How to prevent thrust::copy_if illegal memory access - cuda

Question

In a CUDA C++ code, I am using thrust::copy_if to copy those integer values that are not -1 from the array x to y:
thrust::copy_if(x_ptr, x_ptr + N, y_ptr, is_not_minus_one());
I put the code in a try/catch and I update the array x regularly, and again push numbers that are not -1 to the end of the y until it accessed to the out of the array and returns
CUDA Runtime Error: an illegal memory access was encountered
As I don't know how many values are not -1 in each iteration, I should keep generating and copying numbers in the main array until it becomes full. However, I wanna it to stop once it reaches the end of the array. How can I manage it?
A naive idea would be using another array and then copying if the number of new values does not exceed the size. but it might be inefficient. Any better idea?

Answer 1

Here is one possible method:
use remove_if() instead, (with the opposite condition - remove if -1) on x. Then use (x start and) the returned iterator to copy to your final array (y). Every time you do a copy to y, you will know how much space is left in y, and you can adjust the copy quantity if needed, before doing the copy.
Example (removing 1 values):
$ cat t2088.cu
#include <thrust/device_vector.h>
#include <thrust/host_vector.h>
#include <thrust/complex.h>
#include <thrust/transform.h>
#include <thrust/copy.h>
#include <thrust/functional.h>
#include <iostream>
using mt = int;
using namespace thrust::placeholders;
int main(){
thrust::device_vector<mt> a(5);
thrust::device_vector<mt> c(25);
bool done = false;
int empty_spaces = c.size();
int copy_start_index = 0;
while (!done){
thrust::sequence(a.begin(), a.end());
int num_to_copy = (thrust::remove_if(a.begin(), a.end(), _1 == 1) - a.begin());
int actual_num_to_copy = std::min(num_to_copy, empty_spaces);
if (actual_num_to_copy != num_to_copy) done = true;
thrust::copy_n(a.begin(), actual_num_to_copy, c.begin()+copy_start_index);
copy_start_index += actual_num_to_copy;
empty_spaces -= actual_num_to_copy;
}
std::cout << "output array is full!" << std::endl;
thrust::host_vector<mt> h_c = c;
thrust::copy(h_c.begin(), h_c.end(), std::ostream_iterator<mt>(std::cout, ","));
std::cout << std::endl;
}
$ nvcc -o t2088 t2088.cu
$ compute-sanitizer ./t2088
========= COMPUTE-SANITIZER
output array is full!
0,2,3,4,0,2,3,4,0,2,3,4,0,2,3,4,0,2,3,4,0,2,3,4,0,
========= ERROR SUMMARY: 0 errors
$