Multithreading gives developers using the Java 2 platform a powerful tool for dramatically improving the responsiveness and performance of their programs on any platform, even those without inherent multithreading support. Multithreaded Programming with Java Technology is the first complete guide to multithreaded development with the Java 2 platform. Multithreading experts Bil Lewis and Daniel J. Berg cover the underlying structures upon which threads are built; thread construction; and thread lifecycles, including birth, life, death, and cancellation. Next, using extensive code examples, they cover everything developers need to know to make the most of multithreading, including:
Powerful techniques and comprehensive example code for improving Java-based application performance with multithreading!
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Background: Traditional Operating Systems. What Is a Thread? Kernel Interaction. Concurrency vs Parallelism. System Calls. Signals. Synchronization. Scheduling. The Value of Using Threads. Parallelism. Throughput. Responsiveness. Communications. System Resources. Distributed Objects. Same Binary for Uniprocessors and Multiprocessors. Program Structure. What Kinds of Programs to Thread. Inherently MT Programs. Not Obviously MT Programs. Automatic Threading. Programs Not to Thread. What About Shared Memory? Threads Standards. Performance. Operating Systems. NFS. SPECfp 95. SPECint_rate95. Java Benchmarks.
Implementation vs Specification. Thread Libraries. The Process Structure. Lightweight Processes. Threads and LWPs. The POSIX Multithreaded Model. System Calls. Signals.
Thread Lifecycle. Exiting a Thread. The Runnable Interface. Waiting for Threads. Who Am I? Exiting the Process. Suspending a Thread. Cancellation. ThreadDeath. Garbage Collecting Threads. Zombies. Is She Still Alive? Restarting Threads. An Example: Create and Join. APIs Used in This Chapter. The Class java.lang.Thread. The Class Extensions.InterruptibleThread. The Interface java.lang.Runnable.
Different Models of Kernel Scheduling. Many Threads on One LWP. One Thread per LWP. Many Threads on Many LWPs (Strict). The Two-Level Model. Thread Scheduling. Process Contention Scope. System Contention Scope. Context Switching. Preemption. How Many LWPs? How to Get Those LWPs in Java. Changing Scheduling Parameters for LWPs. Realtime LWPs. Allocation Domains. Binding LWPs to Processors. Java Scheduling Summary. When Should You Care About Scheduling? APIs Used in This Chapter. The Class java.lang.Thread.
Synchronization Issues. Atomic Actions and Atomic Instructions. Critical Sections. Lock Your Shared Data! Synchronization Variables. Mutexes. Semaphores. Condition Variables. Java wait/notify. InterruptedException. Controlling the Queue Length. POSIX-Style Synchronization in Java. APIs Used in This Chapter. The Class java.lang.Object. The Class Extensions.Semaphore. The Class Extensions.Mutex. The Class Extensions.ConditionVar.
Complex Locking Primitives. Readers/Writer Locks. Priority Inheritance Mutexes. FIFO Mutexes. Recursive Mutexes. Nonblocking Synchronization. Spin Locks. Timeouts. Elvis and the UFOs. Other Synchronization Variables. Join. Barriers. Single Barriers. Win32 Event Objects. Win32 Critical Sections. Multiple Wait Semaphores. Interlocked Instructions. Message Queues. Win32 I/O Completion Ports. Communicating via Streams. Volatile. Performance. Condition Variables vs wait/notify. Coarse vs Fine Grain Locking. What to Lock. Double-Checked Locking. Synchronization Problems. Deadlocks. Race Conditions. Recovering from Deadlocks. The Lost Wakeup. InterruptedException. APIs Used in This Chapter. The Class Extensions.RWLock. The Class Extensions.Barrier. The Class Extensions.SingleBarrier.
Thread-Specific Data. Java TSD. APIs Used in This Chapter. The Class java.lang.ThreadLocal.
What Cancellation Is. Polling for Cancellation. Asynchronous Cancellation. Deferred Cancellation. Using interrupt() for Deferred Cancellation. Progressive Shutdown. interrupt( ). Don't Call stop(). ThreadDeath. Using stop() to Implement Thread.exit(). Never Exit a Thread! Defined Cancellation/Interruption Points. Not Cancelling upon Interruption. Handling Interrupts. Cancellation State. A Cancellation Example. Using Cancellation. Ensuring Bounded CPU Time. Interrupting Sleeping Threads. The Morning After. Cleanup. Implementing enableInterrupts( ). A Cancellation Example (Improved). Simple Polling. APIs Used in This Chapter. The Class java.lang.Thread. The Class Extensions.InterruptibleThread.
