How can I use parallel_for to pass two dimensional arrays?

yingemmachen — Tue, 08 Jun 2010 15:42:19 GMT

Hi,

I tried to use parallel_for to speed up our c++ program. It seems very easy to use. However, in the function which is to be parallelized, a few 2D arrays calculated in the function need be passed to the main funciton. In the example (sub_string_finder.cpp), one dimensional arrays are modified in the SubStringFinder by using the addresses of these arrays. Please see the code below. I am wondering if I can use similar trick, but not sure how to use it on 2D arrays.

Thanks,
Ying

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#include
#include
#include

#include "tbb/parallel_for.h"
#include "tbb/blocked_range.h"

using namespace tbb;
using namespace std;

static const size_t N = 23;

class SubStringFinder {
const string str;
size_t *max_array;
size_t *pos_array;
public:
void operator() ( const blocked_range& r ) const {
for ( size_t i = r.begin(); i != r.end(); ++i ) {
size_t max_size = 0, max_pos = 0;
for (size_t j = 0; j < str.size(); ++j)
if (j != i) {
size_t limit = str.size()-( i > j ? i : j );
for (size_t k = 0; k < limit; ++k) {
if (str[i + k] != str[j + k]) break;
if (k > max_size) {
max_size = k;
max_pos = j;
}
}
}
max_array = max_size;
pos_array = max_pos;
}
}
SubStringFinder(string &s, size_t *m, size_t *p) :
str(s), max_array(m), pos_array(p) { }
};

int main(int argc, char *argv[]) {

string str = { string("a"), string("b") };
for (size_t i = 2; i < N; ++i) str = str[i-1]+str[i-2];
string &to_scan = str[N-1];

size_t *max = new size_t[to_scan.size()];
size_t *pos = new size_t[to_scan.size()];

parallel_for(blocked_range(0, to_scan.size(), 100),
SubStringFinder( to_scan, max, pos ) );

for (size_t i = 0; i < to_scan.size(); ++i)
cout << " " << (int)max << "(" << (int)pos << ")" << endl;
delete[] max;
delete[] pos;
return 0;
}

How can I use parallel_for to pass two dimensional arrays?

yingemmachen — Wed, 09 Jun 2010 22:04:32 GMT

Hi,

I found a way to get around the problem. Just pass one dimensional arrays and convert them to two dimensional arrays later.

Ying

How can I use parallel_for to pass two dimensional arrays?

jimdempseyatthecove — Wed, 09 Jun 2010 23:45:56 GMT

Usualy you iterate on the row index.

topic How can I use parallel_for to pass two dimensional arrays? in Intel® Moderncode for Parallel Architectures

How can I use parallel_for to pass two dimensional arrays?

How can I use parallel_for to pass two dimensional arrays?

How can I use parallel_for to pass two dimensional arrays?