Programming with POSIX Threads

Here is a programmer's guide to using and programming POSIX threads, commonly known as Pthreads. A "coder's book", this title tells how to use Pthreads in the real world, making efficient and portable applications. Pthreads are an important set of current tools programmers need to have in today's network-intensive climate.

David R. Butenhof, a recognized Pthreads authority, was deeply involved in the creation of the IEEE POSIX standard as well as the X/Open threading extensions, which were fast-tracked into X/Open XSH5 (UNIX98). An engineer at Digital Equipment Corporation, he was the lead architect and developer of Digital's own threading architecture and designed and implemented much of the Pthreads interfaces on Digital UNIX 4.0.

0201633922AB04062001

List of Example Programs

xii

(3)

Preface

xv

Intended audience

xvi

(1)

About the author

xvi

(1)

Acknowledgments

xvii

1 Introduction

1

(34)

1.1 The "bailing programmers"

3

(1)

1.2 Definitions and terminology

4

(4)

1.2.1 Asynchronous

4

(1)

1.2.2 Concurrency

4

(1)

1.2.3 Uniprocessor and multiprocessor

5

(1)

1.2.4 Parallelism

5

(1)

1.2.5 Thread safety and reentrancy

6

(1)

1.2.6 Concurrency control functions

7

(1)

1.3 Asynchronous programming is intuitive

8

(4)

1.3.1 ...because UNIX is asynchronous

9

(2)

1.3.2 ...because the world is asynchronous

11

(1)

1.4 About the examples in this book

12

(1)

1.5 Asynchronous programming, by example

13

(7)

1.5.1 The baseline, synchronous version

14

(1)

1.5.2 A version using multiple processes

15

(2)

1.5.3 A version using multiple threads

17

(2)

1.5.4 Summary

19

(1)

1.6 Benefits of threading

20

(5)

1.6.1 Parallelism

20

(2)

1.6.2 Concurrency

22

(2)

1.6.3 Programming model

24

(1)

1.7 Costs of threading

25

(3)

1.7.1 Computing overhead

26

(1)

1.7.2 Programming discipline

26

(1)

1.7.3 Harder to debug

27

(1)

1.8 To thread or not to thread?

28

(1)

1.9 POSIX thread concepts

29

(6)

1.9.1 Architectural overview

30

(1)

1.9.2 Types and interfaces

30

(1)

1.9.3 Checking for errors

31

(4)

2 Threads

35

(10)

2.1 Creating and using threads

35

(4)

2.2 The life of a thread

39

(6)

2.2.1 Creation

40

(1)

2.2.2 Startup

41

(1)

2.2.3 Running and blocking

42

(1)

2.2.4 Termination

43

(1)

2.2.5 Recycling

44

(1)

3 Synchronization

45

(52)

3.1 Invariants, critical sections, and predicates

45

(2)

3.2 Mutexes

47

(23)

3.2.1 Creating and destroying a mutex

49

(3)

3.2.2 Locking and unlocking a mutex

52

(9)

3.2.2.1 Nonblocking mutex locks

58

(3)

3.2.3 Using mutexes for atomicity

61

(1)

3.2.4 Sizing a mutex to fit the job

62

(1)

3.2.5 Using more than one mutex

63

(7)

3.2.5.1 Lock hierarchy

63

(7)

3.2.5.2 Lock chaining

70

(1)

3.3 Condition variables

70

(18)

3.3.1 Creating and destroying a condition variable

74

(3)

3.3.2 Waiting on a condition variable

77

(4)

3.3.3 Waking condition variable waiters

81

(1)

3.3.4 One final alarm program

82

(6)

3.4 Memory visibility between threads

88

(9)

4 A few ways to use threads

97

(34)

4.1 Pipeline

98

(8)

4.2 Work Crew

106

(14)

4.3 Client/Server

120

(11)

5 Advanced threaded programming

131

(66)

5.1 One-time initialization

131

(3)

5.2 Attributes objects

134

(8)

5.2.1 Mutex attributes

135

(2)

5.2.2 Condition variable attributes

137

(1)

5.2.3 Thread attributes

138

(4)

5.3 Cancellation

142

(19)

5.3.1 Deferred cancelability

147

(3)

5.3.2 Asynchronous cancelability

150

(4)

5.3.3 Cleaning up

154

(7)

5.4 Thread-specific data

161

(11)

5.4.1 Creating thread-specific data

163

(3)

5.4.2 Using thread-specific data

166

(1)

5.4.3 Using destructor functions

167

(5)

5.5 Realtime scheduling

172

(17)

5.5.1 POSIX realtime options

173

(1)

5.5.2 Scheduling policies and priorities

174

(7)

