Difference between revisions of "OpenMP in Small Bites/Scoping"
OpenMP in Small Bites/Scoping
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{{hidden begin | {{hidden begin | ||
| − | |title = 2. What is the data scoping of the variables <code>a</code>, <code>b</code>, <code>c</code> and <code>d</code> in the following code snippet in the parallel region? What is printed when executing the code? | + | |title = 2. What is the data scoping of the variables <code>a</code>, <code>b</code>, <code>c</code> and <code>d</code> in the following code snippet in the parallel region? What is printed when executing the code? <br> |
| + | <code>int a = 0;<br /> int b = 23;<br /> int c = -3;<br /> # pragma omp parallel num_threads(2) private(a) reduction(+:c)<br /> { </code> <div style="margin-left: 1em;"><code>int d = omp_get_thread_num();<br /> a = 42 + d;<br /> # pragma omp critical<br /> b = 1;<br /> c += a + b;</code></div> <code>} <br />c = c / 2;<br /> printf("a=%d, b=%d, c=%d\n", a, b, c) </code><br /> | ||
}} | }} | ||
<quiz display=simple> | <quiz display=simple> | ||
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|type="()"} | |type="()"} | ||
+ Click and submit to see the answer | + Click and submit to see the answer | ||
| − | || | + | ||{{Note|'''a: shared, b: private, c: firstprivate (due to the reduction clause), d: private '''<br />'''output: <code>a:0, b:1, c:42</code>'''}} |
</quiz> | </quiz> | ||
{{hidden end}} | {{hidden end}} | ||
Revision as of 18:34, 2 November 2020
| HPC.NRW | |
|---|---|
 | |
| Other HPC Courses | |
| 1. | Gprof Tutorial |
| 2. | Introduction to Linux in HPC |
| OpenMP in Small Bites | |
| 1. | Overview |
| 2. | Worksharing |
| 3. | Data Scoping |
| 4. | Non-Uniform Memory Access
|
Video
Quiz
1. What is the default data scoping of variable in a parallel region when this variable is declared before a parallel region?
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)
3. The following code snippet is wrong due to a missing data sharing attribute. How can you fix it?