Data Scoping (OpenMP)

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OpenMP in Small Bites/Scoping
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Tutorial
Title: OpenMP in Small Bites
Provider: HPC.NRW

Contact: tutorials@hpc.nrw
Type: Multi-part video
Topic Area: Programming Paradigms
License: CC-BY-SA
Syllabus

1. Overview
2. Worksharing
3. Data Scoping
4. False Sharing
5. Tasking
6. Tasking and Data Scoping
7. Tasking and Synchronization
8. Loops and Tasks
10. Task Scheduling
11. Non-Uniform Memory Access

Contents

This video provides an overview on managing one of the most challenging parts of OpenMP: Data Scoping. It discusses the differences between private, firstprivate, lastprivate and shared variables and shows how to implement a scalable reduction.

Video

( Slides as pdf)

Quiz

1. What is the default data scoping of variable in a parallel region when this variable is declared before a parallel region?

Click and submit to see the answer

2. What is the data scoping of the variables a, b, c and d in the following code snippet in the parallel region? What is printed when executing the code?
int a = 0;
int b = 23;
int c = -3;
# pragma omp parallel num_threads(2) private(a) reduction(+:c)
{
int d = omp_get_thread_num();
a = 42 + d;
# pragma omp critical
b = 1;
c += a + b;
}
c = c / 2;
printf("a=%d, b=%d, c=%d\n", a, b, c)

Click and submit to see the answer

3. The following code snippet is wrong due to a missing data sharing attribute. How can you fix it?
int i, int s = 0;
# pragma omp parallel for
for (i = 1; i < 100; i++){
s = s + a[i];
}

Click and submit to see the answer