vectorAddMMAP target does not compile due to virtual memory feature set_access_mode

[Q-Minh]

The example target vectorAddMMAP has the error cuda-api-wrappers\examples\modified_cuda_samples\vectorAddMMAP\vectorAddMMAP.cpp(163,107): error C2665: 'cuda::memory::virtual_::set_access_mode': none of the 2 overloads could convert all the argument types when compiling with MSVC using VS2019.

[eyalroz]

Why couldn't they? What are the types MSVC is seeing? :-(

[Q-Minh]

There is an ambiguous call to either:

template <template <typename... Ts> class ContiguousContainer>
inline void set_access_mode(
	mapping_t mapping,
	const ContiguousContainer<device_t>& devices,
	access_mode_t access_mode);

or

template <template <typename... Ts> class ContiguousContainer>
void set_access_mode(
	region_t fully_mapped_region,
	const ContiguousContainer<device_t>& devices,
	access_mode_t access_mode);

in vectorAddMMAP.cpp line 163. This is quite weird, to be honest, looks like a compiler bug to me, since the signatures are quite obviously different, with mapping_t and region_t having no related inheritance tree or anything.

[eyalroz]

Maybe it's an issue with MSVC's support for template-template parameters.

What happens if we separate the two function names? i.e. set_mapping_access_mode() and set_region_access_mode()?

[Q-Minh]

Okay, so the actual problem was that std::iterator_traits<Iter> was not able to specialize Iter = enumerator<...>::const_iterator, because there were some typedefs/aliases missing. The fix is then to add:

using difference_type = std::ptrdiff_t;
using value_type = value_type;
using pointer = value_type*;
using reference = value_type&;
using iterator_category = std::forward_iterator_tag;

in the declaration of struct enumerator<Container>::iterator, and

using difference_type = std::ptrdiff_t;
using value_type = value_type;
using pointer = value_type const*;
using reference = value_type const&;
using iterator_category = std::forward_iterator_tag;

in the declaration of struct enumerator<Container>::const_iterator.

Now MSVC can disambiguate between the 2 overloads of set_access_mode(...).

[eyalroz]

Are you sure we need value_type? That looks redundant.

[Q-Minh]

Yeah, pretty sure, because std::iterator_traits<Iter> takes the iterator itself as template parameter, not the container, and it attempts to directly access member typedefs on the Iter type passed in. Based on cppreference, there are 5 required member typedefs, of which value_type is a part of.

[eyalroz]

How's this?

[Q-Minh]

How's this?

Looks good! I don't know about gcc and clang, but at least with msvc, you don't need to specify enumerator:: to capture the value_type of the enclosing enumerator class. However, if you do want to specify it, I would write enumerator<Container>::value_type instead.

[eyalroz]

@Q-Minh : Sure.