Teacher: Chun-Yuan Lin

Introduction to Distributed AlgorithmPart Two: Fundamental AlgorithmChapter 8- Termination Detection Teacher: Chun-Yuan Lin Termination Detection

Termination Detection (1) • A computation of a distributed algorithm terminates when the algorithm has reached a terminal configuration. • The termination of the computation is said to be implicit. Termination is said to be explicitin a process if the state of that process in the terminal configuration is a terminal state of the process. • Implicit termination of the computation is also called message termination. Explicit termination is also called process termination. Termination Detection

Termination Detection (2) • In this chapter general methods will be investigated for transforming message-terminating algorithms into process-terminating ones. • The most difficult part of the transformation turns out to be the algorithm that detects the termination. • Termination detection is possible for all classes of networks for which a wave algorithm can be given. Termination Detection

Definitions (1) Termination Detection

Definitions (2) • Some assumptions are made in order to simplify the description of the algorithms in this chapter. • An active process becomes passive only in an internal event. • A process always becomes active when a message is received. • The internal events in which p becomes passive are the only internal events of p. Termination Detection

Two Lower Bounds Termination Detection

Terminating the Processes (1) Termination Detection

Terminating the Processes (2) Termination Detection

Computation Trees and Forests (1) • Termination is detected when the computation graph becomes empty. (network is undirected) • The Dijkstra-Scholten Algorithm (Tree) Termination Detection

Computation Trees and Forests (2) Termination Detection

Computation Trees and Forests (3) • The Shavit-Francez Algorithm (Forests) Termination Detection

Wave-based Solutions (1) • We shall first consider concrete instances of the algorithms, where in all cases the wave algorithm is the ring algorithm. • The Dijkstra-Feijen- Van Gasteren Algorithm Termination Detection

Wave-based Solutions (2) Termination Detection

Wave-based Solutions (5) • Counting Basic Messages: Safra's Algorithm Termination Detection

Wave-based Solutions (8) • Using Acknowledgements Termination Detection

Wave-based Solutions (11) • Termination Detection with Waves Termination Detection

Other Solutions (1) • The Credit-recovery Algorithm Termination Detection

Other Solutions (2) Termination Detection

Other Solutions (4) • Solutions Using Timestamps Termination Detection

Teacher: Chun-Yuan Lin