Data copying

C | Fortran-90

copyin

Definition

copyin is a clause that can be used in a parallel construct; it acts as a mechanism to broadcast the value of a threadprivate variable from the master thread to the threadprivate variable of every other thread in the team executing the parallel region.

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copyin(list)

Parameters

list

The variables to pass as copyin, separated by commas.

Example

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#include <stdio.h>
#include <stdlib.h>
#include <omp.h>

int a = 12345;
#pragma omp threadprivate(a)

/**
 * @brief Illustrates how to use the copyin clause.
 * @details This application declares a global variable and specifies it as
 * threadprivate. This variable is then passed a copyin to the first parallel
 * region. In that region, the master thread modifies its value but other
 * threads will not see the update until the second parallel region; where the
 * variable will be passed as copyin again.
 **/
int main(int argc, char* argv[])
{
    // Turn off dynamic threads as required by threadprivate
    omp_set_dynamic(0);

    #pragma omp parallel copyin(a)
    {
        #pragma omp master
        {
            printf("[First parallel region] Master thread changes the value of a to 67890.\n");
            a = 67890;
        }

        #pragma omp barrier

        printf("[First parallel region] Thread %d: a = %d.\n", omp_get_thread_num(), a);
    }

    #pragma omp parallel copyin(a)
    {
        printf("[Second parallel region] Thread %d: a = %d.\n", omp_get_thread_num(), a);
    }

    return EXIT_SUCCESS;
}