Pro.NET 4 Parallel Programming in C#

Transcription

1 Pro.NET 4 Parallel Programming in C# Adam Freeman

2 Pro.NET 4 Parallel Programming in C# Copyright 2010 by Adam Freeman All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior written permission of the copyright owner and the publisher. ISBN-13 (pbk): ISBN-13 (electronic): Printed and bound in the United States of America Trademarked names may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, we use the names only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. President and Publisher: Paul Manning Lead Editor: Ewan Buckingham Technical Reviewer: André van Meulebrouck Editorial Board: Clay Andres, Steve Anglin, Mark Beckner, Ewan Buckingham, Gary Cornell, Jonathan Gennick, Jonathan Hassell, Michelle Lowman, Matthew Moodie, Duncan Parkes, Jeffrey Pepper, Frank Pohlmann, Douglas Pundick, Ben Renow-Clarke, Dominic Shakeshaft, Matt Wade, Tom Welsh Coordinating Editor: Anne Collett Copy Editor: Heather Lang Production Support: Patrick Cunningham Indexer: BIM Indexing & Proofreading Services Artist: April Milne Cover Designer: Anna Ishchenko Distributed to the book trade worldwide by Springer-Verlag New York, Inc., 233 Spring Street, 6th Floor, New York, NY Phone SPRINGER, fax , orders-ny@springer-sbm.com, or visit For information on translations, please rights@apress.com, or visit Apress and friends of ED books may be purchased in bulk for academic, corporate, or promotional use. ebook versions and licenses are also available for most titles. For more information, reference our Special Bulk Sales ebook Licensing web page at The information in this book is distributed on an as is basis, without warranty. Although every precaution has been taken in the preparation of this work, neither the author(s) nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in this work. The source code for this book is available to readers at You will need to answer questions pertaining to this book in order to successfully download the code.

3 For my wife Jacqui Griffyth and her chickens

4 Contents at a Glance About the Author... xiii About the Technical Reviewer... xiv Acknowledgments... xv Chapter 1: Introducing Parallel Programming... 1 Chapter 2: Task Programming... 7 Chapter 3: Sharing Data Chapter 4: Coordinating Tasks Chapter 5: Parallel Loops Chapter 6: Parallel LINQ Chapter 7: Testing and Debugging Chapter 8: Common Parallel Algorithms Index iv

5 Contents About the Author... xiii About the Technical Reviewer... xiv Acknowledgments... xv Chapter 1: Introducing Parallel Programming... 1 Introducing.NET Parallel Programming... 1 What s in This Book (and What Is Not)... 2 Understanding the Benefits (and Pitfalls) of Parallel Programming... 3 Considering Overhead... 3 Coordinating Data... 3 Scaling Applications... 3 Deciding When to Go Parallel... 3 Deciding When to Stay Sequential... 4 Getting Prepared for This Book... 4 Understanding the Structure of This Book... 4 Getting the Example Code... 5 Summary... 6 v

6 CONTENTS Chapter 2: Task Programming... 7 Hello Task... 7 Creating and Starting Tasks... 8 Creating Simple Tasks... 9 Setting Task State Getting a Result Specifying Task Creation Options Identifying Tasks Cancelling Tasks Monitoring Cancellation by Polling Monitoring Cancellation with a Delegate Monitoring Cancellation with a Wait Handle Cancelling Several Tasks Creating a Composite Cancellation Token Determining If a Task Was Cancelled Waiting for Time to Pass Using a Cancellation Token Wait Handle Using Classic Sleep Using Spin Waiting Waiting for Tasks Waiting for a Single Task Waiting for Several Tasks Waiting for One of Many Tasks Handling Exceptions in Tasks Handling Basic Exceptions Using an Iterative Handler Reading the Task Properties Using a Custom Escalation Policy vi

7 CONTENTS Getting the Status of a Task Executing Tasks Lazily Understanding Common Problems and Their Causes Task Dependency Deadlock Local Variable Evaluation Excessive Spinning Summary Chapter 3: Sharing Data The Trouble with Data Going to the Races Creating Some Order Executing Sequentially Executing Immutably Executing in Isolation Synchronizing Execution Defining Critical Regions Defining Synchronization Primitives Using Synchronization Wisely Using Basic Synchronization Primitives Locking and Monitoring Using Interlocked Operations Using Spin Locking Using Wait Handles and the Mutex Class Configuring Interprocess Synchronization Using Declarative Synchronization Using Reader-Writer Locks vii

8 CONTENTS Working with Concurrent Collections Using.NET 4 Concurrent Collection Classes Using First-Generation Collections Using Generic Collections Common Problems and Their Causes Unexpected Mutability Multiple Locks Lock Acquisition Order Orphaned Locks Summary Chapter 4: Coordinating Tasks Doing More with Tasks Using Task Continuations Creating Simple Continuations Creating One-to-Many Continuations Creating Selective Continuations Creating Many-to-One and Any-To-One Continuations Canceling Continuations Waiting for Continuations Handling Exceptions Creating Child Tasks Using Synchronization to Coordinate Tasks Barrier CountDownEvent ManualResetEventSlim AutoResetEvent SemaphoreSlim viii

9 CONTENTS Using the Parallel Producer/Consumer Pattern Creating the Pattern Combining Multiple Collections Using a Custom Task Scheduler Creating a Custom Scheduler Using a Custom Scheduler Common Problems and Their Causes Inconsistent/Unchecked Cancellation Assuming Status on Any-To-One Continuations Trying to Take Concurrently Reusing Objects in Producers Using BlockingCollection as IEnumerable Deadlocked Task Scheduler Summary Chapter 5: Parallel Loops Parallel vs. Sequential Loops The Parallel Class Invoking Actions Using Parallel Loops Setting Parallel Loop Options Breaking and Stopping Parallel Loops Handling Parallel Loop Exceptions Getting Loop Results Canceling Parallel Loops Using Thread Local Storage in Parallel Loops Performing Parallel Loops with Dependencies Selecting a Partitioning Strategy Creating a Custom Partitioning Strategy ix

10 CONTENTS Common Problems and Their Causes Synchronization in Loop Bodies Loop Body Data Races Using Standard Collections Using Changing Data Summary Chapter 6: Parallel LINQ LINQ, But Parallel Using PLINQ Queries Using PLINQ Query Features Ordering Query Results Performing a No-Result Query Managing Deferred Query Execution Controlling Concurrency Forcing Parallelism Limiting Parallelism Forcing Sequential Execution Handling PLINQ Exceptions Cancelling PLINQ Queries Setting Merge Options Using Custom Partitioning Using Custom Aggregation Generating Parallel Ranges x

11 CONTENTS Common Problems and Their Causes Forgetting the PLINQ Basics Creating Race Conditions Confusing Ordering Sequential Filtering Summary Chapter 7: Testing and Debugging Making Things Better When Everything Goes Wrong Measuring Parallel Performance Using Good Coding Strategies Making Simple Performance Comparisons Performing Parallel Analysis with Visual Studio Finding Parallel Bugs Debugging Program State Handling Exceptions Detecting Deadlocks Summary Chapter 8: Common Parallel Algorithms Sorting, Searching, and Caching Using Parallel Quicksort Traversing a Parallel Tree Searching a Parallel Tree Using a Parallel Cache Using Parallel Map and Reductions Using a Parallel Map Using a Parallel Reduction Using Parallel MapReduce xi

12 CONTENTS Speculative Processing Selection Speculative Caching Using Producers and Consumers Decoupling the Console Class Creating a Pipeline Index xii

13 About the Author Adam Freeman is an experienced IT professional who has held senior positions in a range of companies, most recently chief technology officer and chief operating officer of a global bank. He has written several of books on Java and.net and has a long-term interest in all things parallel. xiii

14 About the Technical Reviewer André van Meulebrouck has an interest in functional programming and the functional approach to parallel computing. He has written white papers and articles on functional programming and theoretical computer science and is a beta tester for F#, which is Microsoft s new functional programming language. He lives in southern California and works as a.net developer. xiv

15 Acknowledgments I would like to thank everyone at Apress for working so hard to bring this book to print. In particular, I would like to thank Anne Collett for keeping things on track and Ewan Buckingham for commissioning and editing the book. I would also like to thank Heather Lang and André van Meulebrouck whose respective efforts as copy editor and technical reviewer made this book far better than it would have been without them. xv