Fixing race condition at Module::forward method (#21398)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21398
Module::forward method calls find_method() function potentially in multiple threads.
Internally it calls find_offset() method and reads dict_ object.
If the correspondent name is not in a dictionary thread call insert() method and modifies dict_ object.
At the same time when first thread modifies dict_ object another thread can enter forward()->find_method()->find_offset() path
and access dict_ object for reading while it have been modified -> crash.
Moved mutex protection up to protect both calls find_offset() and insert().
Consider to use C++ 17 shared_mutex locking object instead of recursive_mutex object.
Reviewed By: bddppq
Differential Revision: D15638942
fbshipit-source-id: ca6a453448302a0b3666c87724755fa4e9ce242f
