How to carry out a counter number in parallel_for_each - c++-amp

Question

1)Why the variable length in my sample code are not 62 after calculate ? It's
seems every time the condition is satisfied,but enter the condition,
the number "length not be added every single time.
2)If I don't use concurrency::array length(1, 1, &V[0]); to save counter
but using tile_static int, the length is also wrong.
//if my 8 x 8 local data are:
//cache[TS][TS]
//{
// -69, 0, 0, 1, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0,
// 0, 0, 0, 0, 0, 0, 0, 0
//}
My sample code:
void sample()
{
std::vector<int> V;
V.push_back(0);
concurrency::array<int, 2> length(1, 1, &V[0]);
const int TS = 8;
concurrency::parallel_for_each(data.extent.tile<TS, TS>(), [=, &length](tiled_index<TS, TS> index) restrict(amp)
{
const int row = index.local[0];
const int col = index.local[1];
//tile_static int length; ---------2)
tile_static int cache[TS][TS];
cache[row][col] = data[index.global];
index.barrier.wait();
if (cache[row][col] == 0)
{
//length++; -------------------2)
length[0][0] = length[0][0] + 1;
}
});
}

Answer 1

std::vector<int> V;
for (int i = 0; i < 256; i++)
V.push_back(0);
concurrency::array_view<int, 1> AC_count(256, &V[0]);
const int TS = 8;
concurrency::parallel_for_each(data.extent.tile<TS, TS>(), [=, &length](tiled_index<TS, TS> index) restrict(amp)
{
const int row = index.local[0];
const int col = index.local[1];
tile_static int cache[TS][TS];
cache[row][col] = data[index.global];
index.barrier.wait();
if (cache[row][col] == 0)
{
atomic_fetch_add(&AC_count[0], 1);
}
});
}