c - openmp是否分配内存并释放所有内存

Question

openmp 是否分配内存并释放所有内存？因为我运行了 valgrind，并释放了我所有的列表。我 malloc 的所有东西，我都释放了。

==11442== HEAP SUMMARY:
==11442==     in use at exit: 192 bytes in 1 blocks
==11442==   total heap usage: 2,001 allocs, 2,000 frees, 2,917,280 bytes allocated
==11442== 
==11442== LEAK SUMMARY:
==11442==    definitely lost: 0 bytes in 0 blocks
==11442==    indirectly lost: 0 bytes in 0 blocks
==11442==      possibly lost: 0 bytes in 0 blocks
==11442==    still reachable: 192 bytes in 1 blocks
==11442==         suppressed: 0 bytes in 0 blocks

如果不是为什么在一个 block 中仍然存在内存泄漏？

这是我的代码:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
/*check definition of _OPENMP*/
#ifdef _OPENMP
#include <omp.h>
#endif 

#define RMAX 10000000

/*Global variables*/
int arraySizeGlobal;
int numberOfthreads;
int *aux;

/*Functions*/
void sort(int *a);
void sort2(int *a, int lo, int hi);
void merge(int *a, int lo, int mid, int hi);
void Generate_list(int a[], int n);
void printlist(int *array);

int main(int argc, char* argv[])
{
numberOfthreads = strtol(argv[1], NULL, 10);
arraySizeGlobal = strtol(argv[2], NULL, 10);
////////////////////////////////
int *array;
array = malloc(arraySizeGlobal * sizeof(int));
Generate_list(array,arraySizeGlobal);

printf("=====================\n");
printf("////Starting list////\n");
printf("=====================\n");
printlist(array);

sort(array);

printf("=====================\n");
printf("/////Sorted list/////\n");
printf("=====================\n");
printlist(array);

free(array);

return 0;
}

void sort(int *a)
{
aux = malloc(arraySizeGlobal * sizeof(int)); // Allocate space just once.
//#pragma omp parallel num_threads(numberOfthreads)
//#pragma omp single nowait
sort2(a, 0, arraySizeGlobal - 1);
free(aux);
}
void sort2(int *a, int lo, int hi)
{   // Sort a[lo..hi].
if (hi <= lo) return;
int mid = lo + (hi - lo)/2;
    #pragma omp parallel sections num_threads(numberOfthreads)
    {
    #pragma omp section
    sort2(a, lo, mid); // Sort left half.
    #pragma omp section
    sort2(a, mid+1, hi); // Sort right half.
    }

merge(a, lo, mid, hi); // Merge
}
void merge(int *a, int lo, int mid, int hi)
{   // Merge a[lo..mid] with a[mid+1..hi].
int i = lo, j = mid+1;
int k;
#pragma omp parallel for num_threads(numberOfthreads)
for (k = lo; k <= hi; k++) // Copy a[lo..hi] to aux[lo..hi].
    aux[k] = a[k];
for (k = lo; k <= hi; k++) // Merge back to a[lo..hi].
    if (i > mid) a[k] = aux[j++];
    else if (j > hi ) a[k] = aux[i++];
    else if (aux[j] < aux[i]) a[k] = aux[j++];
    else a[k] = aux[i++];
}
void printlist(int *array)
{
int i;
for (i = 0; i < arraySizeGlobal; ++i)
{
    printf("%d ", array[i]);
}
printf("\n");
}
void Generate_list(int a[], int n) {
int i;
srandom(1);
for (i = 0; i < n; i++)
    a[i] = random() % RMAX;
}  /* Generate_list */

============================================= ===================================

此代码:来自算法第四版，Robert Sedgewick |凯文·韦恩。这是一个java实现，我将其更改为c实现并用openmp瘫痪

============================================= ===================================

Answer 1

这在很大程度上取决于您的编译器和 openmp 库实现。

我用 gcc -fopenmp 版本 4.4.6 (GCC) 和 libgomp 1.0.0 尝试了你的代码，我也得到了尚未释放的堆 block 。据我所知，libgomp 不会在执行结束时杀死它生成的线程，并让内核清理执行此操作。

==85122== HEAP SUMMARY:
==85122==     in use at exit: 2,072 bytes in 4 blocks
==85122==   total heap usage: 203 allocs, 199 frees, 289,816 bytes allocated
==85122== 
==85122== 288 bytes in 1 blocks are possibly lost in loss record 3 of 4
==85122==    at 0x4A05A28: calloc (vg_replace_malloc.c:467)
==85122==    by 0x3793A11792: _dl_allocate_tls (in /lib64/ld-2.12.so)
==85122==    by 0x379460701F: pthread_create@@GLIBC_2.2.5 (in /lib64/libpthread-2.12.so)
==85122==    by 0x4C15509: gomp_team_start (team.c:422)
==85122==    by 0x400BAA: sort2 (in /usr/users/ga002/lamzins/malloc_openmp)
==85122==    by 0x400B28: sort (in /usr/users/ga002/lamzins/malloc_openmp)
==85122==    by 0x400AAA: main (in /usr/users/ga002/lamzins/malloc_openmp)
==85122== 
==85122== LEAK SUMMARY:
==85122==    definitely lost: 0 bytes in 0 blocks
==85122==    indirectly lost: 0 bytes in 0 blocks
==85122==      possibly lost: 288 bytes in 1 blocks
==85122==    still reachable: 1,784 bytes in 3 blocks
==85122==         suppressed: 0 bytes in 0 blocks
==85122== Reachable blocks (those to which a pointer was found) are not shown.
==85122== To see them, rerun with: --leak-check=full --show-reachable=yes
==85122== 
==85122== For counts of detected and suppressed errors, rerun with: -v
==85122== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 6)

当我使用 icc -openmp 版本 12.0.2 编译您的代码时，我释放了所有分配的内存。

==85218== HEAP SUMMARY:
==85218==     in use at exit: 0 bytes in 0 blocks
==85218==   total heap usage: 841 allocs, 841 frees, 4,364,204 bytes allocated
==85218== 
==85218== All heap blocks were freed -- no leaks are possible

编辑:您描述的问题也是已知的，不被视为内存泄漏:http://gcc.1065356.n5.nabble.com/Bug-libgomp-36298-New-gomp-contains-small-memoryleak-td330804.html