exercise2

Lecture 4 - Exercise 2

Result

cuda-memcheck --tool synccheck syncthreads

========= ERROR SUMMARY: 32 errors

32 invalid __syncthreads() calls were detected in the program (Barrier error detected. Divergent thread(s) in block).

Solution

From:

    // read values and increase if not already 2
    if(arr[idx] != 2) {
        local_array[threadIdx.x] = arr[idx] + 1;  
        __syncthreads();
    } else {
        local_array[threadIdx.x] = arr[idx];
        __syncthreads();
    }

To:

    // read values and increase if not already 2
    if(arr[idx] != 2) {
        local_array[threadIdx.x] = arr[idx] + 1;  
    } else {
        local_array[threadIdx.x] = arr[idx];
    }
    __syncthreads();

This change ensures that all threads in the block reach the __syncthreads() call, avoiding the barrier error.