarding career development opportunities in the field of real-time computing systems. This book is an excellent starting point toward that future.

—E. Douglas Jensen Natick, Massachusetts July 2002

Doug Jensen is widely recognized as one of the pioneers of real-time computing systems, and especially of dynamic distributed real-time computing systems. He is credited with the research leading to the world's first deployed distributed real-time computer control system product. He has over three decades of hardware, software, and systems research and technology development experience in military and industrial real-time computing, and was on the faculty of the Computer Science Department of Carnegie Mellon University for eight years. He is currently in a senior technical leadership position at The MITRE Corporation, where he conducts research and technology transition on real-time computing systems for projects of strategic national interest. Doug Jensen's Web site is http://www.real-time.org.

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References

1. Boehm, Barry, Ellis Horowitz, Ray Madachy, Donald Reifer, Bradford Clark, Bert Steece, A. Winsor Brown, Sunita Chulani, and Chris Abts. Software Cost Estimation with Cocomo II. Upper Saddle River, NJ: Prentice Hall, January 2000.

2. Gamma, Erich, Richard Helm, Ralph Johnson, and John Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Reading, MA: Addison-Wesley, 1995.

3. Lea, Doug. Design Patterns for Avionics Control Systems, http://st- www.cs.uiuc.edu/users/patterns/patterns.html, 1994.

4. OOPSLA 2001, Workshop on Patterns in Distributed Real-Time and Embedded Systems, ACM, October 2001.

Preface Goals

Audience

Organization

More Information

Acknowledgments

Goals

Real-time and embedded systems (RTE systems) must execute in a much more constrained environment than "traditional" computer systems such as desktop and mainframe computers. RTE systems must be highly efficient, optimally utilizing their limited processor and memory resources, and yet must often outperform systems with significantly more compute power. In addition, many RTE systems have important safety-critical and high-reliability requirements because they are often used in systems such as avionics flight control, nuclear power plant control, life support and medical instrumentation. The creation of RTE systems to meet these functional and quality of service requirements requires highly experienced developers with decades of experience. Yet, over the years, these developers have encountered the same problems over and over—maybe not exactly the same problems but common threads. The very best developers abstract these problems and their solutions into generalized approaches that have proved consistently effective. These generalized approaches are called design patterns. They are often best applied at the level of the system or software architecture—the sum of design decisions that affect the fundamental organization of the system. Real-Time Design Patterns is an attempt to capture in one place a set of architectural design patterns that are useful in the development of RTE systems.

Audience

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The book is oriented toward the practicing professional software developer and the computer science major in the junior or senior year. This book could also serve as an undergraduate- or graduate-level text, but the focus is on practical development rather than a theoretical dissertation. The book assumes a reasonable proficiency in at least one programming language and a basic understanding of the fundamental concepts of object orientation, the Unified Modeling Language (UML), and real-time systems.

Organization

Part I consists of three chapters. Chapter 1 provides a very brief review of the major concepts in the Unified Modeling Language. Chapter 2 introduces the fundamental concepts of architecture as they are defined in the Rapid Object-oriented Process for Embedded Systems (ROPES), including the primary division of architecture into logical (design-time) and physical (run-time) aspects, and the five important architectural views. In the third chapter, the book gets into a discussion of design patterns and their role in defining architecture. Because it is difficult to discuss architecture in a process-free environment, the ROPES process, and the key technologies it tries to optimize, are introduced to provide a background in which design patterns may be effectively discussed. Once process has been introduced, design patterns are next. Their various aspects are explained, and the fundamental organization of design patterns used in this book is provided. The chapter finishes with a discussion of how design patterns can be applied in the development of real systems.

Part II contains the architectural design patterns that reify the ways that large-scale system components are organized and structured to optimize some set of general system criteria.

The patterns in Part II are organized around the architectural concept they address. Chapter 4 is dedicated to high-level structural patterns— focused around what is called the Subsystem or Component architecture. Because concurrency and resource management is so crucial to real-time and embedded systems, Chapter 5 focuses on the common patterns of concurrency. Memory management is crucial for many systems in this domain, and it is the subject of Chapter 6. We see even more general resource management patterns in Chapter 7. Chapter 8 presents a number of common distribution architecture patterns that define how objects can be distributed across multipl