Accessing value of device_vector build with a functional : error I don't understand

Question

I have a weird error that I don't understand when I initialize a device vector using a functional.

I want to create a device_vector of size 1000 with elements: A[i] = i*0.05;

Here is my code: (seen from example here : Thrust - Initial device_vector)

#include <thrust/device_vector.h>
#include <thrust/functional.h>  
#include <thrust/iterator/counting_iterator.h>
using namespace thrust::placeholders;

int main(void)
{
    thrust::device_vector<float> A(
        thrust::make_transform_iterator(
                thrust::counting_iterator<float>(0),_1*0.05),
        thrust::make_transform_iterator(
                thrust::counting_iterator<float>(0),_1*0.05) + 1000);

    std::cout << "--------------------------" << std::endl;
    std::cout << "A[0] is : " << A[0] << std::endl;
    std::cout << "A[1] is : " << A[1] << std::endl;
    std::cout << "A[100] is : " << A[100] << std::endl;
    std::cout << "A[500] is : " << A[500] << std::endl;

    return 0;
}

The code compiles fine (using thrust v1.6), but when I try to access any value of my device vector (such as A[0]), I get a runtime error.

What am I doing wrong? This is probably very basic, but it's late Friday night, and somehow I can't see it!

Thanks a lot for the help.

Answer 1

Thrust programs frequently will not behave correctly when compiled with the -G switch, so it's recommended not to use that with thrust.

This specific behavior may vary with thrust versions, and may improve over time with newer thrust versions. But in general, at the moment if you're having trouble with thrust code, try compiling without the -G switch.

Device code will frequently run faster when compiled without the -G switch as well, so in general -G should only be used when you expect to do device code debugging (e.g. with Nsight VSE or cuda-gdb), and there may also be other special cases where you want to use -G for test purposes, if you are focusing specifically on some aspect of device code generation. Otherwise, you should not compile codes with -G as a general practice.