Thread Groups. Thread Security. Real-World Examples. General Tips and Hints. Daemon Threads. Daemon Thread Groups. Calling Native Code. A Few Assorted Methods. Stack Size. Deprecated Methods. The Effect of Using a JIT. Adaptive Compilers. APIs Used in This Chapter. The Class java.lang.Thread. The Class java.lang.ThreadGroup.
The Native Threads Libraries. Multithreaded Kernels. Symmetric Multiprocessing. Are Libraries Safe? Window Systems. Working with Unsafe Libraries. When Should a Class Be Synchronized? Synchronized Collections in Java 2. Java's Multithreaded Garbage Collector.
Making Libraries Safe and Hot. Making malloc() More Concurrent. Manipulating Lists. Single, Global Mutex. Global RWLock with Global Mutex to Protect Salaries. Global RWLock with Local Mutex to Protect Salaries. One Local Lock. Two Local Locks. Local RWLock with Local Mutex to Protect Salaries. Program Design. Design Patterns.
Remote Method Invocation. Sending Remote References. RMI's Use of Threads. The Deadlock Problem with RMI. Remote Garbage Collection.
Static Lock Analyzer. Using a Thread-Aware, Graphical Debugger. Proctool. TNFview.
Optimization: Objectives and Objections. CPU Time, I/O Time, Contention, Etc. CPU. Memory Latency. Memory Bandwidth. I/O Latency. Contention. Throughput vs Latency. Limits on Speedup. Amdahl's Law. Performance Bottlenecks. Benchmarks and Repeatable Testing. Is It Really Faster? General Performance Optimizations. Thread-Specific Performance Optimizations. Dealing with Many Open Sockets. The Lessons of NFS.
Types of Multiprocessors. Shared Memory Symmetric Multiprocessors. Bus Architectures. LoadLocked/StoreConditional and Compare and Swap. Volatile: The Rest of the Story. Memory Systems. Reducing Cache Misses.
Threads and Windows. Displaying Things for a Moment (Memory.java). Socket Server (Master/Slave Version). Socket Server (Producer/Consumer Version). Making a Native Call to pthread_setconcurrency( ). Actual Implementation of POSIX Synchronization. A Robust, Interruptible Server. Disk Performance with Java. Other Programs on the Web.
Threads Newsgroup. Code Examples. Vendor's Threads Pages. Threads Research. Freeware Tools. Other Pointers. The Authors on the Net.
Threads Books. Related Books.
Function Descriptions. The Class java.lang.Thread. The Interface java.lang.Runnable. The Class java.lang.Object. The Class java.lang.ThreadLocal. The Class java.lang.ThreadGroup. Helper Classes from Our Extensions Library. The Class Extensions.InterruptibleThread. The Class Extensions.Semaphore. The Class Extensions.Mutex. The Class Extensions.ConditionVar. The Class Extensions.RWLock. The Class Extensions.Barrier. The Class Extensions.SingleBarrier. Glossary.
Today, there are three primary sets of multithreading (MT) libraries: the POSIX threads library, the Win32 threads library (both native), and Java. Although the APIs and implementations differ significantly, the fundamental concepts are the same. The ideas in this book are valid for all three; the details of the APIs differ.
All the specific discussion in this book focuses on the Java multithreading model, with comparisons to POSIX and Win32 throughout. Java threads are always implemented upon a lowlevel library which does the real work. Hence Java on UNIX is generally based on POSIX, while Java on NT will be based on Win32 threads.
Because these lowerlevel libraries have so much impact on the actual performance of a Java program, we will devote significant attention to the native libraries. Because POSIX threads are more primitive than Win32 threads, they will be our basis of comparison and explanation. This allows us to explain the inner workings of threads before jumping to the more intricate workings of Java.
A frank note about our motivation is in order here. We have slaved away for countless hours on this book because we're propellerheads who honestly believe that this technology is a superb thing and that the widespread use of it will make the world a better place for hackers like ourselves.
Your motivations for writing MT programs? You can write your programs better and more easily, they'll run faster, you'll get them to market more quickly, they'll have fewer bugs, and you'll have happier programmers, customers, and higher sales. The only losers in this game are the competitors, who will lag behind you in application speed and quality.
