use a new stream per request

[Stebalien]

"pipelining is hard, painful, and error-prone" is a key reason browsers gave up on it and started implementing stream muxing.

Guess what, we have stream muxing!

Now, this is what we used to do (i.e., we used to use one stream per request).

There are two reasons not to:

1. Setting up a stream is expensive. It's really not. Yes, we have to send a bunch of extra bytes but it usually doesn't even cost a round trip (we should have a guaranteed no round trip but, well, we don't).
2. No backpressure. We can and should fix this at a lower level (this should be a host<->host negotiation).

In terms of performance, I had to remove the lower latency bound in the test cases to get them to pass.

[Stebalien]

Note: This PR is intentionally inflammatory and exists for discussion.

[whyrusleeping]

show me the numbers

[Stebalien]

One stream per request:

Parallel PutValue calls (100) completed in 2.726807896s
Parallel GetValue calls (100) completed in 2.38722302s
Sequential PutValue calls (10) completed in 10.10373804s
Sequential PutValue calls (10) completed in 4.897108013sh

Pipelined:

Parallel PutValue calls (100) completed in 6.155222485s
Parallel GetValue calls (100) completed in 4.461936237s
Sequential PutValue calls (10) completed in 10.477949103s
Sequential GetValue calls (10) completed in 4.522981736s

Note: the timing can vary by up to a second. However, this patch is definitely faster in the mock net.

However, I don't know why we switched away from using one stream per request in the first place.

[whyrusleeping]

And bandwidth usage? (as tracked by the OS)

[Stebalien]

30%? WTF multistream select!

---

One of my plans for the libp2p meetup is to improve multistream-select. I'll add "low overhead" to the list. Ideally, identify would negotiate connection specific aliases that are just varints.

[whyrusleeping]

Yeah... this is why I did the stream reuse stuff in the first place. It makes me sad. Hear that @jbenet ?? SAD

[anacrolix]

Why was this closed? Was it due to extra bandwidth requirements?

[Stebalien]

Yes.