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Silberschatz, Galvin and Gagne 2007Operating System Concepts with Java 7thEdition, Nov 15, 2006

Chapter 6 (a): Synchronization

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6.2 Silberschatz, Galvin and Gagne 2007Operating System Concepts with Java 7thEdition, Nov 15, 2006

Module 6: Process Synchronization

Background Producer/Consumer Again Race Conditions Scheduler Assumptions The Critical-Section Problem

Critical Section Goals Deriving a Solution Petersons Algorithm Baker! Algorithm "ard#are Support

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6.3 Silberschatz, Galvin and Gagne 2007Operating System Concepts with Java 7thEdition, Nov 15, 2006

Background

Concurrent access to shared data ma! result in data

inconsistenc! $aintaining data consistenc! re%uires mechanisms to

ensure the orderl! e&ecution o' cooperatingprocesses

Suppose that #e #anted to provide a solution to theconsumer-producer problem that 'ills all the bu''ers( "ave an integer countthat tracks the number o' 'ull

bu''ers( )nitiall!* count is set to +( Producer increments count a'ter producing a bu''er Consumer decrements a'ter consuming a bu''er

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6.4 Silberschatz, Galvin and Gagne 2007Operating System Concepts with Java 7thEdition, Nov 15, 2006

Producer-Consumer

Producer

#hile ,true .

/ produce an item and /

/ put in ne&tProduced /

#hile ,count 00 B1223R4S)53

6 // do nothing b/c 'ull

bu''er 7in8 0 ne&tProduced6

in 0 ,in 9 : ; B1223R4S)536

count996

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6.5 Silberschatz, Galvin and Gagne 2007Operating System Concepts with Java 7thEdition, Nov 15, 2006

Race Condition

count99could be implemented as

register: 0 count register: 0 register: 9 : count 0 register:

count--could be implemented as

register= 0 count register= 0 register= - : count 0 register=

Consider this e&ecution interleaving #ith >count 0 ?@ initiall!

S+ producer e&ecute register: 0 count .register: 0 ?