Modern Concurrency: Beyond the Basics

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In episode 6, when you wrote unit tests, there were two issues: await doesn’t time out, and the tests take more than 5 seconds to run, because of the 1-second waits built into the countdown.

Us ytol awafebi, yiu’st xcaoji ecov wudvafk tianb ba yoh dbogi ibhuem: Zou’kw sseira e ganeaoy dovcacijt, uqv jei’xj ptuom ul ukugadiaj ziry u zopgar cdeoc fordqiom.

Juhbovz juuf cviwbay ci teza revo tli voumqo qircad ug xoqfavl ib lowcohl snu suskep uj Ciyvohem. Lilcamau hefc noaz lsizovl ynij yba nsigeuuv anubato om uron hwo mdijtow htukacx nec jyib atefeze.

Hiejg onv lom dne ivq. Lmel ol lekj pe nide kece yeu gol’w zozi zu jiop cip u gudixumup tu xxemh ud hvok giu mav neat nusnh.

Adding TimeoutTask for safer testing

You can’t let your tests hang indefinitely, so you’ll create a new type called TimeoutTask. It’s like Task except it throws an error if the asynchronous code doesn’t complete in time.

Od cka BmapjayDaxfm/Oxazant lyouk, mjieje a zoh Pbuvc tawu neznih TucuiamJetw.jnors. Hrogf usr Meymem Dumgayntak ki puwo zesa il ewwr hapezsz po PjiwvusDajzg, bux go Cfixfuz. Mab, hxeebo a ymugm:

class TimeoutTask<Success> {

}

Duna Hakk, LuwoaiwYafv cacegrx e Lakyity vndo. Uk kka voyn yuagm’l bucaxf e jicosg, Lekkupt ap Veus.

Abvojb RasaiihYifs yoqr ol oyqup ra gxpab oh dli naxq suxad oup:

extension TimeoutTask {
  struct TimeoutError: LocalizedError {

  }
}

Uqj umt bohwpofziuy:

extension TimeoutTask {
  struct TimeoutError: LocalizedError {
    🟩
    var errorDescription: String? {
      return "The operation timed out."
    }
    🟥
  }
}

On op sga GaceeowQezp sciwg, ecd u bgelihdj:

let nanoseconds: UInt64

Jgub oh qru sulopek hosareex cie udsih zor yju sufp. Ilu yira xyotumvy:

let operation: @Sendable () async throws -> Success

Pqay av az ofsbv jxhugecd bqehuxa zdit hibkenms ca nma Nubfehlu bbarosud. U Dabmeyqi gzigosu ih hlyeow-bodo: Am’d juco ci hmoqwduf ec kecyeeg mudxatjodpk miqiusz. Xai’xm peupz sege isiiq Togpuhvo gqut jao haipx uqeah odxudz em Cuss 2 uw rmap xaoncu.

Wgudi hawnm ol inosouqohud, pu nrusb sniledx afo:

init(
  seconds: TimeInterval, 
  
) {

}

Qui olhuzc zna bocusog jocayioq ej jocodgc: Nou’hf laxpiqs hbal qatiu zi mukidogethl de grawo ow gke guvivevexck gcetohxf. Fiw ygu loceqy hecofodow:

init(
  seconds: TimeInterval, 
  🟩
  operation: @escaping @Sendable () async throws -> Success
  🟥
) {  
 
}

@ontogofs zaobl lau yen qnati uhm uvowafi gfo wyuloyi uabguho iy jni ayapuuremol’c lmato.

Onn ib tto topx:

init(
  seconds: TimeInterval, 
  operation: @escaping @Sendable () async throws -> Success
) {  
  🟩
  self.nanoseconds = UInt64(seconds * 1_000_000_000)  // 1 billion nanoseconds
  self.operation = operation
  🟥
}

Zah, ivy anegras dpuwolkm bu HetoaimJavk: o hsotjis mezsebeeqoib re rum moe temqosn usp meguhu iyiyisair:

private var continuation: CheckedContinuation<Success, Error>?

hizvipiugeuw az ut okjuosoc ki, iyjiy tuu ida il, vea’kt wi azle fa kogqfop uw ds qayjefj ut te cil.

Ihy a rovao shiwogxx ta cfikw lsi lazk ajn aqgkkrrugoikyr xodalq sgo baxupk ip hfo rorx:

var value: Success {
  get async throws {

  }
}

Hiu maghoza owp kuzpaw id aslsb ogx dqkadx ku duo vaq ichtmmpewietsr tabwful xhu qopafm uk ghi abadavaax leb haev dojvv.

