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Don't force completion blocks to be scheduled on the main queue
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Different request performers are allowed to have different semantics
when it comes to the queue that results are delivered on. If a performer
already happens to deliver results on the main queue, `APIClient` is
injecting latency by scheduling an unnecessary async call. If a
performer delivers results on a background queue (i.e., `NetworkRequestPerformer`),
and there's further processing that would benefit from occurring in the
background (e.g., image processing or decoding a large object), callers
must dispatch back onto a background queue to avoid blocking the UI. It
also hampers composability of requests, because multiple chained
requests will incur a penalty from jumping back and forth from the main
queue to a background queue.

This breaking change removes the `dispatc_async`, replacing it with the
more abstract idea of a `Scheduler`, which is a block that schedules the
completion handler to be performed, either synchronously or
asynchronously. The `mainQueueScheduler` is the default, and an
`immediateScheduler` is provided to synchronously invoke the completion
block instead.
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@sharplet
sharplet committed May 20, 2016
1 parent b5235f0 commit 460f087
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Showing 6 changed files with 86 additions and 22 deletions.
5 changes: 0 additions & 5 deletions Source/Extensions/GCD.swift
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This file was deleted.

8 changes: 5 additions & 3 deletions Source/Models/APIClient.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -5,23 +5,25 @@ import Result
public struct APIClient {
private let requestPerformer: RequestPerformer
private let deserializer: Deserializer
private let scheduler: Scheduler

public init(requestPerformer: RequestPerformer = NetworkRequestPerformer(), deserializer: Deserializer = JSONDeserializer()) {
public init(requestPerformer: RequestPerformer = NetworkRequestPerformer(), deserializer: Deserializer = JSONDeserializer(), scheduler: Scheduler = mainQueueScheduler) {
self.requestPerformer = requestPerformer
self.deserializer = deserializer
self.scheduler = scheduler
}
}

extension APIClient: Client {
public func performRequest<T: Request>(request: T, completionHandler: Result<T.ResponseObject, SwishError> -> Void) -> NSURLSessionDataTask {
return requestPerformer.performRequest(request.build()) { result in
return requestPerformer.performRequest(request.build()) { [schedule = scheduler] result in
let object = result
>>- self.validateResponse
>>- self.deserializer.deserialize
>>- T.ResponseParser.parse
>>- request.parse

onMain { completionHandler(object) }
schedule { completionHandler(object) }
}
}
}
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9 changes: 9 additions & 0 deletions Source/Models/Scheduler.swift
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
public typealias Scheduler = ((() -> Void) -> Void)

