1. Chair of Software Engineering Concurrent Object-Oriented Programming Prof. Dr. Bertrand Meyer Exercise Session 2: Introduction

2. 2 Overview Prisoners: Synchronization Safety vs. Liveness Amdahl’s Law

3. 3 Prisoners: Synchronization I will do nothing. toggle the light switch. announce that all prisoners have been interrogated.

4. 4 Prisoners: Synchronization Each prisoner will be interrogated arbitrarily often. More precisely, for any n, eventually each of the prisoners will be interrogated at least n times. If the announcement is true then all of the prisoners will be set free. Otherwise all of them will be executed. What is a winning strategy?

5. 5 Safety vs. Liveness safety: Nothing bad happens ever. liveness: Something good happens eventually. example  If two or more processes are waiting to enter their critical sections, at least one succeeds.  Is this a safety or a liveness property?  What is the good / bad thing?

6. 6 Amdahl’s Law parallel fraction sequential fraction number of processors