Summary:
Python never closes shared library it `dlopen`s. This means that calling `load` or `load_inline` (i.e. building a JIT C++ extension) with the same C++ extension name twice in the same Python process will never re-load the library, even if the compiled source code and the underlying shared library have changed. The only way to circumvent this is to create a new library and load it under a new module name.
I fix this, of course, by introducing a layer of indirection. Loading a JIT C++ extension now goes through an `ExtensionVersioner`, which hashes the contents of the source files as well as build flags, and if this hash changed, bumps an internal version stored for each module name. A bump in the version will result in the ninja file being edited and a new shared library and effectively a new C++ extension to be compiled. For this the version name is appended as `_v<version>` to the extension name for all versions greater zero.
One caveat is that if you were to update your code many times and always re-load it in the same process, you may end up with quite a lot of shared library objects in your extension's folder under `/tmp`. I imagine this isn't too bad, since extensions are typically small and there isn't really a good way for us to garbage collect old libraries, since we don't know what still has handles to them.
Fixes https://github.com/pytorch/pytorch/issues/11398 CC The controller you requested could not be found.
ezyang gchanan soumith fmassa
Pull Request resolved: https://github.com/pytorch/pytorch/pull/11725
Differential Revision: D9948244
Pulled By: goldsborough
fbshipit-source-id: 695bbdc1f1597c5e4306a45cd8ba46f15c941383
