Mordechai (Moti) Ben-Ari is an Associate Professor in the Department of Science Teaching at the Weizmann Institute of Science in Rehovot, Israel. He is the author of texts on Ada, concurrent programming, programming languages, and mathematical logic, as well as Just a Theory: Exploring the Nature of Science. In 2004 he was honored with the ACM/SIGCSE Award for Outstanding Contribution to Computer Science Education.

Contents

Preface xi

1 What is Concurrent Programming? 1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Concurrency as abstract parallelism . . . . . . . . . . . . . . . . 2

1.3 Multitasking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 The terminology of concurrency . . . . . . . . . . . . . . . . . 4

1.5 Multiple computers . . . . . . . . . . . . . . . . . . . . . . . . 5

1.6 The challenge of concurrent programming . . . . . . . . . . . . 5

2 The Concurrent Programming Abstraction 7

2.1 The role of abstraction . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Concurrent execution as interleaving of atomic statements . . . . 8

2.3 Justification of the abstraction . . . . . . . . . . . . . . . . . . . 13

2.4 Arbitrary interleaving . . . . . . . . . . . . . . . . . . . . . . . 17

2.5 Atomic statements . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.6 Correctness . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.7 Fairness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.8 Machine-code instructions . . . . . . . . . . . . . . . . . . . . . 24

2.9 Volatile and non-atomic variables . . . . . . . . . . . . . . . . . 28

2.10 The BACI concurrency simulator . . . . . . . . . . . . . . . . . 29

2.11 Concurrency in Ada . . . . . . . . . . . . . . . . . . . . . . . . 31

2.12 Concurrency in Java . . . . . . . . . . . . . . . . . . . . . . . . 34

2.13 Writing concurrent programs in Promela . . . . . . . . . . . . . 36

2.14 Supplement: the state diagram for the frog puzzle . . . . . . . . 37

3 The Critical Section Problem 45

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.2 The definition of the problem . . . . . . . . . . . . . . . . . . . 45

3.3 First attempt . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.4 Proving correctness with state diagrams . . . . . . . . . . . . . . 49

3.5 Correctness of the first attempt . . . . . . . . . . . . . . . . . . 53

3.6 Second attempt . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

3.7 Third attempt . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

3.8 Fourth attempt . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3.9 Dekker’s algorithm . . . . . . . . . . . . . . . . . . . . . . . . 60

3.10 Complex atomic statements . . . . . . . . . . . . . . . . . . . . 61

4 Verification of Concurrent Programs 67

4.1 Logical specification of correctness properties . . . . . . . . . . 68

4.2 Inductive proofs of invariants . . . . . . . . . . . . . . . . . . . 69

4.3 Basic concepts of temporal logic . . . . . . . . . . . . . . . . . 72

4.4 Advanced concepts of temporal logic . . . . . . . . . . . . . . . 75

4.5 A deductive proof of Dekker’s algorithm . . . . . . . . . . . . . 79

4.6 Model checking . . . . . . . . . . . . . . . . . . . . . . . . . . 83

4.7 Spin and the Promela modeling language . . . . . . . . . . . . . 83

4.8 Correctness specifications in Spin . . . . . . . . . . . . . . . . . 86

4.9 Choosing a verification technique . . . . . . . . . . . . . . . . . 88

5 Advanced Algorithms for the Critical Section Problem 93

5.1 The bakery algorithm . . . . . . . . . . . . . . . . . . . . . . . 93

5.2 The bakery algorithm for N processes . . . . . . . . . . . . . . 95

5.3 Less restrictive models of concurrency . . . . . . . . . . . . . . 96

5.4 Fast algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

5.5 Implementations in Promela . . . . . . . . . . . . . . . . . . . . 104