public let immediateScheduler: Scheduler = { completion in
completion()
}

public let mainQueueScheduler: Scheduler = { completion in
dispatch_async(dispatch_get_main_queue(), completion)
}
23 changes: 13 additions & 10 deletions Swish.xcodeproj/project.pbxproj
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,10 @@
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4A05CC291CEFBA4B0076955E /* Scheduler.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4A05CC271CEFBA460076955E /* Scheduler.swift */; };
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E51722F01CEE5D1A00B0C915 /* Deserializer.swift in Sources */ = {isa = PBXBuildFile; fileRef = E58AD6321C91049300AD2CDE /* Deserializer.swift */; };
Expand All @@ -37,7 +41,6 @@
E52E5DA61CE7AF2500023C91 /* NSError.swift in Sources */ = {isa = PBXBuildFile; fileRef = F8D09FB81BFD360A00FB2433 /* NSError.swift */; };
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E52E5DAC1CE7AF2500023C91 /* NetworkRequestPerformer.swift in Sources */ = {isa = PBXBuildFile; fileRef = F806950D1B962C5300C61B4A /* NetworkRequestPerformer.swift */; };
Expand All @@ -56,7 +59,6 @@
E52E5DD51CE7B36A00023C91 /* NSError.swift in Sources */ = {isa = PBXBuildFile; fileRef = F8D09FB81BFD360A00FB2433 /* NSError.swift */; };
E52E5DD61CE7B36A00023C91 /* NSURLRequest.swift in Sources */ = {isa = PBXBuildFile; fileRef = E5915B201BDABC4B005E5D63 /* NSURLRequest.swift */; };
E52E5DD71CE7B36A00023C91 /* Result.swift in Sources */ = {isa = PBXBuildFile; fileRef = F88ED0711B967C4A0069F56C /* Result.swift */; };
E52E5DD81CE7B36A00023C91 /* GCD.swift in Sources */ = {isa = PBXBuildFile; fileRef = F8D09FBB1BFD48F200FB2433 /* GCD.swift */; };
E52E5DD91CE7B36A00023C91 /* SwishError.swift in Sources */ = {isa = PBXBuildFile; fileRef = F8F59BB51C2B34B60020B5BE /* SwishError.swift */; };
E52E5DDA1CE7B36A00023C91 /* RequestMethod.swift in Sources */ = {isa = PBXBuildFile; fileRef = F867938B1BD29E37007D9E98 /* RequestMethod.swift */; };
E52E5DDB1CE7B36A00023C91 /* NetworkRequestPerformer.swift in Sources */ = {isa = PBXBuildFile; fileRef = F806950D1B962C5300C61B4A /* NetworkRequestPerformer.swift */; };
Expand Down Expand Up @@ -107,8 +109,6 @@
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F8DF3B881B964B20003177CD /* NetworkRequestPerformerSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = F8DF3B851B964B20003177CD /* NetworkRequestPerformerSpec.swift */; };
F8DF3B8B1B964B83003177CD /* Nimble.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = F8DF3B891B964B83003177CD /* Nimble.framework */; };
Expand Down Expand Up @@ -144,6 +144,7 @@
/* Begin PBXFileReference section */
2C721E401BD5A77700846414 /* Swish.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Swish.framework; sourceTree = BUILT_PRODUCTS_DIR; };
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4A05CC271CEFBA460076955E /* Scheduler.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Scheduler.swift; sourceTree = "<group>"; };
E506EC7D1BB5BE380032E941 /* NimbleMatchers.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NimbleMatchers.swift; sourceTree = "<group>"; };
E52E5D8F1CE7AE3400023C91 /* Swish.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Swish.framework; sourceTree = BUILT_PRODUCTS_DIR; };
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Expand Down Expand Up @@ -180,7 +181,6 @@
F8A00DE61BB5C86200169A46 /* RequestSpec.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = RequestSpec.swift; sourceTree = "<group>"; };
F8C39B501B969A71005E065F /* FakeDataTask.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FakeDataTask.swift; sourceTree = "<group>"; };
F8D09FB81BFD360A00FB2433 /* NSError.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NSError.swift; sourceTree = "<group>"; };
F8D09FBB1BFD48F200FB2433 /* GCD.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = GCD.swift; sourceTree = "<group>"; };
F8DF3B811B964B20003177CD /* FakeSession.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FakeSession.swift; sourceTree = "<group>"; };
F8DF3B831B964B20003177CD /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
F8DF3B851B964B20003177CD /* NetworkRequestPerformerSpec.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NetworkRequestPerformerSpec.swift; sourceTree = "<group>"; };
Expand Down Expand Up @@ -323,6 +323,7 @@
