并发与网络对象设计模式：构建现代中间件系统的关键模式

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"《Pattern-Oriented Software Architecture, Patterns for Concurrent and Networked Objects, Volume 2》是由Douglas Schmidt, Michael Stal, Hans Rohnert和Frank Buschmann合著的一本关于软件工程领域的设计模式专著。这本书专注于并发和网络化对象的设计模式，旨在帮助开发者构建现代面向对象的中间件系统。书中详细介绍了17个关键设计模式，并涵盖了服务访问、配置、事件处理、同步、并发等核心主题。" 在《Pattern-Oriented Software Architecture, Volume 2》中，作者深入探讨了以下几个方面的知识点： 1. **并发和网络化对象**：这部分内容讨论了在网络环境和多线程环境下，如何设计和实现对象以确保高效、可靠和可维护的代码。这包括如何处理异步通信、并发控制以及网络通信的挑战。 2. **服务访问和配置模式**：这些模式关注于如何优雅地提供服务接口，使客户端能够安全、灵活地访问服务。同时，也涉及如何管理服务的配置信息，使得系统的扩展和调整变得更加容易。 3. **事件处理模式**：书中详细阐述了如何设计事件驱动的架构，以处理系统中的异步事件。这包括事件发布/订阅模式、事件队列等，这些模式有助于提高系统的响应性和解耦度。 4. **同步模式**：这部分内容主要关注于在并发环境中如何保护共享资源，防止竞态条件和死锁的发生。书中可能会介绍互斥、信号量、条件变量等同步原语的使用方法。 5. **并发模式**：这部分深入研究了处理并发问题的策略，如工作窃取、线程池、读写锁等，这些模式可以有效提升多线程环境下的性能。 6. **模式的编织**：书中会展示如何将前面提到的模式组合在一起，形成一个完整的系统架构。这一章通常会给出一些实际案例，展示如何在实际项目中应用这些模式。 7. **模式的历史、现状与未来**：作者们回顾了设计模式的发展历程，分析了当前模式在软件开发中的地位，同时展望了未来可能出现的新模式和技术趋势。 8. **结论**：在书的结尾，作者可能提供了对整个主题的总结，强调了学习和应用这些模式的重要性，并给出了对未来软件工程师的建议。 9. **附录**：包含术语表、符号说明、参考文献以及模式索引，方便读者查阅和进一步学习。这本书是软件工程领域尤其是并发和网络编程方面的重要参考资料，适合软件设计师、架构师以及对并发编程感兴趣的开发者阅读。通过学习这些模式，开发者可以更好地理解和构建复杂的分布式系统。

We are also grateful for the support from colleagues and sponsors of our research on

patterns and the ACE and TAO middleware frameworks, notably the contributions of Ron

Akers (Motorola), Al Aho (Lucent), Steve Bachinsky (SAIC), Detlef Becker (Siemens), Jim

Blaine (Washington University), John Buttitto (Motorola), Becky Callison (Boeing), Wei

Chiang (Nokia), Russ Claus (NASA), Joe Cross (Lockheed Martin), Bryan Doerr (Boeing),

Karlheinz Dorn (Siemens), Sylvester Fernandez (Lockheed Martin), Andreas Geisler

(Siemens), Helen Gill (DARPA), Trey Grubbs (Raytheon), Jody Hagins (ATD), Andy Harvey

(Cisco), Thomas Heimke (Siemens), Kalai Kalaichelvan (Nortel), Arvind Kaushal (Motorola),

Steve Kay (Tellabs), Chandra Kintala (Lucent), Gary Koob (DARPA), Sean Landis

(Motorola), Rick Lett (Sprint), Joe Loyall (BBN), Mike Masters (NSWC), Ed Mays (US Marine

Corps), John Mellby (Raytheon), Dave Meyer (Virtual Technology), Eileen Miller (Lucent),

Stan Moyer (Telcordia), Russ Noseworthy (Object Sciences), Guru Parulkar (Cisco), Dan

Paulish (Siemens), James Plamondon (Microsoft), Dieter Quehl (Siemens), Lucie Robillard

(US Air Force), Allyn Romanow (Cisco), Rick Schantz (BBN), Steve Shaffer (Kodak), Dave

Sharp (Boeing), Naval Sodha (Ericsson), Brian Stacey (Nortel), Paul Stephenson (Ericsson),

Umar Syyid (Hughes), Dave Thomas (OTI), Lothar Werzinger (Krones), Shalini Yajnik

(Lucent), and Tom Ziomek (Motorola).

