[MXNET-1415]Add MXEnginePushAsyncND and MXEnginePushSyncND C APIs

[wkcn]

Description

Hi, there.
In the PR #14615, @yuxihu added Add MXEnginePushAsync and MXEnginePushSync C APIs.

MXEnginePushAsync and MXEnginePushSync needs VarHandles of NDArrays.
However, MXNet doesn't expose the API to get the VarHandle of a NDArray.

After the discussion with @szha, We considered that it's more elegant to add MXEnginePushAsyncND and MXEnginePushSyncND C APIs, whose arguments are NDArrayHandles, rather than VarHandles.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http:https://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• Add MXEnginePushAsyncND and MXEnginePushSyncND C APIs
• Add the related unittest.
• Add a simple example: https://github.com/wkcn/test_mx_sync

[leleamol]

The proposed APIs are not part of cpp-package C++ API. Hence removing the "C++" label.
@mxnet-label-bot remove [C++]

[anirudh2290]

@wkcn What is the additional use case for this apart from horovod ? Is this going to be changed in horovod ?

[wkcn]

@anirudh2290 I will write a use case to test the two APIs : ), and it does not change Horovod. It is useful for Horovod to avoid including different versions of ndarray header file. In addition, it will be better for TVM and other third-party libraries.

I write a custom operator library MobulaOP (https://github.com/wkcn/mobulaop), and I found that there is not any way to use the asynchronous execution of MXNet. Although we can use TVMBridge API (https://github.com/apache/incubator-mxnet/blob/master/src/nnvm/tvm_bridge.cc#L174) to create an asynchronous function, there is an ABI compatibility problem (We discussed it on TVM forum https://discuss.tvm.ai/t/the-abi-compatibility-of-packedfunc/1601), because TVMBridge uses the C++ class PackedFunc with std::function object.

[anirudh2290]

@wkcn thank you for providing the details!

[wkcn]

Hi, @anirudh2290 . I have written a simple example to show hot to use these two APIs.
https://github.com/wkcn/test_mx_sync

Test Procedure:

1. Build MXNet with this PR
2. git clone https://github.com/wkcn/test_mx_sync && cd test_mx_sync
3. make
4. python test_sync.py