Leslie Lamport. April 20, Leslie Lamport. Jenny Tyrväinen. Introduction. Education and Career. Most important works.

Transcription

1 April 20, 2016

2 Born February in New York

3 Mathematician by his education Has worked in industry, not an academic Fields: concurrency and distributed systems Lists 180 publications and other texts at his home page Several awards and honors (IEEE John von Neumann Medal 2008)

4 BSc at MIT 1960 MSc at Brandeis University 1963 Mitre Corporation Marlboro College Massachusetts Computer Associates (Compass)

5 continues PhD at Brandeis University 1972: The Analytic Cauchy with Singular Data SRI International Digital Equipment Corporation / Compaq Microsoft Research

6 , 1974 (Mutual exclusion) Works as queue ticket dispencers at bakery etc. Each process chooses own queue number by asking around and choosing a larger number If same number, process number decides Enters critical section on turn, smallest number first

7 Solves mutual exclusion problem! Doesn t rely on lower level Process can read all memory, write only its own: simultaneous read and write ok Process can read arbitrary value

8 , 1978 The Maintenance of Duplicate Databases by Paul Johnson and Bob Thomas Ordering of events: Two observers can disagree, which event happened first Synchronization of logical clocks to achieve partial ordering Expand to total ordering state-machine for arbitrary distributed system PODC Influential Paper Award 2000 and ACM SIGOPS Hall of Fame Award 2007

9 Clock conditions: C1. If a and b events in P i, and a comes before b, C i (a) < C i (b) C2. If a: P i sends a message and b is P j receiving it, C i (a) < C j (b) Implementation rules: IR1. Each process increments its clock between two successive events IR2. (a) event a: send m by process then include timestamp with current clock value (b) event b: receive m: process sets clock greater or equal to present value and greater than received timestamp

10 The, 1982 (consensus) SIFT: Design and Analysis of a Fault-Tolerant Computer for Aircraft Control, 1978 (Jean-Claude Laprie Award in Dependable Computing 2014) Reaching Agreement in the Presence of Faults, 1980 (Edsger W. Dijkstra Prize 2005) New paper mainly to assign a new name to the problem Jean-Claude Laprie Award in Dependable Computing 2013

11 The Group of generals deciding on attack/retreat, need to reach consensus Some are traitors, trying to get loyal generals to adopt a bad plan How many generals are needed to tolerate n traitors?

12 The Solution Solution with oral messages: 3n+1 generals With signatures: 2n+1 generals

13 OM(0): (1) Commander sends value to every lieutenant (2) Each lieutenant: use the value received or RETREAT, if no value OM(m), m > 0: if no value received, use RETREAT (1) Commander sends value to every lieutenant (2) every lieutenant uses OM(m-1) to send received value to n-2 other lieutenants (3) from received values, select majority

14 : Determining Global States of a Distributed System, 1985 Observer process: save state, send a token to all others Process on receiving token: save state, send to observer send token on every subsequent message If a process receives a message without the token, forward to observer The observer builds the global state ACM SIGOPS Hall of Fame Award 2013 and Edsger W. Dijkstra Prize in Distributed Computing 2014

15 L A TEX: A Document Preparation System, 1986 Macro package to Donald Knuth s TEX For writing the Great American Concurrency book (didn t) A user manual, published by Addison-Wesley

16 (TLA), 1994 Formalism for describing concurrent systems If you re not writing a program, don t use a programming language Developed also TLA+ and PlusCal TLA IDE Logic, algorithm language and tools for mechanically checking proofs

17 TLA Example IDE screenshot.png

18 The Part-Time Parliament, 1998 Tried to prove, that it is impossible to maintain consistency despite any number of non-byzantine faults Paxos algorithm instead Tried to popularize like the Byzantine generals problem ACM SIGOPS Hall of Fame Award 2012

19 Paxos algorithm The consensus algorithm: synod Three-phase: first value proposed, then accepted and lastly learned Client-server model, server duplicated: described as deterministic state-machine Fault-tolerance against arbitrary faults

20 Enormous impact on the development of distributed systems Developed many methods and concepts now considered elemental Mathematics to computer science: Formal descriptions Proofs for concurrency IEEE John von Neumann medal: For establishment of the foundations of distributed and concurrent computing

21 Thank you! Questions?