reduction

各スレッドに対してプライベートである一つ以上の変数が並列領域の最後にあるリダクション演算の項目であることを指定します。

reduction(operation:var)

解説

指定項目

• operation
  並列領域のエッジにおける変数 ()var に対して実行する操作の演算子。

• var
  1 つスカラー縮小を実行する別の変数。複数の変数を指定する場合はコンマで区切ります。変数名。

解説

reduction は次のディレクティブに対象 :

• 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

関連項目

OpenMP 句