taskgroup | RookieHPC

Definition

The taskgroup construct specifies a wait on completion of child tasks of the current task and their descendent tasks. It contrasts with the taskwait construct which waits only on child tasks but not their descendents.

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#pragma omp taskgroup [clause[[,]clause]...] <new-line>
    <structured-block>

Parameters

clause [Optional]

The clause to appear on the taskgroup construct, which is one of the following:

task_reduction(identifier : list)
allocate([allocator :] list)

Example

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

/**
 * @brief Illustrates how to do use the taskgroup construct.
 * @details This example consists in calculating the sum of all elements of an
 * array.
 **/
int main(int argc, char* argv[])
{
    // Use 2 threads when creating OpenMP parallel regions
    omp_set_num_threads(2);

    int total = 0;
    const int ARRAY_SIZE = 10;
    int* myArray = malloc(sizeof(int) * ARRAY_SIZE);
    if(myArray == NULL)
    {
        printf("Cannot allocate the array \"myArray\".\n");
        return EXIT_FAILURE;
    }

    // Initialise the array
    for(int i = 0; i < ARRAY_SIZE; i++)
    {
        myArray[i] = i;
    }

    // Calculate the sum of all elements
    #pragma omp parallel
    {
        #pragma omp single
        {
            #pragma omp taskgroup task_reduction(+: total)
            {
                for(int i = 0; i < ARRAY_SIZE; i++)
                {
                    #pragma omp task in_reduction(+: total)
                    {
                        total += myArray[i];
                    }
                }
            }
        }
    }

    printf("The sum of all array elements is %d.\n", total);
    free(myArray);

    return EXIT_SUCCESS;
}