Very special thanks go to Steve Rickaby, our copy editor, for enhancing our written material.

In addition, we thank our editor, Gaynor Redvers-Mutton, and everyone else at John Wiley &

Sons who made it possible to publish this book. This is the second book fostered by Gaynor

and Steve. Their support has been superb and we look forward to working with them on

forthcoming POSA volumes.

Finally, we would like to express our deepest gratitude to the late Richard Stevens, whose

seminal books inspired us to explore the wonders of network programming so many years

ago. His spirit pervades this book.

Guide to the Reader

"Cheshire-Puss will you tell me, please, which way I ought to go from here?"

"That depends a good deal on where you want to get to," said the Cat.

"I don't much care where—," said Alice.

"Then it doesn't matter which way you go," said that cat.

"—so long as I get somewhere" Alice added as an explanation.

"Oh, you're sure to do that," said the Cat, "if you only walk long enough."

Louis Carroll, "Alice in Wonderland"

This book is structured so you can read it cover-to-cover. If you know where you want to get

to, however, you may want to choose your own route through the book. In this case, the

following hints can help you decide which topics to focus upon and the order in which to read

them.

Introduction to Patterns

If this book is your initial exposure to patterns, we suggest you first read the introduction to

patterns in [POSA1] and [GoF95], which explore the concepts and terminology related to

patterns for software architectures and designs. In particular, all the patterns presented in

this book build upon the conceptual foundation for patterns specified in [POSA1]:

§ The definition of patterns for software architectures

§ The categorization of these patterns into architectural patterns, design patterns, and

idioms

[1]

and

§ The pattern description format

Moreover, the implementations of many patterns in this book are enhanced by using

patterns from [POSA1] and [GoF95]. To guide the application of the patterns in production

software development projects we therefore suggest you keep all three books handy.

[1]

See the Glossary for a definition of these pattern categories.

Structure and Content

The first chapter in this book, Concurrent and Networked Objects, describes the key

challenges of designing concurrent and networked systems. It also outlines the scope and

context for the patterns we present. Finally, it presents a case study that applies eight

patterns in this book to develop a concurrent Web server.

Sixteen pattern descriptions and one idiom form the main part of this book. We group them

into four chapters, corresponding to key problem areas—service access and configuration,

event handling, synchronization and concurrency—in the development of concurrent and

networked middleware and applications. The order in which you read this material is up to

you. One approach is to read important core patterns first:

§ The Wrapper Facade design pattern (47)

[2]

§ The Reactor architectural pattern (179)

§ The Acceptor-Connector design pattern (285)

§ The Active Object design pattern (369)

The other twelve patterns and one idiom in the book are arranged to minimize forward

references. You can read them in any order of course, and we provide page numbers for

following references to other patterns within the book. This material completes and

complements the concepts defined by the four patterns listed above and covers a range of

issues relevant to designing and implementing concurrent and networked objects effectively.

You can also use this book to find solutions to problems you encounter in your projects. Use

the overview of our patterns in Chapter 6, Weaving the Patterns Together, to guide your

search, then locate in Chapters 2 through 5 the detailed descriptions of the patterns you

select as potential solutions.

No pattern is an island, completely separated from other patterns. Therefore, Chapter 6,

Weaving the Patterns Together, also describes how all the patterns in this book can be

woven together to form a pattern language for building networked applications and

middleware. If you want an overall perspective of the patterns in this book before delving into

the individual patterns, we recommend you skim the pattern language presentation in

Chapter 6 before reading the patterns in Chapters 2 through 5 in depth.

