[REVIEW] Add a public copy API to DeviceBuffer

[galipremsagar]

Description

This PR adds a public copy API to DeviceBuffer, this is required for the ongoing copy-on-write work in rapidsai/cudf#11718

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[bdice]

It might be worth thinking about implementing or using the __copy__ or __deepcopy__ methods used by Python's copy module. See:

• https://docs.python.org/3/library/copy.html
• https://stackoverflow.com/questions/1500718/how-to-override-the-copy-deepcopy-operations-for-a-python-object

[shwina]

It might be worth thinking about implementing or using the copy or deepcopy methods used by Python's copy module.

In general, the SciPy/PyData ecosystem seems to have shied away from this model, instead providing explicit copy() methods for its types. In practice, I really only ever reach for copy() and deepcopy() for builtin types. I'd be curious if this has been your experience as well, @bdice?

[bdice]

It might be worth thinking about implementing or using the copy or deepcopy methods used by Python's copy module.

In general, the SciPy/PyData ecosystem seems to have shied away from this model, instead providing explicit copy() methods for its types. In practice, I really only ever reach for copy() and deepcopy() for builtin types. I'd be curious if this has been your experience as well, @bdice?

Interestingly, NumPy defines both: https://numpy.org/doc/stable/reference/generated/numpy.ndarray.__deepcopy__.html

I don’t have strong feelings here. Just wanted to mention that that object model exists, in case someone wants to use Python’s copy module to (deep) copy an arbitrary object containing a DeviceBuffer.

[shwina]

I suppose we could follow suit and implement __depcopy__ for people doing something like deepcopy([buf1, buf2]) (in addition to an explicit copy() method).

[galipremsagar]

I suppose we could follow suit and implement __depcopy__ for people doing something like deepcopy([buf1, buf2]) (in addition to an explicit copy() method).

Added a __deepcopy__ in addition to copy

[bdice]

Looks good, just some minor clarifications about deep/shallow copying before I approve.

[bdice]

LGTM, one minor question.

[galipremsagar]

@gpucibot merge