Process Synchronization

PROCESS SYNCHRONIZATION SONALI C. UDIT-SYBSc-IT 2008-09

INTRODUCTION ,[object Object],[object Object],[object Object]

CRITICAL SECTION ,[object Object],[object Object],[object Object],[object Object]

CRITICAL SECTION ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Cont… Entry section exit section GENERAL STRUCTURE OF A TYPICAL PROCESS Pi

CRITICAL SECTION ,[object Object],[object Object],[object Object],[object Object],Cont…

TWO-PROCESS SOLUTION ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

TWO-PROCESS SOLUTION -Algorithm 1 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Do{ Critical section remainder section }while(1) For Process P i while (turn != i); Turn = j;

TWO-PROCESS SOLUTION -Algorithm 2 ,[object Object],[object Object],[object Object],[object Object],do { flag[i] = true; // declare your own interest while (flag[ j]) ; //wait if the other guy is interested critical section flag [i] = false; // declare that you lost interest remainder section // allows other guy to enter } while (1);

[object Object],[object Object],[object Object],[object Object],TWO-PROCESS SOLUTION -Algorithm 2

[object Object],TWO-PROCESS SOLUTION -Algorithm 3 For Process P i do { flag [i] = true; // declare your interest to enter turn = j; // assume it is the other’s turn-give PJ a chance while (flag [ j ] and turn == j) ; critical section flag [i] = false; remainder section } while (1);

[object Object],[object Object],[object Object],TWO-PROCESS SOLUTION -Algorithm 3

MULTIPLE-PROCESS SOLUTIONS - Bakery Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],MULTIPLE-PROCESS SOLUTIONS - Bakery Algorithm

[object Object],MULTIPLE-PROCESS SOLUTIONS - Bakery Algorithm

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],do { /* Has four states: choosing, scanning, CS, remainder section */ critical section /* no longer a candidate for CS entry */ remainder section } while (1); number[i] = 0;

SEMAPHORSES ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

SEMAPHORSES ,[object Object],Definition-Wait wait(S) { while(S<=0) ; //no-op S--; } Definition-signal Signal(S) { S++; }

[object Object],struct semaphore { int count; queueType queue; } void wait(semaphore s) { s.count--; if (s.count < 0) { place this process in s.queue; block this process } } void signal(semaphore s) { s.count++; if (s.count <= 0) { remove a process P from s.queue; place process P on ready list; } }

SEMAPHORES -Two Type ,[object Object],[object Object],[object Object]

SEMAPHORES -Binary Semaphores ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Process Synchronization

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