[swift-server-dev] Next HTTP API meeting
Carl Brown1
Carl.Brown1 at ibm.com
Mon Mar 27 12:07:01 CDT 2017
Hi, Tanner,
When I'm writing SSS code for an iOS endpoint that talks to a back-end
service, I'll often dispatch an URLSession.dataTask() to go ask the
back-end for data, and then request/response handling occurs in the
completion handler when the dataTask comes back.
I find that to be a really common pattern when I'm working in an Enterprise
and I have some kind of legacy service I need to talk to.
-Carl
From: Tanner Nelson via swift-server-dev <swift-server-dev at swift.org>
To: Chris Bailey <BAILEYC at uk.ibm.com>
Cc: swift-server-dev <swift-server-dev at swift.org>
Date: 03/27/2017 09:42 AM
Subject: Re: [swift-server-dev] Next HTTP API meeting
Sent by: swift-server-dev-bounces at swift.org
@chris in my experience there's been very little passing of
request/response between threads. Usually the server accepts, spins up a
new thread, and all HTTP parsing/serializing happens on that one thread.
Could you specify some examples where requests/responses are being passed
between threads?
That said, it should be fairly easy to implement threading to see what the
effects would be. I will look into that. :)
Tanner
Vapor
tanner at vapor.codes
On Mar 27, 2017, at 3:37 PM, Chris Bailey <BAILEYC at uk.ibm.com> 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
I found only a marginal increase in performance (~5%) in favor of
inout value types.
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
On Mar 27, 2017, at 1:55 PM, Michael Chiu via swift-server-dev <
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> 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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