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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <style type="text/css"> body { font-family: Verdana, Arial, Helvetica, sans-serif;} a.at-term { font-style: italic; } </style> <title>Problems specific to OpenMP</title> <meta name="Generator" content="ATutor"> <meta name="Keywords" content=""></head><body> <h3>OMP_NUM_THREADS environment variable not initialized</h3>
<p>Most systems have a default value for OMP_NUM_THREADS, which controls the number of OpenMP threads for the program. This value will vary from system to system, so it is important to explicitly define this environment variable in all batch jobs. The following ksh example causes a.out to use 5 processors if they are available: </p>
<pre><code>export OMP_NUM_THREADS=5
a.out</code></pre>
<p>The omp_get_num_threads function can be called within a program to determine the number of threads assigned to that program.</p>
<pre><code> integer function omp_get_num_threads
int omp_get_num_threads();</code></pre>
<p>Alternatively, the number of threads can be controlled from within the code with a call to the OMP_SET_NUM_threads routine. </p>
<pre><code> int nthrds
nthreads=5
call omp_set_num_threads(nthrds)</code></pre>
<h3>Common syntax errors</h3>
<p>These errors will usually result in compiletime errors. The most common error for programmers new to OpenMP is implementing an OpenMP function as a subroutine call or vice versa.</p>
<h3>Loop variables not declared correctly (shared or private)</h3>
<p>These errors will result in runtime errors or cause the code to crash. Generally, not declaring variables private/shared correctly will cause data to become corrupted.</p></body></html>⌨️ 快捷键说明
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