5.5.3 Contention scope and allocation domain

181

(2)

5.5.4 Problems with realtime scheduling

183

(2)

5.5.5 Priority-aware mutexes

185

(4)

5.5.5.1 Priority ceiling mutexes

186

(2)

5.5.5.2 Priority inheritance mutexes

188

(1)

5.6 Threads and kernel entities

189

(8)

5.6.1 Many-to-one (user level)

190

(1)

5.6.2 One-to-one (kernel level)

191

(2)

5.6.3 Many-to-few (two level)

193

(4)

6 POSIX adjusts to threads

197

(44)

6.1 fork

197

(7)

6.1.1 Fork handlers

199

(5)

6.2 exec

204

(1)

6.3 Process exit

204

(1)

6.4 Stdio

204

(5)

6.4.1 flockfile and funlockfile

205

(2)

6.4.2 getchar_unlocked and putchar_unlocked

207

(2)

6.5 Thread-safe functions

209

(5)

6.5.1 User and terminal identification

210

(2)

6.5.2 Directory searching

212

(1)

6.5.3 String token

212

(1)

6.5.4 Time representation

212

(1)

6.5.5 Random number generation

213

(1)

6.5.6 Group and user database

213

(1)

6.6 Signals

214

(27)

6.6.1 Signal actions

215

(1)

6.6.2 Signal masks

216

(1)

6.6.3 pthread_kill

217

(10)

6.6.4 sigwait and sigwaitinfo

227

(3)

6.6.5 SIGEV_THREAD

230

(4)

6.6.6 Semaphores: synchronizing with a signal-catching function

234

(7)

7 "Real code"

241

(48)

7.1 Extended synchronization

241

(29)

7.1.1 Barriers

242

(11)

7.1.2 Read-write locks

253

(17)

7.2 Work queue manager

270

(13)

7.3 But what about existing libraries?

283

(6)

7.3.1 Modifying libraries to be thread-safe

284

(1)

7.3.2 Living with legacy libraries

285

(4)

8 Hints to avoid debugging

289

(18)

8.1 Avoiding incorrect code

290

(12)

8.1.1 Avoid relying on "thread inertia"

291

(2)

8.1.2 Never bet your mortgage on a thread race

293

(4)

8.1.3 Cooperate to avoid deadlocks

297

(2)

8.1.4 Beware of priority inversion

299

(1)

8.1.5 Never share condition variables between predicates

300

(1)

8.1.6 Sharing stacks and related memory corrupters

301

(1)

8.2 Avoiding performance problems

302

(5)

8.2.1 Beware of concurrent serialization

302

(1)

8.2.2 Use the right number of mutexes

303

(1)

8.2.2.1 Too many mutexes will not help

304

(1)

8.2.3 Never fight over cache lines

304

(3)

9 POSIX threads mini-reference

307

(40)

9.1 POSIX 1003.1c-1995 options

307

(1)

9.2 POSIX 1003.1c-1995 limits

308

(1)

9.3 POSIX 1003.1c-1995 interfaces

309

(38)

9.3.1 Error detection and reporting

310

(1)

9.3.2 Use of void* type

311

(1)

9.3.3 Threads

311

(5)

9.3.4 Mutexes

316

(3)

9.3.5 Condition variables

319

(4)

9.3.6 Cancellation

323

(2)

9.3.7 Thread-specific data

325

(1)

9.3.8 Realtime scheduling

326

(10)

9.3.9 Fork handlers

336

(1)

9.3.10 Stdio

336

(2)

9.3.11 Thread-safe functions

338

(4)

9.3.12 Signals

342

(3)

9.3.13 Semaphores

345

(2)

10 Future standardization

347

(16)

10.1 X/Open XSH5 [UNIX98]

347

(9)

10.1.1 POSIX options for XSH5

348

(1)

10.1.2 Mutex type

349

(2)

10.1.3 Set concurrency level

351

(2)

10.1.4 Stack guard size

353

(1)

10.1.5 Parallel I/O

354

(1)

10.1.6 Cancellation points

355

(1)

10.2 POSIX 1003.1j

356

(5)

10.2.1 Barriers

358

(1)

10.2.2 Read-write locks

358

(1)

10.2.3 Spinlocks

359

(1)

10.2.4 Condition variable wait clock

359

(2)

10.2.5 Thread abort

361

(1)

10.3 POSIX 1003.14

361

(2)

Bibliography

363

(4)

Thread resources on the Internet

367

(2)

Index

369

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Programming with POSIX Threads

Summary

Author Biography

Table of Contents

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Programming with POSIX Threads

Summary

Author Biography

Table of Contents

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