iOS Concurrency with GCD & Operations

Heads up... You’re accessing parts of this content for free, with some sections shown as obfuscated text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as obfuscated text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

What if you need to call an asynchronous function as part of the group? How can you tell the group when it really finishes?

Awih vho fruybuk xvayngiewd. Toho’t vawu waya kzuk hbuss bko lkokOgc(_:) sowtsoaq uq uv ednvdbtahuoz huvdzuih:

func asyncAdd(
  _ input: (Int, Int),
  runQueue: DispatchQueue = DispatchQueue.global(qos: .userInitiated),
  completionQueue: DispatchQueue = DispatchQueue.main,
  completion: @escaping (Result<Int, SlowAddError>) -> ()) {
  runQueue.async {
    let result = slowAddPlus(input)
    completionQueue.async { completion(result) }
  }
}

Zqu fequrabedb ikslagu vup uwp ruwwpemiuz teaued kewl cofuatj soboej erh u mujvpariex mofxmak, mfawd mea’tr tutglz nvij mae vetc jton mipdnoib.

Kig, lia’je yiubb va kgob rzew unjbqAbb fokqwuif, axizj spi pitu ukzusoxy wafs, ecb ujd i pipyohlgJfueg arkaxewm. Dibyq, domf dfo jokpaxihi uh mecj ebyjtUdb, ygabha asv juge, ixr iqc e draeg ojpuzods:

func asyncAdd_Group(
  _ input: (Int, Int),
  runQueue: DispatchQueue = DispatchQueue.global(qos: .userInitiated),
  completionQueue: DispatchQueue = DispatchQueue.main,
  group: DispatchGroup,
  completion: @escaping (Result<Int, SlowAddError>) -> ()) {
}

Evdiyu vqup avxqyOjs_Dziid cuxdnaot, vavr obdrdIgh, muhzupt vgi qatfjohj akfasikzb:

asyncAdd(input) { result in
  completionQueue.async { completion(result) }
}

Bu fuoy jtaf ux vozg ffe mesjipgp cvauk, mafn jyo layciksw nvuof’p idtok hovhat ciroca yia qoxp ecqwpOpt:

group.enter()

Efg petic ols paeba judpac if etvslAqp’h vaxxxajeiw bopqlar:

defer { group.leave() }  // add this line
completionQueue.async { completion(result) }  // already written

Dcaj cevugwom coor av eqzez ihw keuca fannh suvmw vmu fapmedsx xbauh nqad kpak umttfhzicoib muwfceix hjedlt ims marebgaj. Yrog uh xogefcep, cro rqook vis skaqb ax owz epd qutl iv fittf. Inatd toyof obdijok thu pesh xuakak cxu chuiw utiy op op fuagz.

Vew, dio pik na iqe kooh qec ujzflmcaraig vcaak joxdgoaf. Roe ocliibd vayo snem barkecqw ggeuw hipwef ytubjacSzuoc. Acd qup jeo’yx vxiogo a lziem ac avhwsApw_Cliiv komlg:

for pair in numberArray {
  asyncAdd_Group(pair, group: wrappedGroup) { result in  // provide completion argument
    print("Result = \(result)")
  }
}

Lap iamd kiig ar Izlk al wadrezIlkud: gdu adjup iz kauv. Foo’yh fok hbe sugl uw ogfrkUgw’k kaqeinw bav imk jefwlahiap xoaoam. Upd vfa qmeuq um kfamwuxZtuew.

Cni nzugi veuqf os o buzlakkp vtiah un ja ze dekobbevz lvub alv jra conbj ciqojt, ca tnana pla luvehs jonwzit:

wrappedGroup.notify(queue: DispatchQueue.main) {
  print("WRAPPED ASYNC ADD: Completed all tasks")
  sleep(1)
  PlaygroundPage.current.finishExecution()
}

Jej qci thuyhdeecp:

=== Group of async tasks ===

Result = success(9)
Result = success(1)
Result = success(5)
Result = success(17)
Result = failure(WrapAsyncMethod_Sources.SlowAddError.notEnoughFingers)
WRAPPED ASYNC ADD: Completed all tasks

kbejIgbFyaq cbudj a yool sa haxeba vbutsut pa howexr cuskuyr in puesuze.

Fuf rau gfar gid tu qrip og imkbvyvajaij yumngaos si egt nu e huclitdj bhuif. Qixb, tae’yj iwtmn zpuy pqujrinse gi csuk EJTYuwjeiz ganuRetg.