nested classes with pointers woth openACC - gpu

Question

I have a rather big code in C++, I had to integrate some new class to the base class as shown below.
class A
{
int N;
B b;
double *__restrict__ w;
construct();
}
A::construct()
{
w=new double[N];
#pragma acc data enter create(this)
#pragma acc update device(this)
#pragma acc data enter create(w)
// allocate class A
b.construct()
}
class B
{
double *__restrict__ u;
double *__restrict__ v;
B(){};
construct();
}
B::construct()
{
u=new double[N];
v=new double[N];
#pragma acc data enter create(this)
#pragma acc update device(this)
#pragma acc data enter create(u)
#pragma acc data enter create(v)
}
I think I am running into the deep copy issue as the pointers of class B are invalidated and hence the behavior of the code on GPU i undefined.
I would appreciate the feedback on how to perform the class inclusion in another class without getting into the deep copy issue. I suspect the update device (this) somehow causes this.

Answer 1

Do you have a full example which recreates the error you're seeing? I wrote a little test example using your code snip-it and it worked fine. (See below)
If you were updating the "this" pointer after creating the arrays, then it would be a problem since you'd be overwriting the device pointers with the host pointers. But as you show above, it shouldn't be an issue.
% cat test.cpp
#include <iostream>
class B
{
public:
int N;
double *__restrict__ u;
double *__restrict__ v;
void construct(int);
};
void B::construct(int _N)
{
N=_N;
u=new double[N];
v=new double[N];
#pragma acc enter data create(this)
#pragma acc update device(this)
#pragma acc enter data create(u[:N])
#pragma acc enter data create(v[:N])
}
class A
{
public:
int N;
B b;
double *__restrict__ w;
void construct(int);
};
void A::construct(int _N)
{
N=_N;
w=new double[N];
#pragma acc enter data create(this)
#pragma acc update device(this)
#pragma acc enter data create(w[:N])
// allocate class A
b.construct(N);
}
int main() {
A myA;
int N=32;
myA.construct(N);
#pragma acc parallel loop present(myA)
for (int i=0; i<N; ++i) {
myA.w[i] = i;
myA.b.u[i] = i;
myA.b.v[i] = i;
}
#pragma acc update host( myA.w[:N], myA.b.u[:N], myA.b.v[:N])
for (int i=0; i<N; ++i) {
std::cout << myA.w[i] << ":" << myA.b.u[i] << ":" << myA.b.v[i] << std::endl;
}
return 0;
}
% pgc++ test.cpp -Minfo=accel -V18.10 -ta=tesla; a.out
main:
49, Generating present(myA)
Accelerator kernel generated
Generating Tesla code
52, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */
56, Generating update self(myA.b.u[:N],myA.w[:N],myA.b.v[:N])
B::construct(int):
21, Generating update device(this[:1])
Generating enter data create(this[:1],v[:N],u[:N])
A::construct(int):
41, Generating update device(this[:1])
Generating enter data create(w[:N],this[:1])
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