Chapter 7, The Past, Present, and Future of Patterns and Chapter 8, Concluding Remarks

complete the main content of this book. The remainder of the book consists of a glossary of

technical terms, an overview of the notations used in the figures, references to related work,

and an index of patterns, topics, and names.

[2]

We adopt the page number notation introduced by [GoF95]. (47) means that the

corresponding pattern description starts on page 47.

Pattern Form

All patterns presented in this book are self-contained, following the [POSA1] pattern form.

This form allows us to present both the essence and the key details of a pattern. Our goal is

to serve readers who simply want an overview of the pattern's fundamental ideas, as well as

those who want to know how the patterns work in depth.

Each section in our pattern form sets the stage for the subsequent section. For instance, the

Example section introduces the Context, Problem, and Solution sections, which summarize

a pattern's essence. The Solution section foreshadows the Structure and Dynamics section,

which then present more detailed information about how a pattern works, preparing readers

for the Implementation section.

The Example Resolved, Variants, Known Uses, Consequences and See Also sections

complete each pattern description. We include extensive cross-references to help you to

understand the relationships between the patterns in this book and other published patterns.

To anchor the presentation of a pattern's implementation activities to production software

systems, much of the sample code is influenced by components provided in the ACE

framework [Sch97]. If you first want to get an overview of all the patterns you may therefore

want to skip over the Implementation sections on your initial pass through the book and

come back to them when you need to know a particular pattern's implementation details.

Although the pattern form we use in this book incurs some repetition within the pattern

descriptions, we have found that this repetition helps readers navigate through the

descriptions more effectively by minimizing 'back-tracking'.

Chapter 1: Concurrent and Networked Objects

Overview

"With the exception of music, we have been trained to think of patterns as

fixed affairs. It's easier and lazier that way, but, of course, all nonsense. The

right way to begin to think of the pattern which connects is to think of a

dance of interacting parts, pegged down by various sorts of limits."

Gregory Bateson — Cultural Anthropologist

This chapter introduces topics related to concurrent and networked objects. We first motivate

the need for advanced software development techniques in this area. Next, we present an

overview of key design challenges faced by developers of concurrent and networked object-

oriented applications and middleware. To illustrate how patterns can be applied to resolve

these problems, we examine a case study of an object-oriented framework and a high-

performance Web server implemented using this framework. In the case study we focus on

key patterns presented in this book that help to simplify four important aspects of concurrent

and networked applications:

§ Service access and configuration

§ Event handling

§ Synchronization and

§ Concurrency

1.1 Motivation

During the past decade advances in VLSI technology and fiber-optics have increased

computer processing power by 3–4 orders of magnitude and network link speeds by 6–7

orders of magnitude. Assuming that these trends continue, by the end of this decade

§ Desktop computer clock speeds will run at ~100 Gigahertz

§ Local area network link speeds will run at ~100 Gigabits/second

§ Wireless link speeds will run at ~100 Megabits/second and

§ The Internet backbone link speeds will run at ~10 Terabits/second

Moreover, there will be billions of interactive and embedded computing and communication

devices in operation throughout the world. These powerful computers and networks will be

available largely at commodity prices, built mostly with robust common-off-the-shelf (COTS)

components, and will inter-operate over an increasingly convergent and pervasive Internet

infrastructure.

To maximize the benefit from these advances in hardware technology, the quality and

productivity of technologies for developing concurrent and networked middleware and

application software must also increase. Historically, hardware has tended to become

smaller, faster, and more reliable. It has also become cheaper and more predictable to

develop and innovate, as evidenced by 'Moore's Law'. In contrast, concurrent and networked

software has often grown larger, slower, and more error-prone. It has also become very

expensive and time-consuming to develop, validate, maintain, and enhance.

Although hardware improvements have alleviated the need for some low-level software

optimizations, the lifecycle cost [Boe81] and effort required to develop software—particularly

mission-critical concurrent and networked applications—continues to rise. The disparity

between the rapid rate of hardware advances versus the slower software progress stems

from a number of factors, including:

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