Openmp thread control in C

Question

If I have a parallel section code, is it possible to assign a specific thread to each section, i.e. something of the sort

#pragma omp sections num_threads(2)
{
   #pragma omp section  //<---assigned to master thread
    {
      //do something
     }
    #pragma omp section  //<---assigned to the other thread
    {
      //do something
     }

}

Hristo Iliev · Accepted Answer · 2013-02-18 14:12:51Z

3

Assignment of OpenMP sections to threads is done in an implementation-dependent manner. The only directive that results in specific execution thread is master.

If you really need to give thread-specific work to each thread, use conditionals over the return value of omp_get_thread_num():

#pragma omp parallel num_threads(2)
{
   switch (omp_get_thread_num())
   {
      case 0:
         // Code for thread 0
         break;
      case 1:
         // Code for thread 1
         break;
      default:
         break;
   }
}

answered Feb 18, 2013 at 14:12

Hristo Iliev

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2 Comments

Brian Attwell Over a year ago

Does num_threads(2) guarantee that you will get thread 0 and 1, not thread 2 and 3?

Hristo Iliev Over a year ago

Threads in OpenMP parallel regions are always numbered starting from 0.

Aizen · Accepted Answer · 2013-02-18 05:50:48Z

0

For assigning to the master thread you can use

#pragma omp master

answered Feb 18, 2013 at 5:50

Aizen

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