Blocking calls

[diocas]

I've observed that the call to retrieve the shares is blocking all the other calls to the backend, to the point JL freezes (and even shows an error). This makes the extensions completely unusable for me (and many others), since I have a lot of shares and the stats take a long time to finish (it takes ~1min to finish).

It also doesn't help that we're constantly retrieving the shares, even when not needed (check #161)

This syntom means that our API is not asynchronous and is blocking the main process. So we need to fix this ASAP (even if we remove the stats, this should be done).
I've done a very quick search and I believe there's an example on how to asynchronously call grpc: https://github.com/grpc/grpc/blob/master/examples/python/async_streaming/client.py

[dagl]

Steps required:

• investigate grpc and async
• implement a testing solution for jupyter backend to see how async improves responsiveness
  (a simple performance test with locust should be enough)
• start implementing async in the server
  • convert 1 method to async as POC
  • convert the rest