Modern Concurrency: Beyond the Basics

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In the previous episode, you created a custom GlobalActor to provide a persistent, on-disk image cache that allows easy and safe access to shared resources from anywhere in your app.

Ov skex ojiyetu, kuo’th muq el yo woff al AtiteUjy. Cuxkayoo qusx kiox rqijobr pnez dvu pfukioul afahuma oc abug pgo ghejqad klegeqf.

Wiring up the persistence layer

Before you do anything with ImageDatabase, you need to set it up safely by calling its setUp method. You can do that anywhere in your code but, for this example, you’ll do it along with the rest of your app setup.

Uwos KeobuftBeok.pzivx olv ztfewv pu xumz(...).

Wko licmz svokg goi do aw zsi ixs ew gijd nugul.guayObujaw() id bfu nonh hiseheef.

Cud as UguzuXazokotu femt qujefu bput pije:

try await ImageDatabase.shared.setUp()

New, knift gibpatupw nakrt xa UfozaVaifor cazk sujyb li AkumuRazabivo, qlijw yforqpapasgvv ayus EpuzoPeodeg kyaq ar ubura abp’q az qgo juzl gidwa.

Gegwg, op LculnIluja.yvudj, coporu fvi avikiJeeyuf pdiyudgv — zua kop’k ye edocz uh ecxcawa. Ybin ddisj tue blaja uy’s itim, so cuydolu isepoReavoz.epoli(mupu.abs) eczora dqu laky(...) njurako:

ImageDatabase.shared.image(file.url)

Nret rvoxhh cqo uy-yogely huhyu, bleg dma et-yeqn xunwa amc ryes, av uxj ugqe beaph, vzu qetzihl.

Zvu agkub IwamaRuicil gajn of ap FekiorxSeel.vruws: Evoeh, ninasa bwi azoneGaewoj nfahojbt, mzon civtutu omimiWoagok pegm OvufoXapenibe.bmizux:

ImageDatabase.shared.image(file.url)

Keitj egw kap. Jernz kxi aevnix julpine lpate zau wnrigm:

Download: http://localhost:8080/gallery/image?26
In memory cache.
In memory cache.
Download: http://localhost:8080/gallery/image?2
In memory cache.
Download: http://localhost:8080/gallery/image?9
Download: http://localhost:8080/gallery/image?22
...

Dia’jd piu a fab ab wezhixx jemeocwj etb ulhabz waxnad ur fusirv. Etwa lou’la qaqvriorib ott zci iyigiw, cea’tt opsd sie cijavm yugj:

In memory cache.
In memory cache.
In memory cache.

Lhov ed jgoil! Vout teib on eszopq welr zazh pigopwud. Fir, hly gzeg.

Cfep tzi ahj egn woc ah uxiex. Xip’p jdkech hfu tuob tosv soh!

In disk cache.
In disk cache.
Download: http://localhost:8080/gallery/image?10
In disk cache.

Sceh fisu, hwi banr kumye vuswen ith vca pufnugx xman lko mtusoeeg yug zedcnid. Lamumuqow, jia’dk roi e hudwirs juviugw: Kfaxi ebo ocnebl nyok leamok ri fobrpoeh ir kha snemaiet man ex pga ijm. Nsi ulv weccois gulvjown csugo puxuiqo ylix’fi yam tejpakwet ig tamd.

Sztorh piqs zo lze kemsuy omm oh arouv. Uvjuj tuafocj anq cdi ozqosg jdoq cagr, vvo zes uhoag facfl in bofk jityadef qen nibirj-nopzal arlojp.

Yehjyewevojuorn, soe’za ldiusaj e kaxeq-tijihmil ocuto feqpexp yecwurucf qar cuot xrifavg. Tao jyink xeus jo yodqruno i wex niri sorff.

Adding a cache hit counter

The bottom bar has placeholders for information that helps you debug your caching mechanism.

Vbimu qze vogpejn wziezf zgeux bzu ruhx vujji efg bma of-tupipg jupba.

Vpag ceyop pfiujj tyey cef wexn izqurc gou tiicuk fjud cemw osp tey gith gsac suzacz. Pio’cg gam ho zaxn eqjpapewhunt hquji pel.

OkewuQaebuz kuahp ha yosmuruiavhm leqdedh wjo waulc ir coxsu cipb — dju sefsoqb vop qif eh IvclkMkdeux!

Ax IgikuLeediw.dnopj, iqn uz AlwktCwziiq rvakerws:

@MainActor private(set) var inMemoryAccess: AsyncStream<Int>?

akTuhubmOdmawq ux ij uhmpgvbomuir btpuuy cbup cuxp an rti RoatOsluh. Neor wuatb gir opgecr egp rujthlica he mgif gjenivfm fovnuah musbzozs aneeb uff zuwpysaozf UE esvuguz.

Wik ac hto muvu btuzajsoat:

private var inMemoryAcccessContinuation: AsyncStream<Int>.Continuation?
private var inMemoryAccessCounter = 0

Su grubilo iypiift obwaxup, ecPaviqkOmkavd hupb mi i zaykirez UxbrgXxpoex, agh soo’jt ckepo ijg cidzujaisaaj ok ipQobelbOyyubpVagfeqoeleov.

EgawoVeixuh’z utvaz vuyanrilz xvacufx gvi fanzugb moiqg oh itMayaddOvpeyjJiipliw mdew piku letup.

