### News

- 2019-07-09: we are online!

### Schedule

Type | Day | Time | Hall | Start | Lecturer |
---|---|---|---|---|---|

Lecture | Mon | 14:30 – 16:00 | AH 1 | 07 Oct | Katoen/Noll |

Tue | 14:30 – 16:00 | AH 1 | 08 Oct | Katoen/Noll | |

Exercise | Thu | 14:30 – 16:00 | 5056 | 17 Oct | Batz/Matheja |

### Contents

Today, *concurrent programming* has become mainstream, dictated by need for ever increasing performance which, having reached the end of Moore’s law, can only be achieved by parallelism. Indeed, application software from areas such as medicine or natural sciences heavily relies on parallel hardware infrastructure like (GP)GPU accelerators, FPGAs, and multi- and many-core machines. However, it is also today that we see *concurrency faults* coming up every day. The simple reason is that writing concurrent programs is difficult. Most programmers “think sequentially” and therefore make mistakes when writing concurrent software. Notorious programming errors include deadlock and violations of atomicity or order of operations, which are mainly caused by the wrong use of synchronization primitives like semaphores or locks. Even worse, the inherent non-deterministic behavior of concurrent software makes bugs difficult to reproduce. Addressing these challenges requires efforts from multiple related disciplines, involving concurrency bug detection, program testing and validation, and programming language design.

Another important area of computer science where concurrency naturally arises is that of *reactive systems*, which maintain an ongoing interaction with their environment. In contrast to sequential systems whose meaning is defined by the results of *finite computations*, the behavior of reactive systems is mainly determined by concurrent execution, communication, interaction, and mobility of *non-terminating processes*. Typical examples include operating systems, control systems for production lines, power plants, or vehicles. As many of such systems are safety critical, their development calls for rigorous formal techniques for design, implementation, and validation.

The aim of this course is to provide a basic understanding of modeling formalisms for concurrent systems. It will address two basic approaches, which are respectively called the *interleaving* and the *true concurrency* approach. The former is based on the idea to reduce the phenomenon of concurrency to well-known concepts, by interpreting parallel behavior as non-deterministic merging of sequential execution. It is represented by various *process algebras*, which provide a formal apparatus for reasoning about structure and behaviour of systems in a compositional way. The true concurrency approach mainly comes in the form of *Petri nets*, which are well suited for explicitly modeling the concurrent behavior of distributed systems.

### Prerequisites

Basic knowledge of the following relevant undergraduate courses is expected:

- Programming (essential concepts of imperative and object-oriented programming languages and elementary programming techniques)
- Essential concepts of operating systems
- Formal Languages and Automata Theory (regular and context-free languages, finite and pushdown automata)
- Mathematical Logic

### Lectures

No. | Date | Lecturer | Topic | Slides |
---|---|---|---|---|

01 | 07 Oct | Noll | Introduction | l01 |

02 | 08 Oct | Noll | Calculus of Communicating Systems (CCS) | l02 |

03 | 14 Oct | Noll | Hennessy-Milner Logic | l03 |

04 | 15 Oct | Noll | Hennessy-Milner Logic with Recursion | l04 |

05 | 21 Oct | Noll | Fixed-Point Theory | l05 |

06 | 22 Oct | Noll | Mutually Recursive Equational Systems | l06 |

07 | 28 Oct | Noll | Modelling and Analysing Mutual Exclusion Algorithms & Value-Passing CCS | l07 |

08 | 29 Oct | Noll | The π-Calculus | l08 |

09 | 5 Nov | Noll | Example Reactions in π-Calculus | l09 |

10 | 11 Nov | Noll | Variations of π-Calculus | l10 |

11 | 12 Nov | Noll | Trace Equivalence | l11 |

12 | 18 Nov | Noll | Strong Bisimulation | l12 |

13 | 19 Nov | Noll | Properties of Strong Bisimulation | l13 |

14 | 25 Nov | Noll | Bisimulation as a Fixed Point and Weak Variants | l14 |

15 | 26 Nov | Noll | Hennessy-Milner Logic and Bisimilarity | l15 |

16 | 02 Dec | Katoen | Interleaving Semantics of Petri Nets | l16 |

17 | 09 Dec | Katoen | True Concurrency Semantics of Petri Nets (1) | l17 |

18 | 10 Dec | Katoen | True Concurrency Semantics of Petri Nets (2) | l18+l19 |

19 | 16 Dec | Katoen | McMillan Prefixes | |

20 | 17 Dec | Katoen | Petri Net Semantics of CCS |

### Exercises

No. | Due Date | Topic | Exercise |

01 | 17.10.2019 | CCS | e01 |

02 | 21.10.2019 | HML | e02 |

03 | 31.10.2019 | FP+HML | e03 |

04 | 07.11.2019 | HML+CCS+PiC | e04 |

05 | 14.11.2019 | CAAL+PiC | e05 |

06 | 21.11.2019 | Trace Equivalence | e06 |

07 | 28.11.2019 | Strong Bisimulation | e07 |

08 | 05.12.2019 | Weak Bisimulation | e08 |

09 | 12.12.2019 | Petri Nets | e09 |

10 | – | Old exams | ex1 / ex2 |

### Exam

- The form of the exam (written or oral) will be announced later.
- Registration is possible via RWTHonline; there are no specific requirements for admission.

### Evaluation results

### Further information

- The lectures will be given in German or English, depending on the language proficiency of the audience.
- The slides and other course material will be in
**English**. There are no lecture notes (yet); the course material will consist of slides.

### Background Literature

- Luca Aceto, Anna Ingólfsdóttir, Kim Guldstrand Larsen and Jiri Srba:
*Reactive Systems: Modelling, Specification and Verification*. Cambridge University Press, 2007. - Wolfgang Reisig:
*Understanding Petri Nets: Modeling Techniques, Analysis Methods, Case Studies*. Springer Verlag, 2012. - Maurice Herlihy and Nir Shavit:
*The Art of Multiprocessor Programming*. Elsevier, 2008. - Jan Bergstra, Alban Ponse and Scott Smolka (Eds.):
*Handbook of Process Algebra*. Elsevier, 2001.