Deadlock in LibMxNet.dll during unload due to synchronization call in destructor

[eftiquar]

Description

The destructor for "mxnet::Engine" local static instance calls into STL's condition_variable::notify_all , which in turn calls NtReleaseKeyedEvent, an undocumented Windows API which results in deadlock, as the call is being run with loader lock acquired, in the context of DLL unload machinery.
Independent of this hang, having non-trivial destructor for static local variable is recipe for unforeseen problems. These destructors are called in unspecified order, and may call into other DLLs or ( Shared Objects) that are unloaded.

(Brief description of the problem in no more than 2 sentences.)

Environment info (Required)

Windows 7, any MxNet build

Compiler (gcc/clang/mingw/visual studio):

Error Message:

No error message, the Python process hangs upon exit

Minimum reproducible example

(If you are using your own code, please provide a short script that reproduces the error. Otherwise, please provide link to the existing example.)

Steps to reproduce

1. Set up a standard Windows 7 system
2. Install Python from https://sourceforge.net/projects/winpython/files/WinPython_3.6/3.6.5.1/beta... ...
3. Run the following in the Windows Python command shell:
   a. pip install mxnet
   b. python
4. Run the following in the Python shell:
   a. import mxnet
   b. exit()

What have you tried to solve it?

Proposed solution

a. Provide explicit API to destroy the "mxnet::Engine" instance that is complement to Engine::Create.
b. Have LibMxNet consumers call Destroy API explicitly before exiting.
c. Modify the destructor to not perform cleanup, as Destroy will have already done that
d. If no one calls cleanup, it should not matter. As, after the process is destroyed, all the resources will be reclaimed by the OS

[anirudh2290]

Related to #8921 and #9271

[m-ky]

This should be the same as #8754. It's only win7. win10 works fine.
Could someone please take a look at this?

[apeforest]

@nswamy @sandeep-krishnamurthy Please add label [Call for Contribution]. This has been the rootcause of several issues

[larroy]

Let's close this. We can't invest energy on Windows 7. As I understand this doesn't happen in Windows 10.

[gmx1992]

Proposed solution
https://blog.csdn.net/CR_Alvin/article/details/110631788

[romintomasetti]

This is still happening as of MxNet 1.7.0 (on Windows 7), using the C++ or Python API.