F806950D1B962C5300C61B4A /* NetworkRequestPerformer.swift */,
F8DF3B8D1B964BED003177CD /* HTTPResponse.swift */,
F88ED06C1B96736B0069F56C /* APIClient.swift */,
4A05CC271CEFBA460076955E /* Scheduler.swift */,
E58AD6361C91055200AD2CDE /* JSONDeserializer.swift */,
);
path = Models;
Expand Down Expand Up @@ -355,7 +356,6 @@
F8D09FB81BFD360A00FB2433 /* NSError.swift */,
E5915B201BDABC4B005E5D63 /* NSURLRequest.swift */,
F88ED0711B967C4A0069F56C /* Result.swift */,
F8D09FBB1BFD48F200FB2433 /* GCD.swift */,
);
path = Extensions;
sourceTree = "<group>";
Expand Down Expand Up @@ -698,6 +698,7 @@
E51722F01CEE5D1A00B0C915 /* Deserializer.swift in Sources */,
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4A05CC291CEFBA4B0076955E /* Scheduler.swift in Sources */,
2C721E5D1BD5A7E800846414 /* APIClient.swift in Sources */,
2C721E591BD5A7C500846414 /* Client.swift in Sources */,
E5915B221BDABC4B005E5D63 /* NSURLRequest.swift in Sources */,
Expand All @@ -706,7 +707,6 @@
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2C721E5B1BD5A7D400846414 /* Request.swift in Sources */,
2C721E5A1BD5A7D400846414 /* RequestPerformer.swift in Sources */,
F8A7CADC1BFD5EBD008B9224 /* NSError.swift in Sources */,
Expand Down Expand Up @@ -736,7 +736,7 @@
E52E5DA61CE7AF2500023C91 /* NSError.swift in Sources */,
E52E5DA71CE7AF2500023C91 /* NSURLRequest.swift in Sources */,
E52E5DA81CE7AF2500023C91 /* Result.swift in Sources */,
E52E5DA91CE7AF2500023C91 /* GCD.swift in Sources */,
4A05CC2A1CEFBA4C0076955E /* Scheduler.swift in Sources */,
E52E5DAA1CE7AF2500023C91 /* SwishError.swift in Sources */,
E52E5DAB1CE7AF2500023C91 /* RequestMethod.swift in Sources */,
E52E5DAC1CE7AF2500023C91 /* NetworkRequestPerformer.swift in Sources */,
Expand Down Expand Up @@ -774,7 +774,7 @@
E52E5DD51CE7B36A00023C91 /* NSError.swift in Sources */,
E52E5DD61CE7B36A00023C91 /* NSURLRequest.swift in Sources */,
E52E5DD71CE7B36A00023C91 /* Result.swift in Sources */,
E52E5DD81CE7B36A00023C91 /* GCD.swift in Sources */,
4A05CC2B1CEFBA4C0076955E /* Scheduler.swift in Sources */,
E52E5DD91CE7B36A00023C91 /* SwishError.swift in Sources */,
E52E5DDA1CE7B36A00023C91 /* RequestMethod.swift in Sources */,
E52E5DDB1CE7B36A00023C91 /* NetworkRequestPerformer.swift in Sources */,
Expand All @@ -796,6 +796,7 @@
F867938C1BD29E37007D9E98 /* RequestMethod.swift in Sources */,
F88EE3141B976747001EEB44 /* Result.swift in Sources */,
E5D7E0A11BBF2021002A3738 /* Client.swift in Sources */,
4A05CC281CEFBA460076955E /* Scheduler.swift in Sources */,
F8DF3B8E1B964BED003177CD /* HTTPResponse.swift in Sources */,
E58AD6371C91055200AD2CDE /* JSONDeserializer.swift in Sources */,
E58AD6351C91053000AD2CDE /* Parser.swift in Sources */,
Expand All @@ -804,7 +805,6 @@
F80695141B962C5300C61B4A /* RequestPerformer.swift in Sources */,
F88ED06D1B96736B0069F56C /* APIClient.swift in Sources */,
F8F59BB61C2B34B60020B5BE /* SwishError.swift in Sources */,
F8D09FBC1BFD48F200FB2433 /* GCD.swift in Sources */,
E5915B211BDABC4B005E5D63 /* NSURLRequest.swift in Sources */,
F80695131B962C5300C61B4A /* NetworkRequestPerformer.swift in Sources */,
F8D09FB91BFD360A00FB2433 /* NSError.swift in Sources */,
Expand Down Expand Up @@ -1229,6 +1229,7 @@
E52E5DA11CE7AE3400023C91 /* Release */,
);
defaultConfigurationIsVisible = 0;
defaultConfigurationName = Release;
};
E52E5DA51CE7AE3400023C91 /* Build configuration list for PBXNativeTarget "Swish-tvOSTests" */ = {
isa = XCConfigurationList;
Expand All @@ -1237,6 +1238,7 @@
E52E5DA31CE7AE3400023C91 /* Release */,
);
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defaultConfigurationName = Release;
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E52E5DD11CE7B2BA00023C91 /* Build configuration list for PBXNativeTarget "Swish-watchOS" */ = {
isa = XCConfigurationList;
Expand All @@ -1245,6 +1247,7 @@
E52E5DD31CE7B2BA00023C91 /* Release */,
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F80694EB1B962BB900C61B4A /* Build configuration list for PBXProject "Swish" */ = {
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Expand Down
18 changes: 14 additions & 4 deletions Tests/Fakes/FakeRequestPerformer.swift
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,11 +24,13 @@ extension ResponseData {
class FakeRequestPerformer: RequestPerformer {
let statusCode: Int
let data: NSData?
let background: Bool
var passedRequest: NSURLRequest?

