如何保证动态分配的数组是私人的OpenMP [英] How to ensure a dynamically allocated array is private in openmp
问题描述
我用C使用OpenMP使用Linux机器上的gcc工作。在for循环OpenMP并行,我可以声明一个静态分配的数组为私有。考虑code片段:
I'm working in C with openMP using gcc on a linux machine. In an openmp parallel for loop, I can declare a statically allocated array as private. Consider the code fragment:
int a[10];
#pragma omp parallel for shared(none) firstprivate(a)
for(i=0;i<4;i++){
和一切正常。但是,如果不是我分配一个动态,
And everything works as expected. But if instead I allocate a dynamically,
int * a = (int *) malloc(10*sizeof(int));
#pragma omp parallel for shared(none) firstprivate(a)
的值的(至少一个[1 ... 9])没有被保护,但是充当如果它们共享。这是可以理解为没有在编译命令似乎告诉OMP的数组有多大是需要是私有的。我怎么能将此信息传递给OpenMP的?我如何申报了整个的动态分配的数组为私有?
the values of a (at least a[1...9]) are not protected but act as if they are shared. This is understandable as nothing in the pragma command seems to tell omp how big the array a is that needs to be private. How can I pass this information to openmp? How do I declare the entire the dynamically allocated array as private?
推荐答案
我不认为你做的 - 我做了什么来解决这个问题,使用并行区域的#pragma OMP PARALLEL共享(。 ..)民营(...)
和动态分配的并行区域内的阵列。试试这个:
I don't think you do - what I did to solve this problem was used a parallel region #pragma omp parallel shared(...) private(...)
and allocated the array dynamically inside the parallel region. Try this:
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
/* compile with gcc -o test2 -fopenmp test2.c */
int main(int argc, char** argv)
{
int i = 0;
int size = 20;
int* a = (int*) calloc(size, sizeof(int));
int* b = (int*) calloc(size, sizeof(int));
int* c;
for ( i = 0; i < size; i++ )
{
a[i] = i;
b[i] = size-i;
printf("[BEFORE] At %d: a=%d, b=%d\n", i, a[i], b[i]);
}
#pragma omp parallel shared(a,b) private(c,i)
{
c = (int*) calloc(3, sizeof(int));
#pragma omp for
for ( i = 0; i < size; i++ )
{
c[0] = 5*a[i];
c[1] = 2*b[i];
c[2] = -2*i;
a[i] = c[0]+c[1]+c[2];
c[0] = 4*a[i];
c[1] = -1*b[i];
c[2] = i;
b[i] = c[0]+c[1]+c[2];
}
free(c);
}
for ( i = 0; i < size; i++ )
{
printf("[AFTER] At %d: a=%d, b=%d\n", i, a[i], b[i]);
}
}
这对我产生了相同的结果,我先前的实验计划:
That to me produced the same results as my earlier experiment program:
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
/* compile with gcc -o test1 -fopenmp test1.c */
int main(int argc, char** argv)
{
int i = 0;
int size = 20;
int* a = (int*) calloc(size, sizeof(int));
int* b = (int*) calloc(size, sizeof(int));
for ( i = 0; i < size; i++ )
{
a[i] = i;
b[i] = size-i;
printf("[BEFORE] At %d: a=%d, b=%d\n", i, a[i], b[i]);
}
#pragma omp parallel for shared(a,b) private(i)
for ( i = 0; i < size; i++ )
{
a[i] = 5*a[i]+2*b[i]-2*i;
b[i] = 4*a[i]-b[i]+i;
}
for ( i = 0; i < size; i++ )
{
printf("[AFTER] At %d: a=%d, b=%d\n", i, a[i], b[i]);
}
}
在猜测我会说,因为OpenMP的不能推导出数组的大小就不能私有 - 只有编译时数组可以这样做。我得到段错误,当我尝试私人动态分配的数组,presumably因为访问违规。分配,如果你写这个的pthreads使用每个线程的阵列是有道理的,解决这个问题。
At a guess I'd say because OpenMP can't deduce the size of the array it can't be private - only compile-time arrays can be done this way. I get segfaults when I try to private a dynamically allocated array, presumably because of access violations. Allocating the array on each thread as if you'd written this using pthreads makes sense and solves the issue.
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