MT is here today. It is now ubiquitous. As a professional programmer, you have an obligation to understand this technology. It may or may not be appropriate for your current project, but you must be able to make that conclusion yourself. This book will give you what you need to make that decision.
Welcome to the world of the future!Who Should Use This Book
This book aims to give the programmer or technical manager a solid understanding of threadswhat they are, how they work, why they are useful, and some of the programming issues surrounding their use. As an introductory text, it does not attempt a deep, detailed analysis of the most current research, but it does come close. After reading this book the reader should have a solid understanding of the fundamentals, be able to write credible, modestly complex, threaded programs, and have the understanding necessary to analyze their own programs and determine the viability of threading them.
This book has been written with the experienced Java programmer in mind. There is a definite UNIX bias, but none of that is essential to understanding. A Java programmer who does not know C will find the POSIX code fragments mildly challenging, although possible to decipher. The concepts should be clear. A technically minded nonprogrammer should be able to follow most of the concepts and understand the value of threads. A nontechnical person will not get much from this book.
This book does not attempt to explain the use of Win32 or POSIX APIs. It does contrast them to Java APIs to explain some of the higherlevel Java behavior in lowerlevel terms.How This Book Is Organized
Chapter 1, IntroductionIn which we discuss the motivation for creating thread libraries, the advent of shared memory multiprocessors, and the interactions between threads and SMP machines.
Chapter 2, ConceptsIn which the reader is introduced to the basic concepts of multitasking operating systems and of multithreading as it compares to other programming paradigms. The reader is shown reasons why multithreading is a valuable addition to programming paradigms, and a number of examples of successful deployment are presented.
Chapter 3, FoundationsIn which we introduce the reader to the underlying structures upon which threads are built, the construction of the thread itself, and the operating system support that allows efficient implementation.
Chapter 4, LifecycleIn which the reader is treated to a comprehensive explanation of the intricacies in the life of a threadbirth, life, and deatheven death by vile cancellation. A small program that illustrates all these stages concludes the chapter.
Chapter 5, SchedulingIn which we explain the myriad details of various scheduling models and alternative choices that could be made, describe context switching in detail, and delve into gruesome detail on various design options. There is light at the end of the tunnel, however.
Chapter 6, SynchronizationIn which the reader is led on a hunt for the intimidating synchronization variable and discovers that it is not actually as frightening as had been thought. Programs illustrating the basic use of the POSIX and Java primitives are shown.
Chapter 7, ComplexitiesIn which a series of more complex synchronization variables and options are presented and the tradeoff between them and the simpler ones are discussed. Synchronization problems and techniques for dealing with them conclude the chapter.
Chapter 8, TSDIn which explanations of threadspecific data, their use, and some implementation details are provided.
Chapter 9, CancellationIn which we describe the acrimonious nature of some programs and how unwanted threads may be disposed of. The highly complex issues surrounding bounded time termination and program correctness are also covered. A simple conclusion is drawn.
Chapter 10, DetailsIn which a number of minor details are covered.
Chapter 11, LibrariesIn which we explore a variety of operating systems issues that bear heavily upon the usability of threads in actual programs. We examine the status of library functions and the programming issues facing them. We look at some design alternatives for library functions.
Chapter 12, DesignIn which we explore some designs for programs and library functions. Making both programs and individual functions more concurrent is a major issue in the design of these functions. We look at a variety of code examples and the tradeoffs between them.
Chapter 13, RMIIn which we examine RMI and see what it provides in terms of a distributed object programming model. We look at how threading interacts with it and how it uses threads.
Chapter 14, ToolsIn which we consider the kinds of new tools that a reader would want when writing a threaded program. An overview of the Solaris tool set is given, as representative of what should be looked for.
Chapter 15, PerformanceIn which we make things faster, look at general performance issues, political performance issues, and thread specific performance issues. We conclude with a discussion of the actual performance of multithreaded NFS.
Chapter 16, HardwareIn which we look at the various designs for SMP machines (cache architectures, interconnect topologies, atomic instructions, invalidation techniques) and consider how those designs affect our programming decisions. Some optimization possibilities are looked at.
Chapter 17, ExamplesIn which several complete programs are presented. The details and issues surrounding the way they use threads are discussed, and references to other programs on the Net are made.