[shortfin] Fix mobilenet_server example by filling mapped storage.

[ScottTodd]

I saw this error trying to run this example:

RuntimeError: Async exception on <Worker 'device-hostcpu:0:0@0'>): '_shortfin_default.lib.array.storage' object has no attribute 'data'

I looked around for and API that would allow for copying from array.array (https://docs.python.org/3/library/array.html) into shortfin's array.storage (https://shortfin.readthedocs.io/en/latest/reference.html#shortfin_default.lib.array.storage) and only found map().

Quite possible that I'm missing something, or there is an easier interface that isn't fully plumbed through to Python and the documentation yet.

Logs of this running: https://gist.github.com/ScottTodd/da8c1d6805584490c46e4d2086404a6b

[stellaraccident]

Grrg. Yeah, these low level transfer methods need an upgrade. Up until the most recent commit, I didn't have the device level metadata I needed to determine the right way to load data on to the device (i.e. map, transfer, chunk, etc). Now that I have that, need to design a more ergonomic API.

With that said, I believe that mapping.fill(buffer) will do what you want if the buffer is the size of the target (i.e. it will copy x1 vs tile). There are some tests that exercise that.

So I think you can say:

with self.host_staging.storage.map(write=True, discard=True) as m:
  m.fill(request.raw_image_data)

(assuming sizes line up)

[ScottTodd]

Nice, fill works. I saw that API and thought it would only work for a pattern of bytes, based on my read the docs: https://shortfin.readthedocs.io/en/latest/reference.html#shortfin_default.lib.array.storage.fill (also seems like docs are missing for the result of map()... should make sure we have cross reference links between all the types).