[swift-server-dev] Next HTTP API meeting

[Logan Wright]

Thanks Michael,

Those are good examples, just for records as people read along, the
reference alternative to these would be a non static value that is
constructed each time. To end user, it would be the same, with the
difference that the code is computed each time, so possibly a minor
performance hit if construction time > copy time.

I completely agree, I think protocols are the most flexible way to
implement the apis, I also believe that they're most in the spirit of the
group which is to create something adaptable to the various frameworks to
allow more code share for low level libraries. I haven't seen anything yet
that couldn't be accomplished with protocols and leave end implementations
up to consumers. This would allow us to really focus on the abstract values
returned by the parser and let the group move forward with the onus of
models on end users.

I think it's worth outlining some of the result of a parser in abstract
values, for example. The most basic HTTP Header based on our discussions
would be `[(String, String)]`, the most basic method would be `String`,
etc. Then we could see how a protocol based model would fit this. If we can
come up with some agreements there, generics and inlining could create some
pretty performant code without infringing on the creativity of various
frameworks.

- Logan

On Mon, Mar 27, 2017 at 3:38 PM Chris Bailey via swift-server-dev <
swift-server-dev at swift.org> wrote:

> Nice work!
>
> Taking a quick look at the project and screenshot, am I right in saying
> that there is no concurrency in the test? ARC generally has a bigger impact
> in concurrent use cases because of the need to keep memory consistency
> across processors for the atomic increment/decrement.
>
> How hard would it be to add a dispatch queue in?
>
> Chris
>
>
>
> From:        Tanner Nelson via swift-server-dev <
> swift-server-dev at swift.org>
> To:        Michael Chiu <hatsuneyuji at icloud.com>
> Cc:        swift-server-dev <swift-server-dev at swift.org>
> Date:        27/03/2017 14:38
> Subject:        Re: [swift-server-dev] Next HTTP API meeting
> Sent by:        swift-server-dev-bounces at swift.org
> ------------------------------
>
>
>
> Re: performance,
>
> I did a quick test of inout struct vs. class performance. The code can be
> found here: *https://github.com/tanner0101/request-types*
> <https://github.com/tanner0101/request-types>
>
> I found only a marginal increase in performance (~5%) in favor of inout
> value types. *https://github.com/tanner0101/request-types/issues/1*
> <https://github.com/tanner0101/request-types/issues/1>
>
> Additionally, non-inout value types were a lot slower. This is obvious to
> the seasoned Swift dev considering each middleware in the test modifies and
> thus must copy the request. But this is the exact type of performance issue
> you can expect developers to create when interacting with "non-obvious
> value types". HTTP request/response being non-obvious value types compared
> to something like an integer or a float. (I'd argue the majority of web
> developers would expect request/response to be a reference type and thus
> easily forget or not know to use `inout`)
>
> Please feel free to submit any prs/issues/comments about ways I could
> improve this test to make it more accurate.
>
> tl;dr: value types don't seem much faster than reference types (especially
> considering dangers of misuse) in a simulated web framework scenario
>
> inb4: people saying that the request/response models in my test are
> incomplete/not fully implemented/bad. this is _not_ a proposed api for
> request/response.
>
> Vapor
> *tanner at vapor.codes* <tanner at vapor.codes>
>
> On Mar 27, 2017, at 1:55 PM, Michael Chiu via swift-server-dev <
> *swift-server-dev at swift.org* <swift-server-dev at swift.org>> wrote:
>
>
> On Mar 27, 2017, at 5:13 AM, Logan Wright via swift-server-dev <
> *swift-server-dev at swift.org* <swift-server-dev at swift.org>> wrote:
> If people feel extremely strong that there needs to be a concrete type,
> then I'd like to push for reference type as much as possible. As far as
> reference vs value type, I haven't really heard an argument for value types
> beyond what feels like a reaction to value types being the hip new hotness.
> While yes, they're great in Swift, and there's tons of places that should
> absolutely be modeled with value semantics, a request/response interaction
> represents a single request and should definitely be a reference based
> interaction.
>
> I disagree with this one. First of all I think most of the framework pass
> the request and response as inout argument, if that is the case there
> shouldn’t be much copy overhead in the run loop. Second the problem of
> reference type is that everywhere the request and response exists could
> possibly mutate the res/req, and it affect globally. It is true that in
> normal use there shouldn’t be two place simultaneously operate on the same
> request but that could happen. (Therefore protocol is the best isn’t it)
>
> In practice, we went through several model iterations and the value type
> created very high levels of bugs and confusion for end users. The three
> biggest problems we had were as follows:
>
> - Greatly increased bug levels and confusion related to unexpected mutation
> - Unnecessary code requirements added to every single passive access (ie:
> middleware) increasing code bloat unnecessarily
> - Extreme performance loss due to massive copy overhead
>
> Each of these problems evaporated pretty instantaneously when moving to
> reference types; it made it significantly easier to reason about for end
> users.
> Just for curiosity, I’m very interested in the unexpected mutation of
> value semantic, I have always had an impression of value semantic are more
> free from unexpected mutation.
>
> Would like to remind again for those that skipped above reading that our
> goal is not to build a web framework here, but rather to build small tools
> that make building frameworks slightly easier for library maintainers and
> creators.
> That’s so true lol.
>
> Michael.
>
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