init(responseData: ResponseData, statusCode: Int = 200) {
init(responseData: ResponseData, statusCode: Int = 200, background: Bool = false) {
self.data = responseData.data
self.statusCode = statusCode
self.background = background
}

func performRequest(request: NSURLRequest, completionHandler: Result<HTTPResponse, SwishError> -> Void) -> NSURLSessionDataTask {
Expand All @@ -38,9 +40,17 @@ class FakeRequestPerformer: RequestPerformer {
NSHTTPURLResponse(URL: $0, statusCode: statusCode, HTTPVersion: .None, headerFields: .None)
}

completionHandler(
.Success(HTTPResponse(data: data, response: response))
)
let complete = { [data] in
completionHandler(
.Success(HTTPResponse(data: data, response: response))
)
}

if background {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), complete)
} else {
complete()
}

return NSURLSessionDataTask()
}
Expand Down
45 changes: 45 additions & 0 deletions Tests/Tests/APIClientSpec.swift
View file
Original file line number Diff line number Diff line change
Expand Up @@ -191,6 +191,51 @@ class APIClientSpec: QuickSpec {
expect(error).toEventually(equal(SwishError.ServerError(code: expectedCode, data: performer.data)))
}
}

describe("scheduling completion blocks") {
it("dispatches onto the main queue by default") {
let performer = FakeRequestPerformer(responseData: .JSON([:]))
let client = APIClient(requestPerformer: performer)

var isOnMain: Bool?
client.performRequest(FakeRequest()) { _ in
isOnMain = NSThread.isMainThread()
}

expect(isOnMain).toEventually(beTrue())
}

it("doesn't dispatch onto main queue when using the immediate scheduler") {
let performer = FakeRequestPerformer(responseData: .JSON([:]), background: true)
let client = APIClient(requestPerformer: performer, scheduler: immediateScheduler)

var isOnMain: Bool?
client.performRequest(FakeRequest()) { _ in
isOnMain = NSThread.isMainThread()
}

expect(isOnMain).toEventually(beFalse())
}

it("dispatches via a custom scheduler if set") {
var calledNoopScheduler = false
var completed = false

let noopScheduler: Scheduler = { _ in
calledNoopScheduler = true
}

let performer = FakeRequestPerformer(responseData: .JSON([:]), background: false)
let client = APIClient(requestPerformer: performer, scheduler: noopScheduler)

client.performRequest(FakeRequest()) { _ in
completed = true
}

expect(calledNoopScheduler) == true
expect(completed) == false
}
}
}
}
}

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