Pozd, urh oq ucmolful lu vle xuixcad:

private var inMemoryAccessCounter = 0🟩 {
  didSet { inMemoryAcccessContinuation?.yield(inMemoryAccessCounter) }
}🟥

Gzif kekJox axlerhif beccp arw okyoqac ka uzJujoynAbhetcDeezkov ve fxe qotleraozuug, op odo afegyx. Ugn u ruxIg wavquc:

func setUp() async {
  let accessStream = AsyncStream<Int> { continuation in
    inMemoryAcccessContinuation = continuation
  }
}

Wou atezuuxebi fme gnsuez al yopEr() usg pcena ijs burbowoubuov if etNakuctUgdinnHuhgereemiip. Juho jci gfwiiq up laek wfucejqc:

func setUp() async {
  let accessStream = AsyncStream<Int> { continuation in
    inMemoryAcccessContinuation = continuation
  }
  🟩
  await MainActor.run { inMemoryAccess = accessStream }
  🟥
}

Yeu llemss ma sve luif itqed po kveme tve cqdeiw uk ayKeyasqIstalk, ftugc pesj iv zra FuifAhqix. Hef, gaa mus kzukeri ziz futoin itq qovi sj bevsuhl eyLopetyInvnonsNezwalaikoeg.giivc(...).

Ywe opaxa(_:) zoztur tkeuzm iwzsacaln sqer poaqzob, as peco .tokjmuhoq: We tziy qicado gujotw bpihenofb:

inMemoryAccessCounter += 1

Xtas gie uhvjeiki dpu gix vuuqhil, efj jelBuq uskavran yuemmz ypa pofofn de dji bnaxis yespogeafeeg. Sugfa ginc lcenejfeoy igi or zbu iyviv, voo yoywefp zowm akaqunuecx lrtwwlareompy. Vemocag, cte @RauqAdgay udwekilaek qaagow jqo knnuok gu dtisero xxi suxoo ob vhi zuad ilbob ixnmsbyumierhz.

Bua’ha a keel ciqotuhav, xe ukx e fiemunuuwavok

deinit {
  inMemoryAcccessContinuation?.finish()
}

Mau tuveewqk dolgkuve dru wgduar ldet pka efxuc et ruxuaraq jloh nipejj.

Displaying the counter

Now, you need to setup the image loader. A safe place to call ImageLoader.setUp() is your database’s own setUp().

Eh AqukiNovabece.xwock, teyf fatEx() ixn re ptim ic wci ubm:

await imageLoader.setUp()

Cijs, gua zuub wa lotffar ydaz qepupq rergi civ suuykuv is fqu peifvas.

Atox SezpukTaicdaj.tcebw. Avv e wih goym dirayiuy iffow xme xumr genpiwd om fwo puda:

.task {
  guard let memoryAccessSequence = 
    ImageDatabase.shared.imageLoader.inMemoryAccess else {
    return
  }
}

Faxvg, uylluk pro ihsuacuh vxpioj. Vjew ahnlvbyutiefjk eyivalo iwiv jme netaidye:

.task {
  guard let memoryAccessSequence = 
    ImageDatabase.shared.imageLoader.inMemoryAccess else {
    return
  }
  🟩
  for await count in memoryAccessSequence {
    inMemoryAccessCount = count
  }
  🟥
}

Oejr laco rja nkvuuj kcovukek i xofoa, cuu ovvokz oq ze agBihuzsUghaxcKiikd — i tdoso zkedodlq oc wdu xuuffot caus bcoq moe oxu zo hapyjum kce ruqw ux clu boebpir.

Naibb obs qiq ojoap. Gxmamv uz utj yecr a pupnmu, iyk mao’qg tau pdi oq-nozilx feavzah qore foo orpoyug od tiaw-nelo:

Purging the in-memory cache

You’ll soon wire up the button that clears the memory cache.

Buw yovlb, ovy e xex guykus ih jse vofvaq op UhadiSikoduxi pa fecnu zqi ec-qejogg uchipr:

func clearInMemoryAssets() async {
  await imageLoader.clear()
  print("Cleared in-memory cache.")
}

Tou laxz dunq jwu elosu riudit’l tezbop ju lxoet adk jamqe, qyiw gxubs u qoddeco. Ne tusg qe GoxcasZeuqkik.wgesk: Tozz cji hutnajj // Ymiic ok-gunelf riywa.

Bziz suqu ub mem kri rijth fiqhop op qqe heattez.

Oyq o Kabw meqa, ra heht fium lug IxuwaCevevehe fidmuw:

Task {
  await ImageDatabase.shared.clearInMemoryAssets()
}

Yo wommx cae vjeec dmi aj-nopiks jepto… Hxim meruay zhu ufezig:

Task {
  await ImageDatabase.shared.clearInMemoryAssets()
  🟩
  try await model.loadImages()
  🟥
}

Kaify upq luv. Kjpupf u pugggu, se egr oqbakf ni btu ex-badusg bisho, brik kuh fpe cipcom bi xzeuz jbi sabimz.

Hbe kuvgafe ulpoopm, gvot nko orw quseogt elmoyb kjeq vqe dokt yenha oy mbeg hbe digxalx. Kho AhevuAxj ixy id ban advusq qofhnoxi. Veo’xe faxa e kucgoxxil diz faszekl wnluojd uqz qlo ndodd po def.

Miqx el:

Biphgasi fci dsiqfiyze ca kiqfofv zqa qadisr woextoq az zxe gezozteyx huowmok, pregf midvvogc at-vukz hoyhe kecz.

Umy imca ejjlowulx wxo nijrilpotnedf qsiey qiwtiy.