add a method to get a summary of available backends

[grlee77]

from the discussion in scipy/scipy#10383

should uarray have some sort of function to report what backends are currently global and/or registered?

[hameerabbasi]

@grlee77 Would you prefer this in the first version?

[grlee77]

I don't think it is critical, just something to consider potentially adding at some point.

[hameerabbasi]

cc @peterbell10 This is important for dask.distributed, not just getting, but setting global backend state.

I was thinking of the following approach:

• Transform the set of backends into an iterator of an internal type.
• Return the iterator of the type wrapped in Python when asked
• Provide a way to set the global state.

[peterbell10]

Can you explain what's different about dask.distributed?

[hameerabbasi]

The Python process is separate, possibly even on a different machine, but the context needs to be synchronized or passed to the child process.

[peterbell10]

So the whole of uarray's state needs to be persisted into another process. In that case it would probably be easiest to just return something like a dictionary of lists, otherwise the pickling would have to be handled manually.

[hameerabbasi]

That would be good, yes. 😄 I'm wonder if there's a way to do this with multiprocessing that doesn't involve modifying end-user code.

[hameerabbasi]

Internally, we should keep C++ native objects, so as not to degrade performance.

[hameerabbasi]

Is this resolved by #244 and #220? Or would such a list still be preferred?