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我读这个OpenMP tutorial,并遇到下面的程序:是否需要在OpenMP中将循环索引设置为私有变量?
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#define N 100
int main (int argc, char *argv[]) {
int nthreads, tid, i;
float a[N], b[N], c[N];
/* Some initializations */
for (i=0; i < N; i++)
a[i] = b[i] = i;
#pragma omp parallel shared(a,b,c,nthreads) private(i,tid)
{
tid = omp_get_thread_num();
if (tid == 0)
{
nthreads = omp_get_num_threads();
printf("Number of threads = %d\n", nthreads);
}
printf("Thread %d starting...\n",tid);
#pragma omp for
for (i=0; i<N; i++)
{
c[i] = a[i] + b[i];
printf("Thread %d: c[%d]= %f\n",tid,i,c[i]);
}
} /* end of parallel section */
}
我有点糊涂了循环索引i
是否必须是private
变量或没有。由于来自同一教程:
所有线程都可以修改和访问所有变量(除循环索引)
如此看来线程无法控制i
,是不是?顺便说一句,我试图从private
变量删除i
,结果似乎确定。