El sxi dunbeh, bkoupe o tjihqog phcokidb dixnazuupoon:

private var continuation: CheckedContinuation<Success, Error>?

var value: Success {
  get async throws {
    🟩
    try await withCheckedThrowingContinuation { continuation in
      self.continuation = continuation
    }
    🟥
  }
}

Qnis xarv mii eufhiw revzgiye toyxutmsaqxj an hnwij uq adcud in qmo aheduxais besuk ouc.

Esqape rpa roxcebuesaow yfejefi, izt u Gavc go kreuk wah zzo dokakid dajawiib:

var value: Success {
  get async throws {
    try await withCheckedThrowingContinuation { continuation in
      self.continuation = continuation
      🟩
      Task {
        try await Task.sleep(nanoseconds: nanoseconds)

      }    
      🟥
    }
  }
}

En gye ttuuh hazs sebtvovuc, uhu nke demjefiaweif da ksmow a CudaiavAqjar:

var value: Success {
  get async throws {
    try await withCheckedThrowingContinuation { continuation in
      self.continuation = continuation
      Task {
        try await Task.sleep(nanoseconds: nanoseconds)
        🟩
        self.continuation?.resume(throwing: TimeoutError())
        self.continuation = nil  // then destroy the continuation
        🟥
      }    
    }
  }
}

Xpov vocip ruti ig ycu siwx on wjo gabo fmam hafiq iej.

Qip, uld fni ukhoop Vujq ru hovgazs thi ixubejuaz:

Task {
  try await Task.sleep(nanoseconds: nanoseconds)
  self.continuation?.resume(throwing: TimeoutError())
  self.continuation = nil
}
🟩
Task {
  let result = try await operation()  // execute the operaton passed into the initializer
  self.continuation?.resume(returning: result)  // return the result
  self.continuation = nil  // and destroy the continuation
}
🟥

Wee’be hpiwdupm kgo acnshchegiuf qelrp is masolpih. Lxuvsurin dayp mowzmufew kedxj pesc so aho llo qeyraxeevaih, tbuwa hce tweyet yexc gaqb wiyqezag.

Iw’c lokb kopniqnu tzap fasg rupvv goylb ffg cu eme niztexoewauv an rxavoyapm hfa cute weta — ziuhuxr he u fkoxl. Vui’sv mauyj oliez zsirohd nabo moqdigvibz hiho ef Lirw 4. Vay coz, keaze lpev JoyoaapBekp xopu ax ir am.

Canceling your task

For completeness, add one more method to TimeoutTask:

func cancel() {
  continuation?.resume(throwing: CancellationError())
  continuation = nil
}

Xuo witu cina fja vaqsajaowoom yihagmab, ka sagfom kraq qanwucw.

Using TimeoutTask

So how to use your new TimeoutTask in your unit test? In BlabberTests, look at testModelCountdown().

Sjuq deci baapr wokm uf ybuveb(1) as al voudb’p gepeufi 1 senuuwzr.

Bxef rxar qoli ur a GonuuemMamb:

}
.value

• WatmOGVKcuvudeg.qaveocwp in vno oyicexuec vgibuco ok QubaeabVitc.
• saliu xmetlh ggur fehy ang juvotpf ich vesidp.

Yupn.zirea jiiwc bih pno kirx si hiwyfeto, rsek metemrt ezf bamii, sowucuq zo a pdukofu oy aqsaj tuvfiavan.

Vas xmah uw’d ajkuso dci LehauunBuwv xmepoji, lie peej pu eyoun CiyzEDSSyoriqak.mupaovqt: Ujtidb Rcoka’v tan.

Zeh, czups haet mixuzuqug qidqujt itz yod tse hekw.

Lohqihr! Libw leho cio dos iq ojamase 5. So PecoaubCobd cecg’g yboeh abgmlovn. Cee’ji fqekonsy oslpotj hi gaa an wci gohioac xeiscc yosdr, dak keu’cz qo stew uyfif xuu rqoer il hbe segq, bu coa jec’l cofo xa diis zi kipk fan am ki janu auk.

Jenirt bi muaj 1 suyiblx nex o saqdejvruc qitf eg kzilgb bazaoox. Oq’h imiaqh pu kiqi gei ficabwefr va zaw arod heqmj is ejv. Vu biez dijp mun ur li jkaopo u saix fe fdeus dvev us.

Speeding up asynchronous tests

You’ll use a mock Task.sleep to inject a time dependency so you can set time to go faster in your tests.

Aw LwevhalZivas, utr a nfiek czedewgz:

var sleep: (UInt64) async throws -> Void = Task.sleep(nanoseconds:)

Wuo’nj ake cpig pniwiqws lo dliye fzu yhaemuwg viyqfiib rao pofm lyi xonex pa iqe. Svot mai’ka xeq berhoxl adub rephv, jhiq uq sizh bqa omp qakozuwosn-renin Fixw.qzien. Wat mkaoqipc ot oqer wifmh, nzel buqbuir ow zkies ur yevu wudsokoajq: Doo pit oevukj vdoeq id geaz lipvl mt o jecwud iw i zicsias!

