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Bug 1049 - std::make_shared fails to fulfill structure aliment
Summary: std::make_shared fails to fulfill structure aliment
Status: RESOLVED WORKSFORME
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - general (show other bugs)
Version: 3.2
Hardware: x86 - 32-bit All
: Lowest Feature Request
Assignee: Nobody
URL:
Whiteboard:
Keywords:
Depends on:
Blocks: 3.4
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Reported: 2015-07-29 10:15 UTC by Valentin Roussellet
Modified: 2019-02-18 20:31 UTC (History)
4 users (show)



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Description Valentin Roussellet 2015-07-29 10:15:02 UTC
As described in the doc, structures having Eigen aligned members (e.g. Vector4) may be misaligned when created on the heap with new.

http://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html

The solution for that issue is to overload the operator new, which is provided as a convenience macro to add in the said struct.

However std::make_shared ignores the overladed operator new as, in at least two implementations of the STD (GNU and MSCV) actually calls the global ::new.

These two codes, while semantically equivalent, behave differently.

std::shared_ptr<Foo> = std:::make_shared<Foo>(...)
std::shared_ptr<Foo> = std:::shared_ptr<Foo>(new Foo(...))

The second one yielding correct alignment while the first one may return a non-aligned pointer.

Would another macro specializing std::make_shared for all types requiring alignment be useful or practical ? 

If not, should Eigen provide a make_aligned_shared<T> implementation ?
Comment 1 Gael Guennebaud 2015-08-08 10:00:16 UTC
In C++11 there is std::allocate_shared that you can use with Eigen's aligned allocator.
Comment 2 Christos 2017-06-14 05:35:27 UTC
(In reply to Gael Guennebaud from comment #1)
> In C++11 there is std::allocate_shared that you can use with Eigen's aligned
> allocator.

std::allocate_shared fails as well in VS2017.
Not sure if it specific to msvc or not.

The code below is enough to reproduce it

class Foo
{
   Vec4d v;
public:
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
};

auto test = std::allocate_shared<Foo>(Eigen::aligned_allocator<Foo>());
Comment 3 Gael Guennebaud 2019-02-18 20:31:52 UTC
Sorry for get back so late.

Works for me with gcc/clang (while make_shared does fail as expected).

If it don't work with MSVC, then this needs to be reported to VS team.

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