Parallel SynchronizationModel in C

• Critical section and Barrier

#pragma omp parallel private(i,j)shared(a,b,m,n,sum)

for( j=1; j<=n; j++ ) {

#pragma omp for

for( i=1; i<=m; i++ ) {

#pragma omp critical

sum=sum+a(i,j);

}

#pragma omp barrier

b(j) = sum;

}

j =1

for

i=1

i=2

i=3

Parallel

j = 2

for

Mutual exclusion

as threads update sum

(Reduction and Atomic

also available)

Wait until all threads

have finished column

sum. (Barrier actually

built into end do.)

. . .

All threads

barrier

All threads take turns

updating shared sum

Previous slide

Next slide

Back to first slide

View graphic version