Private Malloc的OpenMP Seg Fault

當我嘗試在openmp for循環中移動一個malloc調用時，我遇到了Seg故障的一個有趣問題。每個線程都必須計算它自己的距離向量副本，以正確計算分類，因此向量必須是私有的......但是，當我嘗試使用多於1個線程調用它時，它會導致seg錯誤。如果將p_distances向量聲明爲共享，則不會發生這種情況，儘管這會導致線程相互覆蓋，從而導致距離計算不準確。是否存在一些非常明顯的規則，我在這裏違反了...另外，我知道在我的代碼中還有其他不好的代碼實踐。我總是樂於提出有關風格的建議，但請幫助我關注實際導致問題的原因。Private Malloc的OpenMP Seg Fault

int *labels_train; 
float *data_train; 
int *labels_test; 
float *data_test; 
float *s_distances; 
int *s_results, *p_results; 
int i, j, k, h; 
int N, D, K, M, thread_count; 

void sort(float *_distances, int *_labels_train, int _N); 

void computeParallelKNN() 
{ 
// this is the target loop for multi-point parallelization 
// seg fault here whenever p_distances malloc is moved inside parallel for loop and declared private 
#pragma omp parallel for num_threads(thread_count) private(h, j, i) 
for (i = 0; i < M; i++) 
{ 
    float *p_distances = (float*)malloc(N * sizeof(float)); 
    k = 0; 

    // This is the target loop for single point parallelization 
    // No dependencies on outer loop (each thread can calculate distance for current point with some 
    // different training point) 
    for (h = 0; h < N*D; h+=D) 
    { 
     float dTmp = 0; 
     // Reduction operation..no dependencies here either (I don't think?) 
     // dTmp is critical variable for parallel operations 
     for (j = 0; j < D; j++) 
     { 
      dTmp += pow(data_test[i*D+j] - data_train[h+j],2); 
     } 
     p_distances[k] = (float)sqrt((double)dTmp); 
     k++; 
    } 

    // Make a copy of labels (since sort will invalidate original data/labels correlation) 
    int *temp_labels; 
    temp_labels = (int*)malloc(N * sizeof(int)); 
    for (h = 0; h < N; h++) 
     temp_labels[h] = labels_train[h]; 

    // Sort distances/labels_train vector 
    sort(p_distances, temp_labels, N); 

    // Calculate/print KNN classification 
    int neg = 0; 
    int pos = 0; 
    for (h = 0; h < K; h++) 
    { 
     if(temp_labels[h] == -1) neg++; 
     else pos++; 
    } 
    if (pos > neg) p_results[i] = 1; 
    else p_results[i] = -1; 

    free(p_distances); 
     } 
} 

// Selection sort algorithm modified to sort labels according to distance data 
void sort(float *_distances, int *_labels_train, int _N) 
{ 
    int k; 
    for (k = 1; k < _N; ++k) 
    { 
    float dist_key = _distances[k]; 
    int label_key = _labels_train[k]; 
    int i = k - 1; 
    while ((i >= 0) && (dist_key < _distances[i])) 
    { 
     _distances[i + 1] = _distances[i]; 
     _labels_train[i + 1] = _labels_train[i]; 
     --i; 
    } 
    _distances[i + 1] = dist_key; 
    _labels_train[i + 1] = label_key; 
}

}

我可以張貼的完整代碼，但是這絕對是在故障發生的區域。在此先感謝，希望這只是我犯的一個愚蠢的錯誤。

來源

2011-12-06 NAW

我不是100％肯定，爲什麼你的代碼不能正常工作。但是你是否嘗試過在循環外聲明p_distance，並按照以下方式爲每個線程分配它：'#pragma omp parallel private（p_distance，i，j，k etc。）\ n {p_distance = calloc（N，sizeof（float ））; \ n #pragma omp for \ n {for（i = 0; i Bort

首先，有k這是跨所有線程共享;沒有任何聲明通知它周圍的關鍵部分或者應該以原子方式進行。

以更清晰的方式重寫您的代碼並儘可能避免使用全局變量 - 您可以在剛進入新範圍時定義變量。

例如，

int i; 
void foo() { 
#pragma parallel private(i) 
{ 
    // ... 
}

是一樣的：

void foo() { 
#pragma parallel 
{ 
    int i; 
    // ... 
}

來源

2011-12-07 17:55:22 ipapadop

Private Malloc的OpenMP Seg Fault

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