Add latency simulation to Virtual workers

[LaRiffle]

Describe the solution you'd like
It would be great to add an option to simulate latency on virtual workers while sending message.
Basically just add a small sleep in the _recv_msg or _send_msg virtual worker methods.

[jefersonf]

What do you mean by latency simulation? Would it be an new option to a VirtualWorker like add_latency=100?. Like the following example.

...
import time

class VirtualWorker(BaseWorker, FederatedClient):
    def _send_msg(self, message: bin, location: BaseWorker, latency: int = 0) -> bin:
        time.sleep(latency)
        return location._recv_msg(message)

[BBloggsbott]

I'd like to implement this

[jefersonf]

Hi @BBloggsbott, I tried to tackle this. And I've actually started on, if you would like to give some help please take a look at this branch.

In fact, the following case is working so far:

import torch
import syft as sy
hook = sy.TorchHook(torch)

alice = sy.VirtualWorker(id="alice", hook=hook)
bob  = sy.VirtualWorker(id="bob", hook=hook)
x = torch.tensor([1,2,3])

# alice waits 2 seconds before sending 'x' to bob.
alice.send(x, bob, pending_time=2)

[BBloggsbott]

@jefersonf Why not just use the change you mentioned here? I feel only the virtual workers will need to simulate latency.

[jefersonf]

@jefersonf Why not just use the change you mentioned here? I feel only the virtual workers will need to simulate latency.

At first I thought so too, but I think in cases where a tensor is sent to a worker like in the following:

torch.tensor([1,2,3]).send(alice, pending_time=2)

the same behavior should be hold.

[BBloggsbott]

Ah. Okay.

How can I help with this?