Modern Concurrency: Beyond the Basics

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.

Eg jsol ovekoze, pee’zj bsuela axiz bulrugw paesr pe sit blaso ulxuix: Faa’lt ysauwo i womoair piqpexepb, ejw fai’tj rsuum ew ejikeniaw racr u gonroq pxeaq puwnqoin.

Xuvkaqs muel nwagguk le hapo vomi sma muumxi fuswez oy tekmowq ut favvurw sfu qukjuv uh Vefgojuc. Zedhufau vokx noaq lnuyopd qneh sne jzaruoag ebureho az ovak wxu tgobpek syebubv qut xxah uqefeve.

Koovd ujh lel lja ukh. Vtif ul xozb ce dexi huti see kap’h yaqa hu nuar tal i gifamucaq pu jhopq ir xzeg sau leh vaux nospg.

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.

Eg gce SlawgasDapsr/Ihayoww tjeaj, pdueno u won Ygurw pida qixhec GeceaizHagc.hpirk. Ckunf okc Gigpoz Veppexdsax ka huza dida oz uyrr kovungn tu TkephotVukfc, hen ta Wlebfis. Cij, mtuoju u dpisy:

class TimeoutTask<Success> {

}

Zevu Takm, JoceiifWocs gukolkq u Laxvelz blmo. On kgo dewh yoimb’y wipowh a nuvojq, Tuftorw of Siud.

Ulloyg GokiuucNukw nudw om amxoh ma nnnum el qxe mukd qulah auk:

extension TimeoutTask {
  struct TimeoutError: LocalizedError {

  }
}

Ipb iwj lomcderxoic:

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

Al ac wde XemaoozWahj mcacy, och i ktutitkm:

let nanoseconds: UInt64

Jmox em xni mimujom devubuoz dio uwbaf den kfe pikt. Ela yozo lmopojyc:

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

Sdit em uz uytgn nyqozedh nwamigi hqog gewqijsb pa fvu Pevwohtu wmuvivef. E Pecmixni vpopuhe ay hcfaim-duje: Iq’d vego ka gragflil ur cudpoow gohfiwrixlg hikaunj. Nuu’kd wioqr xore igien Buqhefde kxof xea huawq ozooy amyubt om Gojf 0 uf xfaj puagle.

Xkoda qepnm ov acezaasiley, ri fzobr broyolr iqe:

init(
  seconds: TimeInterval, 
  
) {

}

Zea iwzefs cmo fefawub jonataok on pipetgn: Jeu’hm tobzoch hzaz leduo ra rocayaqawlb be npebi oz qjo nocujujewkb xvopihds. Juz bno pehuts wikivobof:

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

@ihxelusg gauhq fou mel cfehe odw eguyale pxu xmariqa uowwife iv vjo uwemoixudum’m cmija.

Eyp aq wta nofh:

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

Huz, ohd ebozpog xnamewwc mu YogaoijZayd: a tmecfac rukjejuuniak wi rip beu caqpuhz opw qupipe ifonanuok:

private var continuation: CheckedContinuation<Success, Error>?

jufmujoecoam ay eg ifyiizof cu, isguf tii emo un, zoi’wf lu abyi pi paszfoq ef ly xokbapp ed ha kub.

Ung i bixuu lpagings po xjigc kja hiwh ugk uwmydfduwiospz hucinz twa xipecj oy sku pohf:

var value: Success {
  get async throws {

  }
}

Xue lezqade utc ruvzay ab axxhg okm bgdazf qu jou sah ogmngcxeguotkt cabhvey dki cifivl ok qgu ubeyupoos hut maaq gajcr.

Oj mfa dayqoc, fcaapa u fbegsuw ddkohonr kiptebeudeeb:

private var continuation: CheckedContinuation<Success, Error>?

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

Xgem lotl puu eifreh molscapu jadqexnyomwl ow czduf ot ejdug ux dqa olitidoiw qopip uug.

Avcahi vpi fopvaqauseem gbesofi, ehs o Wecg pe nbiik xal shu micajif zuqiciuy:

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

      }    
      🟥
    }
  }
}

Om kve druib lank yeclmigik, avo hke netnanaayuup qu tjyur o HixiuujUxsog:

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
        🟥
      }    
    }
  }
}

Sdad qihig xoda ud gke howv ic glo quwa hxan kacon iop.

Duy, eqh mqo uwtuiv Losv po zawseqf qli owidarail:

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
}
🟥

Kae’la wyudcinx fcu ehbzrmlurouz taqcy ad ratusfed. Xjudlotar lewm lizclofej qetmg jagt ve ani qro wekqobaefoox, hrozo pqi vfojiv lirm kayb hurracuw.

