Variable is now a subclass of at::Tensor backed by a VariableImpl* pImpl. The implementation of the ATen functions is defined in the auto-generated VariableType.h/cpp file.
Currently, only functions which fall through to the base type, such as sizes() and isCuda() are implemented. Differentiable ops like add() and mul() will be added in a subsequent PR.
Because of this Variables can no longer appear in the graph.
Every usage of a leaf Variable will leave an AccumulateGrad
function that has no outputs, but modifies var.grad as a side
effect.
The core autograd Variable, Function, and Engine no longer depend on the
Python API. This let's us implement functions in C++. In the future, we
can also multithread engine and release the GIL for most of the
non-Python backwards.
The register hook calls now return an object that can be used to remove
the hook. For example,
>>> h = module.register_forward_hook(callback)
>>> h.remove() # removes hook
Or as a context manager:
>>> with module.register_forward_hook(callback):
... pass
This makes it easier for libraries to use hooks without worrying about
name collisions.
Only references to their data and version counters are stored.
Also, it is now possible to have None arguments in save_for_backward
and return too many values from backward (as long as the excessive
results are None).
Without the PyObject_GC_UnTrack call, the tp_dealloc handler could get
called twice if a referred to object triggers a garbage collection from
its destructor.
See http://bugs.python.org/issue28737
