| title | 4.2 OMP_NUM_THREADS | Microsoft Docs | |||||||||||||
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| ms.date | 11/04/2016 | |||||||||||||
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| ms.topic | article | |||||||||||||
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| ms.assetid | 49dd55dd-25d5-4a5a-a998-cc7f47b2dae2 | |||||||||||||
| caps.latest.revision | 6 | |||||||||||||
| author | mikeblome | |||||||||||||
| ms.author | mblome | |||||||||||||
| manager | ghogen | |||||||||||||
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The OMP_NUM_THREADS environment variable sets the default number of threads to use during execution, unless that number is explicitly changed by calling the omp_set_num_threads library routine or by an explicit num_threads clause on a parallel directive.
The value of the OMP_NUM_THREADS environment variable must be a positive integer. Its effect depends upon whether dynamic adjustment of the number of threads is enabled. For a comprehensive set of rules about the interaction between the OMP_NUM_THREADS environment variable and dynamic adjustment of threads, see Section 2.3 on page 8.
If no value is specified for the OMP_NUM_THREADS environment variable, or if the value specified is not a positive integer, or if the value is greater than the maximum number of threads the system can support, the number of threads to use is implementation-defined.
Example:
setenv OMP_NUM_THREADS 16
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num_threads clause, see Section 2.3 on page 8.
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omp_set_num_threads function, see Section 3.1.1 on page 36.
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omp_set_dynamic function, see Section 3.1.7 on page 39.