Asyncify the client

[tomaka]

Right now the client is synchronous. This is particularly bad for light client requests, which just block the current thread.

Considering the difficulty of doing this, there's no point in tackling this issue before async/await are stable.

[tomaka]

Alternatively, we could debate changing the architecture to make the Client correspond to a full-client only, and use another layer on top of the Client when we need to abstract over both full and light clients.

[gterzian]

Do you have an example of a current sync api, and how it would look once "asyncified"?

[tomaka]

The offenders are:

• substrate/core/client/src/light/backend.rs

  Line 361 in 9505713

  futures::executor::block_on(

• substrate/core/client/src/light/blockchain.rs

  Line 124 in 9505713

  futures::executor::block_on(

• substrate/core/client/src/light/blockchain.rs

  Line 161 in 9505713

  futures::executor::block_on(

• substrate/core/client/src/light/call_executor.rs

  Line 102 in bdc96e1

  futures::executor::block_on(self.fetcher.remote_call(RemoteCallRequest {

Instead of blocking waiting for the Future to resolve, we should also return a Future.
This probably propagate throughout the entire library and throughout Substrate. Whenever you need to fetch any information from the client, it would have be an asynchronous call.

[expenses]

Those specific calls were removed as of 8426cf1. Is there much that can be done for this at present?