Registers Shared Memory Fail-crash, fail-silent BJRN A. JOHNSSON - - PowerPoint PPT Presentation

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Jul 16, 2023 268 likes •627 views

Registers Shared Memory Fail-crash, fail-silent BJRN A. JOHNSSON Introduction Analogy from multi-CPU computers. Over network: emulation of shared-memory . Benefit: use shared-memory where there really is none. Considered

SLIDE 1

Registers – Shared Memory

Fail-crash, fail-silent

BJÖRN A. JOHNSSON

SLIDE 2

Introduction

Analogy from multi-CPU computers.
Over network: emulation of shared-memory.
Benefit: use shared-memory where there really is none.
Considered easier than message exchanges.

SLIDE 3

Register Overview

Process starts read operation with ⟨ r, Read ⟩
Process starts write operation with ⟨ r, Write | v ⟩
Process completes after reply event from register:

– ⟨ r, ReadReturn | v ⟩ – ⟨ r, WriteReturn ⟩

Processes access registers in sequential manner
Types: (1, 1), (1, N), (N, N)

SLIDE 4

Semantics

Liveness: Every operation eventually completes.
Safety: Every read operation returns the value written by

the last write operation.

SLIDE 5

Concurrency

Serial (or sequential) exec: one operation after another
Concurrent exec: what happens to def. of “last”?
Three abstractions: safe, regular, and atomic.

SLIDE 6

Algorithm Overview

(1, N) Regular Register

– Read-One Write-All – Majority Voting Regular Register

(1, N) Atomic Register

– (1, N) Regular ➞ (1, 1) Atomic ➞ (1, N) Atomic Register – Read-Impose Write-All – Read-Impose Write-Majority

(N, N) Atomic Register

– (1, N) Atomic➞ (N, N) Atomic Register – Read-Impose Write-Consult-All – Read-Impose Write-Consult-Majority

SLIDE 7

Repetition

Distributed-System Models

Fail-stop

– crash-stop, perfekt links, perfect failure detector (P)

Fail-silent

– crash-stop, perfekt links, no failure detector

SLIDE 8

(1, N) Regular Register

!

initially ⊥

SLIDE 9

(1, N) Regular Register

“x” also regular

SLIDE 10

(1, N) Regular Register

Read-One Write-All

SLIDE 11

(1, N) Regular Register

Read-One Write-All

SLIDE 12

(1, N) Regular Register

Read-One Write-All

SLIDE 13

(1, N) Regular Register

Majority Voting Regular Register

SLIDE 14

(1, N) Regular Register

Majority Voting Regular Register

returns pair with greatest time stamp

SLIDE 15

(1, N) Atomic Register

!

SLIDE 16

(1, N) Atomic Register

SLIDE 17

(1, N) Atomic Register

SLIDE 18

(1, N) Atomic Register

(1, N) Regular ➞ (1, 1) Atomic Register

SLIDE 19

(1, N) Atomic Register

(1, 1) Atomic ➞ (1, N) Atomic Register

SLIDE 20

(1, N) Atomic Register

(1, 1) Atomic ➞ (1, N) Atomic Register

SLIDE 21

(1, N) Atomic Register

Read-Impose Write-All

same for ⟨ onar, Write ⟩ !

SLIDE 22

(1, N) Atomic Register

Read-Impose Write-All

same for ⟨ onar, Read ⟩ !

SLIDE 23

(1, N) Atomic Register

Read-Impose Write-Majority

SLIDE 24

(1, N) Atomic Register

Read-Impose Write-Majority

SLIDE 25

(1, N) Atomic Register

Read-Impose Write-Majority

SLIDE 26

(N, N) Atomic Register

!

SLIDE 27

(N, N) Atomic Register

SLIDE 28

(N, N) Atomic Register

(1, N) Atomic➞ (N, N) Atomic Register

SLIDE 29

(N, N) Atomic Register

(1, N) Atomic➞ (N, N) Atomic Register

SLIDE 30

(N, N) Atomic Register

Read-Impose Write-Consult-All

SLIDE 31

(N, N) Atomic Register

Read-Impose Write-Consult-All

SLIDE 32

(N, N) Atomic Register

Read-Impose Write-Consult-Majority

SLIDE 33

(N, N) Atomic Register

Read-Impose Write-Consult-Majority

factors in rank

SLIDE 34

(N, N) Atomic Register

Read-Impose Write-Consult-Majority

SLIDE 35