reduction

各スレッドにプライベートな 1 つ以上の変数が、並行領域の最後にあるリダクション演算の対象であることを示します。

reduction(operation:var)

解説

指定項目

• operation
  並行領域の最後で変数 (var) に対して実行される演算の演算子。

• var
  スカラー リダクションを実行する対象の 1 つ以上の変数。 複数の変数を指定する場合、変数名の間をコンマで区切ります。

解説

reduction は次のディレクティブに適用されます。

• for (OpenMP)

• parallel

• sections (OpenMP)

詳細については、「2.7.2.6 reduction」を参照してください。

使用例

// omp_reduction.cpp
// compile with: /openmp
#include <stdio.h>
#include <omp.h>

#define NUM_THREADS 4
#define SUM_START   1
#define SUM_END     10
#define FUNC_RETS   {1, 1, 1, 1, 1}

int bRets[5] = FUNC_RETS;
int nSumCalc = ((SUM_START + SUM_END) * (SUM_END - SUM_START + 1)) / 2;

int func1( ) {return bRets[0];}
int func2( ) {return bRets[1];}
int func3( ) {return bRets[2];}
int func4( ) {return bRets[3];}
int func5( ) {return bRets[4];}

int main( ) 
{
    int nRet = 0, 
        nCount = 0, 
        nSum = 0, 
        i, 
        bSucceed = 1;

    omp_set_num_threads(NUM_THREADS);

    #pragma omp parallel reduction(+ : nCount)
    {
        nCount += 1;

        #pragma omp for reduction(+ : nSum)
        for (i = SUM_START ; i <= SUM_END ; ++i)
            nSum += i;

        #pragma omp sections reduction(&& : bSucceed)
        {
            #pragma omp section
            {
                bSucceed = bSucceed && func1( );
            }  

            #pragma omp section
            {
                bSucceed = bSucceed && func2( );
            }

            #pragma omp section
            {
                bSucceed = bSucceed && func3( );
            }

            #pragma omp section
            {
                bSucceed = bSucceed && func4( );
            }

            #pragma omp section
            {
                bSucceed = bSucceed && func5( );
            }
        }
    }

    printf_s("The parallel section was executed %d times "
             "in parallel.\n", nCount);
    printf_s("The sum of the consecutive integers from "
             "%d to %d, is %d\n", 1, 10, nSum);

    if (bSucceed)
        printf_s("All of the the functions, func1 through "
                 "func5 succeeded!\n");
    else
        printf_s("One or more of the the functions, func1 "
                 "through func5 failed!\n");

    if (nCount != NUM_THREADS) 
    {
        printf_s("ERROR: For %d threads, %d were counted!\n", 
                 NUM_THREADS, nCount);
        nRet |= 0x1;
   }

    if (nSum != nSumCalc) 
    {
        printf_s("ERROR: The sum of %d through %d should be %d, "
                "but %d was reported!\n", 
                SUM_START, SUM_END, nSumCalc, nSum);
        nRet |= 0x10;
    }

    if (bSucceed != (bRets[0] && bRets[1] && 
                     bRets[2] && bRets[3] && bRets[4])) 
    {
        printf_s("ERROR: The sum of %d through %d should be %d, "
                 "but %d was reported!\n", 
                 SUM_START, SUM_END, nSumCalc, nSum);
        nRet |= 0x100;
    }
}

参照

参照

OpenMP 句