OpenMP code in CUDA source file not compiling on Google Colab - jupyter-notebook

Question

I am trying to run a simple Hello World program with OpenMP directives on Google Colab using OpenMP library and CUDA. I have followed this tutorial but I am getting an error even if I am trying to include %%cu in my code. This is my code-
%%cu
#include<stdio.h>
#include<stdlib.h>
#include<omp.h>
/* Main Program */
int main(int argc , char **argv)
{
int Threadid, Noofthreads;
printf("\n\t\t---------------------------------------------------------------------------");
printf("\n\t\t Objective : OpenMP program to print \"Hello World\" using OpenMP PARALLEL directives\n ");
printf("\n\t\t..........................................................................\n");
/* Set the number of threads */
/* omp_set_num_threads(4); */
/* OpenMP Parallel Construct : Fork a team of threads */
#pragma omp parallel private(Threadid)
{
/* Obtain the thread id */
Threadid = omp_get_thread_num();
printf("\n\t\t Hello World is being printed by the thread : %d\n", Threadid);
/* Master Thread Has Its Threadid 0 */
if (Threadid == 0) {
Noofthreads = omp_get_num_threads();
printf("\n\t\t Master thread printing total number of threads for this execution are : %d\n", Noofthreads);
}
}/* All thread join Master thread */
return 0;
}
And this is the error I am getting-
/tmp/tmpxft_00003eb7_00000000-10_15fcc2da-f354-487a-8206-ea228a09c770.o: In function `main':
tmpxft_00003eb7_00000000-5_15fcc2da-f354-487a-8206-ea228a09c770.cudafe1.cpp:(.text+0x54): undefined reference to `omp_get_thread_num'
tmpxft_00003eb7_00000000-5_15fcc2da-f354-487a-8206-ea228a09c770.cudafe1.cpp:(.text+0x78): undefined reference to `omp_get_num_threads'
collect2: error: ld returned 1 exit status
Without OpenMP directives, a simple Hello World program is running perfectly as can be seen below-
%%cu
#include <iostream>
int main()
{
std::cout << "Welcome To GeeksforGeeks\n";
return 0;
}
Output-
Welcome To GeeksforGeeks

Answer 1

There are two problems here:
nvcc doesn't enable or natively support OpenMP compilation. This has to be enabled by additional command line arguments passed through to the host compiler (gcc by default)
The standard Google Colab/Jupyter notebook plugin for nvcc doesn't allow passing of extra compilation arguments, meaning that even if you solve the first issue, it doesn't help in Colab or Jupyter.
You can solve the first problem as described here, and you can solve the second as described here and here.
Combining these in Colab got me this:
and then this: