Can I remove the union definition in struct LinkedList?

[happynear]

In object_pool.h, line 48, there is a struct with a union in it:

  struct LinkedList {
    union {
      LinkedList* next{nullptr};
      T t;
    };
  };

In my environment (VS2013), the compiler cannot accept a union containing a class with a copy constructor. Can I remove the union definition, such as

  struct LinkedList {
      LinkedList* next{nullptr};
      T t;
  };

, or I must use boost::variant to replace it?

[tqchen]

No, you cannot remove the union def, I think you can move the type T ahead of the next, and see if that works for you. To change it to

 struct LinkedList {
      T t;
      LinkedList* next{nullptr};
  };

[happynear]

Thanks, now I come across an invalid pointer problem and it's difficult to debug.
I will keep an eye on mxnet and try again after it is formally released.

[happynear]

I have found where the invalid pointer locates.
In ndarray.h, line 470:

  inline NDArrayFunctionReg &set_function(void fsetvalue(const real_t &rhs,
                                                         NDArray *out)) {
    body = [fsetvalue] (NDArray **used_vars, real_t *s, NDArray **mutate_vars) {
      fsetvalue(s[0], mutate_vars[0]);
    };

When the program goes to fsetvalue, it seems that the fsetvalue is no longer the one registered to function list. When I replace the formal paramter with std::function, the problem solved.

  inline NDArrayFunctionReg &set_function(std::function<void (const real_t &rhs,
    NDArray *out)> fsetvalue) {
    body = [fsetvalue] (NDArray **used_vars, real_t *s, NDArray **mutate_vars) {
      fsetvalue(s[0], mutate_vars[0]);
    };

I started to learn C++11 just a few days ago, so I don't know why it works.

[tqchen]

Interesting, Thanks for investigation! There is nothing that I am aware of preventing us using function pointer instead of std::function. This might due to the fact that the registered ScalatSetValueOp was an inline function.

I updated the code in #160 Please check the updated code after it merged in

[happynear]

I am sadly to say, removing inline does not work. The two pointer adress are still different.

When set_value method is registered:

When the fsetvalue is called from python:

I have written some codes to replace the function pointer with std::function, however, in an inelegant way:
https://github.com/happynear/mxnet/blob/windows/include/mxnet/ndarray.h#L465
https://github.com/happynear/mxnet/blob/windows/src/ndarray/ndarray.cc#L508

I know you guys will find a better solution. I am waiting for it.

[tqchen]

OK, this could due to a fact that MSVC do not interpret function as function pointers I have pushed a change in tqchen@516a90a to fix this . Please check if that works for you after it is merged in #181

[happynear]

Yes it works. Thank you.

[tqchen]

If you are interest, we would love to get your contribution to make mxnet windows compatible with minimum changes. @jermainewang is working on a CMake build script to generate windows solutions, which you may be interested in collaborating

[happynear]

I have sent a pull request #183. I created the visual studio solution with imitation of https://github.com/dmlc/cxxnet/tree/master/windows . Please check and merge it.