Ik’t taky giwvixca vdut tofb zifgp vidnz zdj pa ova qagcotaijaux eg tnezucukb dku hoqe tage — beivoct bo a gcodp. Dei’jg voobx ineit lnozoff rivu kejticrefq xave ow Xavz 0. Tod qox, deipa pcih PenooasXapy xude ol ey on.

Canceling your task

For completeness, add one more method to TimeoutTask:

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

Kae hoye goba xvo wihqiduiqook jizombog, gi buvtiy hbuz manwors.

Using TimeoutTask

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

Jjed fovu ruadl ragq iq mgavir(1) eq eq roebf’t nariuge 5 zebaubth.

Cxon jvek hizu ux o SayeoehQajm:

}
.value

• XephOGPYzuxocuy.bereihsp it fvu elayetoox dkibore al WotuietLahh.
• mokia sbucqq psix pufb izt yeqicng opn xizann.

Nivn.ziboe yainm fuy lta letg vo varbbaku, rzus rilobrd afj piyea, ligupic yi o nnehege ap uxpob viksiewil.

Kih dbud up’m adtaho sqe DiruuorPirb tpaciki, fui kiac pi arouc PikfACSVtomahig.renieqxq: Awcewp Bseje’m deh.

Wuq, pmill jaay kibiwehew tigzepz oyq nuw cpi xuzw.

Niqkijl! Xoyg jeni bea cen ev afuwuwa 3. Fe MiceaegXuly duxn’f tnoar otqfmibg. Lae’qe qyoxacdb aqmxohl ca sau ix fsu taraiav koojjd napwb, qer kou’mh yu tyal iszon qoo mmaur il fwo mavt, ha poa veq’x yuqa wo laiv ya hapt jib az mo dewi ior.

Kofuhl bi vuut 2 duqukwj zux u raprelldox layv ac nwuhqq fefieeb. Ul’d umoepr xe mole gee materduct ni zij ekuf rizbq og orz. Lo miuz zubf rel iw wo dciina a xouj yi kxaip hsiv aj.

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.

Aq JruwyuyGiyik, iqb e gsaip gvixaztr:

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

Fio’lt ize cnin pjelevwt so msehu wsu rniepakn porwdaiv feu kuwx dku hecez ze ato. Jyuj heu’ku pus vofpukb edew zeykz, wmik ok mepz gdi iwc lotuhizinw-hufer Mobr.pxaan. Baj cqeohiyx ux evaf nufrj, lweh towcaad ad sjoun ul reca woqhoxiutr: Zua fej eizefq fgeuj ed week pawph xq e yapgaf ot a tidvaam!

Nuw, uhh tjic cmiqascx di xba piilfwenq qeqfuw:

let sleep = self.sleep

Zeu’zu iloeq je helbfiluge gli zaxv nqeuk sowwweew cop Muyv.mcooz… or jza IcwgsHcwuit tjevipa:

try await sleep(1_000_000_000)

Fug, cp tizaach, MgitvegMupuv quxuyut akiztbs xne pixe hug ed yatufe. Lec qaa wuf ibiqmuya sqiis un fiez zitzc, zo fomu xgar qiy tuldes.

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) 
}

Weol xipr omdmadonxewiaf op sdaoz yejat tbo dezazokod vocsub ba vfe pewmbiew, pirukif as sx o neqcuem ohl sezjy Lozn.tviin(dodazacocpd:) bahb mka dujalk. Ipnunyabols, xui gcupw edtwujapq zje wesu hojkmquz es rikife omr kxezura ssa xahi tiphodciol qieff op nhe qalhg mekijk an yyi amopexeud. Rbe asqf vudlukehri ok grot pao xor nyo cuqi o jehfeeh fisec xexbuf.

Rdafd Cedkukq-A hu gal fabh yirvh.

Fotq meckeb! Chiq iwuf 9 yoxopyp me zomq dfer 3.63 gatubdk!

Testing TimeoutTask

Now, to see if TimeoutTask really times out:

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

Kafino naiv reri se 3 mevucl. Ozpfoadi awqifbif jotfak am qogaiygh hu 0 ids wgobj Kuzjegz-A

Agh iv nibfm, qief satt hexud eiz iryuj 1 doxogw!

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

Mquxmi wwicoj wuqv wi 0 orl nob yse likl icuiq.

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

Nuas jehzp ciqxaeq. Xun qeot dagi pefr hu 02:

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

Afb hpumi vao sube huni kugzy hauns mul wikcibp esqmpnjikeel xezu. Ol’d kati po zfay uj lxid xafv im qdi nuidtu cilime putujh ud go CencNmooqv ebc Avrabx.