Clarification on using OpenACC in a shared library

Hi Pramod,

The work around would be to not use RDC (i.e. -gpu=nordc) with shared objects. However without RDC, the code can’t contain any static global references in “declare” directives, like extern variables, nor allows for cross-file device routine calls. So you’d need to reorganize the code so “my_data” is passed in as an argument, rather a global reference.

For example:

% cat test1.cpp
#include <stdlib.h>
#include <stdio.h>

void init(double val, float** my_data, double & my_celsius) {
    *my_data = (float*) malloc(sizeof(float)*3);
    (*my_data)[0] = 1.1;
    float * tmp = *my_data;
    #pragma acc enter data copyin(tmp[0:3])

    my_celsius = val;
    #pragma acc enter data copyin(my_celsius)

#pragma acc routine seq
double foo (double my_celsius,  double my_value) {
    double y = 2.0;
    // 2 + 5 + 1 = 8
    return y + my_celsius + my_value;

double sample(double & my_celsius,double my_value) {
  double val;
  #pragma acc serial present(my_celsius) copyout(val)
      val = foo(my_celsius, my_value);
  return val;
dev-sky5:/local/home/colgrove/tmp% cat main.cpp
#include <iostream>

void init(double val, float** my_data, double & my_celsius);
double sample(double &my_celsius,double my_value);
static double my_value = 1.0;

int main() {

    float * my_data;
    double my_celsius;
    double val = sample(my_celsius,my_value);
    std::cout << "Val=" << val << std::endl;
    std::cout << "Done\n";
    return 0;
% nvc++ -acc -Minfo -gpu=cc70 test1.cpp -c -fPIC
init(double, float **, double &):
     10, Generating enter data copyin(tmp[:3])
     12, Generating enter data copyin(my_celsius[:1])
foo(double, double):
     15, Generating acc routine seq
         Generating Tesla code
sample(double &, double):
     24, Generating present(my_celsius[:1])
         Generating copyout(val) [if not already present]
         Accelerator serial kernel generated
         Generating Tesla code
% nvc++ -acc -gpu=cc70 -shared -o test1.o
% nvc++ -acc main.cpp -gpu=cc70
% a.out