Programming with Posix Threads

Programming with POSIX Threads

David R. Butenhof

ADDISON-WESLEY

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Trademark acknowledgments:

UNIX is a registered trademark in the United States and other countries, licensed exclusively

through X/Open Company Ltd. Digital, DEC, Digital UNIX, DECthreads, VMS, and OpenVMS

are trademarks of Digital Equipment Corporation. Solaris, SPARC, SunOS, and Sun are

trademarks of Sun Microsystems Incorporated. SGI and IRIX are trademarks of Silicon Graphics,

Incorporated. HP-UX is a trademark of Hewlett-Packard Company. AIX, IBM, and OS/2 are

trademarks or registered trademarks of the IBM Corporation. X/Open is a trademark of X/Open

Company Ltd. POSIX is a registered trademark of the Institute of Electrical and Electronics

Engineers, Inc.

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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digital computers--Programming. I. Title. II. Series.

QA76.76.T55B88 1997

005.4'32--dc21

97-6635

CIP

Copyright 1997 by Addison Wesley Longman, 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.

To Anne, Amy,

and

Alyssa.

Quote acknowledgment:

American Heritage Dictionary of the English Language: page 1.

ISO/IEC 9945-1:1996, ?1996 by IEEE: page 29.

_______________________________________________________________________________

The White Rabbit put on his spectacles,

"Where shall I begin, please your Majesty?" he asked.

"Begin at the beginning," the King said, very gravely,

"and go on till you come to the end: then stop."

--Lewis Carroll, Alice's Adventures in Wonderland

are more friendly to users, that run blazingly fast on multiprocessors, and that may even be easier

to maintain. To accomplish all this, you need only add some relatively simple function calls to

your code, adjust to a new way of thinking about programming, and leap over a few yawning

chasms. Reading this book carefully will, I hope, help you to accomplish all that without losing

your sense of humor.

The threads model used in this book is commonly called "Pthreads," or "POSIX threads." Or,

more formally (since you haven't yet been properly introduced), the POSIX 1003. lc-1995

standard. I'll give you a few other names later--but for now, "Pthreads" is all you need to worry

about.

Pthreads interfaces are included with Sun's Solaris; Hewlett-Packard's Tru64 UNIX,

toward using them productively is understanding concurrency, synchronization, and scheduling.

The rest is (more or less) a matter of syntax and style, and an experienced thread programmer can

adapt to any of these models.

The threaded model can be (and has been) applied with great success to a wide range of

programming problems. Here are just a few:

 Large scale, computationally intensive programs

 High-performance application programs and library code that can take advantage of

multiprocessor systems

 Library code that can be used by threaded application programs

 Realtime application programs and library code

Intended audience

This book assumes that you are an experienced programmer, familiar with developing code

for an operating system in "the UNIX family" using the ANSI C language. I have tried not to

assume that you have any experience with threads or other forms of asynchronous programming.

The Introduction chapter provides a general overview of the terms and concepts you'll need for the

rest of the book. If you don't want to read the Introduction first, that's fine, but if you ever feel like

you're "missing something" you might try skipping back to get introduced.

Along the way you'll find examples and simple analogies for everything. In the end I hope

that you'll be able to continue comfortably threading along on your own. Have fun, and "happy

About the author

expected a standards meeting to be a formal and stuffy environment. As a result of this

misunderstanding, I was forced to rent ski equipment instead of using my own.

After the Pthreads standard went into balloting, I worked on additional thread

synchronization interfaces and multiprocessor issues with several POSIX working groups. I also

helped to define the Aspen threads extensions, which were fast tracked into X/Open XSH5.

I have worked at Digital Equipment Corporation for (mumble, mumble) years, in various

locations throughout Massachusetts and New Hampshire. I was one of the creators of Digital’s

own threading architecture, and I designed (and implemented much of) the Pthreads interfaces on

Digital UNIX 4.0. I have been helping people develop and debug threaded code for more than

eight years.

Acknowledgments

No project such as this book can truly be accomplished by a single person, despite the fact

that only one name appears on the cover. I could have written a book about threads without any

help--I know a great deal about threads, and I am at least reasonably competent at written

communication. However, the result would not have been this book, and this book is better than

that hypothetical work could possibly have been.

Thanks first and foremost to my manager Jean Fullerton, who gave me the time and

encouragement to write this book on the job--and thanks to the rest of the DECthreads team who

kept things going while I wrote, including Brian Keane, Webb Scales, Jacqueline Berg, Richard

Love, Peter Portante, Brian Silver, Mark Simons, and Steve Johnson.

Thanks to Garret Swart who, while he was with Digital at the Systems Research Center, got