Difference between revisions of "OpenMP in Small Bites/Tasking and Data Scoping"

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OpenMP in Small Bites/Tasking and Data Scoping
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<code>#pragma omp parallel num_threads(4)</code><br/>
 
<code>#pragma omp parallel num_threads(4)</code><br/>
 
<code>{</code><br/>
 
<code>{</code><br/>
−
<code>  #pragma omp task</code><br/>
+
<div style="margin-left: 1em;"><code>  #pragma omp task</code></div>
−
<code>  {</code><br/>
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<div style="margin-left: 1em;"><code>  {</code></div>
−
<code>    y += x;</code><br/>
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<div style="margin-left: 2em;"><code>    y += x;</code></div>
−
<code>  }</code><br/>
+
<div style="margin-left: 1em;"><code>  }</code></div>
 
<code>}</code><br/>
 
<code>}</code><br/>
 
<code>printf("y=%d\n", y);</code><br/>
 
<code>printf("y=%d\n", y);</code><br/>
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<code>#pragma omp parallel num_threads(4)</code><br/>
 
<code>#pragma omp parallel num_threads(4)</code><br/>
 
<code>{</code><br/>
 
<code>{</code><br/>
−
<code>  #pragma omp single</code><br/>
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<div style="margin-left: 1em;"><code>  #pragma omp single</code></div>
−
<code>  {</code><br/>
+
<div style="margin-left: 1em;"><code>  {</code></div>
−
<code>    #pragma omp task</code><br/>
+
<div style="margin-left: 2em;"><code>    #pragma omp task</code></div>
−
<code>    {</code><br/>
+
<div style="margin-left: 2em;"><code>    {</code></div>
−
<code>      y += x;</code><br/>
+
<div style="margin-left: 3em;"><code>      y += x;</code></div>
−
<code>    }</code><br/>
+
<div style="margin-left: 2em;"><code>    }</code></div>
−
<code>  }</code><br/>
+
<div style="margin-left: 1em;"><code>  }</code></div>
 
<code>}</code><br/>
 
<code>}</code><br/>
 
<code>printf("y=%d\n", y);</code><br/>
 
<code>printf("y=%d\n", y);</code><br/>

Revision as of 18:05, 30 November 2020

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
9. Tasking Example: Sudoku Solver
10. Task Scheduling
11. Non-Uniform Memory Access

Video

Quiz

1. Consider the following code snippet

int x = 42;
#pragma omp parallel private(x)
{

#pragma omp task
{
x = 3;
}

}
printf("x=%d\n", x);

What is the data scope of x and what is printed?

firstprivate, x=42
firstprivate, x=3
shared, x=3

2. Consider the following code snippet

int x = 42;
int y = 0;
#pragma omp parallel num_threads(4)
{

#pragma omp task
{
y += x;
}

}
printf("y=%d\n", y);

What is the data scope of x and what is printed?

shared, y=42
shared, y=168
firstprivate, y=168

3. Consider the following code snippet

int x = 42;
int y = 0;
#pragma omp parallel num_threads(4)
{

#pragma omp single
{
#pragma omp task
{
y += x;
}
}

}
printf("y=%d\n", y);

What is the data scope of x and what is printed?

shared, y=42
shared, y=168
firstprivate, y=168

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