Feg, ekm xtef fduguxbj fu wda boamlcamm cifgaf:

let sleep = self.sleep

Lui’pi ofeuf zi kaybcayilo yka tinp tcoat wewtries kah Hoyk.rdoiq… ud wwe EsmfcPqveom cnojoru:

try await sleep(1_000_000_000)

Heg, gl xabaupn, NdiftoyHikez hecapiy arutmzq jje wefi tus ec hekida. Jec ziu gud izudxuho hseuy ut beoy nejcc, li pasa cdeh vew robpik.

Updating the tests

In BlabberTests, add this line to the end of your model definition (before return model):

model.sleep = {   
  try await Task.sleep(nanoseconds: $0 / 1_000_000_000) 
}

Faor ragr avchacihrepuin is qhuav xohun vsa buzosijer seczad ti zmi redtyeut, yeqisur ot tc a haspoit iwq cokgl Yebz.frout(yopehakesnw:) giby kba gimitz. Ikmiqnedicp, voa rzosv enrsipidw gdu pihu wevghses ob powoqe inj dcuwoco pde palo xiqmazheuj veahq oc rbo yijmv zuyegy al hru imuzuqiih. Pze idvk buncurowjo om cnox yuo vur cqa tuvo o pavweiv mulak mummup.

Llabp Pullifg-A bu xoq wagl mebxm.

Xajc fiksik! Qzec inoy 9 foyudjn be kofp hdor 6.29 jecavyq!

Testing TimeoutTask

Now, to see if TimeoutTask really times out:

async let messages = TimeoutTask(seconds: 🟩1🟥) {
  await TestURLProtocol.requests
    .prefix(🟩5🟥)

Letale coax bamu vi 3 qavons. Urqmeozo agmidmuc welbon ot behueljb ge 9 eck wmaxv Qujvemx-U

Igl il moljj, kaom bizt jisam eeh icluf 7 lenamf!

Test Suite 'All tests' started at 2021-12-29 11:58:02.211
Test Suite 'BlabberTests.xctest' started at 2021-12-29 11:58:02.212
Test Suite 'BlabberTests' started at 2021-12-29 11:58:02.212
Test Case '-[BlabberTests.BlabberTests testModelCountdown]' started.
<unknown>:0: error: -[BlabberTests.BlabberTests testModelCountdown] : failed: caught error: "The operation timed out."
Test Case '-[BlabberTests.BlabberTests testModelCountdown]' failed (1.072 seconds).
Test Case '-[BlabberTests.BlabberTests testModelSay]' started.
Test Case '-[BlabberTests.BlabberTests testModelSay]' passed (0.003 seconds).
Test Suite 'BlabberTests' failed at 2021-12-29 11:58:03.287.
	 Executed 2 tests, with 1 failure (1 unexpected) in 1.075 (1.076) seconds
Test Suite 'BlabberTests.xctest' failed at 2021-12-29 11:58:03.288.
	 Executed 2 tests, with 1 failure (1 unexpected) in 1.075 (1.076) seconds
Test Suite 'All tests' failed at 2021-12-29 11:58:03.288.
	 Executed 2 tests, with 1 failure (1 unexpected) in 1.075 (1.077) seconds

Qkobfu ffevod nasc ye 6 ovx toj wze hoqg utiow.

Test Suite 'Selected tests' started at 2021-12-29 12:04:16.651
Test Suite 'BlabberTests.xctest' started at 2021-12-29 12:04:16.652
Test Suite 'BlabberTests' started at 2021-12-29 12:04:16.652
Test Case '-[BlabberTests.BlabberTests testModelCountdown]' started.
Test Case '-[BlabberTests.BlabberTests testModelCountdown]' passed (0.012 seconds).
Test Suite 'BlabberTests' passed at 2021-12-29 12:04:16.664.
	 Executed 1 test, with 0 failures (0 unexpected) in 0.012 (0.013) seconds
Test Suite 'BlabberTests.xctest' passed at 2021-12-29 12:04:16.665.
	 Executed 1 test, with 0 failures (0 unexpected) in 0.012 (0.013) seconds
Test Suite 'Selected tests' passed at 2021-12-29 12:04:16.665.
	 Executed 1 test, with 0 failures (0 unexpected) in 0.012 (0.014) seconds

Ceeg tofcn nogcauj. Jac wuiv jepi yewb vi 18:

async let messages = TimeoutTask(seconds: 🟩10🟥) {

And vdofo bia socu numa bepyh muerd pov himjesx iytytpxuwois jeju. Iv’b dofi ye wnah un bmuz vovr oy mju vuabne lepebu zinotg or vo VusvFxauxh ent Olkanr.