Task & .task
구현 목표
1. async 데이터를 받아오는 코드를 실행할 때 Task 안에 넣어서 실행하는 방법
2. Task의 우선순위 파악하기
3. Task 내부의 스레드 환경 확인하기
4. Task 내부 작업을 취소하는 방법 확인하기
구현 태스크
- 서로 다른
Task를 실행할 때 우선순위를 커스텀하기 Task.yield()사용해보기Task.detached()사용해보기Task.cancel()사용해보기.task사용해보기
핵심 코드
func fetchImage() async {
guard let url = getURL() else { return }
do {
let (data, _) = try await URLSession.shared.data(from: url, delegate: nil)
await MainActor.run {
self.image = UIImage(data: data)
}
} catch {
print(error.localizedDescription)
}
}- 데이터를
async await로 받기 - 받은 데이터를 UI가 사용할 데이터로 할당하는 부분은
MainActor를 통해 동기화 이슈 사전에 해결하기
.task {
try? await Task.sleep(nanoseconds: 5_000_000_000)
await viewModel.fetchImage()
await viewModel.fetchImage2()
}.task블럭을 통해 컴파일러가 자체적으로cancel상황을 고려함- 작업 도중 취소 시 비동기적 데이터를 다운로드받는 동작을 지속하는 게 아니라 중도 멈춤
소스 코드
import SwiftUI
class TaskBootCampViewModel: ObservableObject {
@Published var image: UIImage? = nil
@Published var image2: UIImage? = nil
func getURL() -> URL? {
guard let url = URL(string: "https://picsum.photos/1000") else { return nil }
return url
}
func fetchImage() async {
guard let url = getURL() else { return }
do {
let (data, _) = try await URLSession.shared.data(from: url, delegate: nil)
await MainActor.run {
self.image = UIImage(data: data)
}
} catch {
print(error.localizedDescription)
}
}
func fetchImage2() async {
guard let url = getURL() else { return }
do {
let (data, _) = try await URLSession.shared.data(from: url, delegate: nil)
await MainActor.run {
self.image2 = UIImage(data: data)
}
} catch {
print(error.localizedDescription)
}
}
func printTaskPriority() {
Task(priority: .low) {
print("LOW: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .medium) {
print("MEDIUM: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .high) {
print("HIGH: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .background) {
print("BACKGROUND: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .userInitiated) {
print("USERINITIATED: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .utility) {
print("UTILITY: \(Thread.current) : \(Task.currentPriority)")
}
/*
HIGH: <NSThread: 0x600002266980>{number = 4, name = (null)} : TaskPriority(rawValue: 25)
USERINITIATED: <NSThread: 0x600002266980>{number = 4, name = (null)} : TaskPriority(rawValue: 25)
MEDIUM: <NSThread: 0x60000224bc80>{number = 6, name = (null)} : TaskPriority(rawValue: 21)
LOW: <NSThread: 0x60000223d9c0>{number = 5, name = (null)} : TaskPriority(rawValue: 17)
UTILITY: <NSThread: 0x60000223d9c0>{number = 5, name = (null)} : TaskPriority(rawValue: 17)
BACKGROUND: <NSThread: 0x60000224bc80>{number = 6, name = (null)} : TaskPriority(rawValue: 9)
*/
}
func printTaskPrioirty2() async {
Task(priority: .low) {
print("LOW: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .medium) {
print("MEDIUM: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .high) {
// try? await Task.sleep(nanoseconds:2_000_000_00)
await Task.yield()
print("HIGH: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .background) {
print("BACKGROUND: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .userInitiated) {
print("USERINITIATED: \(Thread.current) : \(Task.currentPriority)")
}
Task(priority: .utility) {
print("UTILITY: \(Thread.current) : \(Task.currentPriority)")
}
/*
USERINITIATED: <NSThread: 0x600003c5a400>{number = 7, name = (null)} : TaskPriority(rawValue: 25)
MEDIUM: <NSThread: 0x600003c5f7c0>{number = 5, name = (null)} : TaskPriority(rawValue: 21)
LOW: <NSThread: 0x600003c469c0>{number = 6, name = (null)} : TaskPriority(rawValue: 17)
UTILITY: <NSThread: 0x600003c469c0>{number = 6, name = (null)} : TaskPriority(rawValue: 17)
BACKGROUND: <NSThread: 0x600003c469c0>{number = 6, name = (null)} : TaskPriority(rawValue: 9)
HIGH: <NSThread: 0x600003c469c0>{number = 6, name = (null)} : TaskPriority(rawValue: 25)
-> YEILD THREAD
*/
}
func printParentChildTask() {
Task(priority: .low) {
print("Parent: \(Thread.current) : \(Task.currentPriority)")
Task {
print("Child: \(Thread.current) : \(Task.currentPriority)")
}
Task.detached(priority: .high) {
print("Child Detached: \(Thread.current) : \(Task.currentPriority)")
}
}
/*
Parent: <NSThread: 0x600002b7cc80>{number = 6, name = (null)} : TaskPriority(rawValue: 17)
Child Detached: <NSThread: 0x600002b11a00>{number = 4, name = (null)} : TaskPriority(rawValue: 25)
Child: <NSThread: 0x600002b7cc80>{number = 6, name = (null)} : TaskPriority(rawValue: 17)
-> Don't use detached method if possible as official Doc says
*/
}
func resetImages() {
image = nil
image2 = nil
}
}- 일반적인
async await를 활용한 데이터 패치 함수 - 태스크에 우선순위를 할당 가능
Task.yield()를 통해 태스크를 할당하거나 양보하는 부분을 지정 → 우선순위가 가장 높은HIGH스레드는printTaskPriority에서 작동한 바와 같이 다른 스레드보다 먼저 실행되어야 하지만printTaskPriority2에서 작동한 바와 같이 스레드 양보를 통해 마지막에 실행됨Task.detached를 통해 부모 태스크와 자식 태스크를 분리 가능, 자식 태스크의 우선순위를 커스텀 가능 → 공식 문서에 따르자면 가능한 사용하지 않아야 할 방법
struct TaskBootCamp: View {
@StateObject private var viewModel = TaskBootCampViewModel()
@State private var count: Int = 0
@State private var timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
@State private var fetchImageTask: Task<(), Never>? = nil
var body: some View {
NavigationView {
ZStack {
NavigationLink {
imageView
} label: {
Text("Image Download")
}
}
}
}
}
extension TaskBootCamp {
private var imageView: some View {
VStack {
Text("TIMER COUNT: \(count)")
if let image = viewModel.image {
Image(uiImage: image)
.resizable()
.scaledToFit()
}
if let image2 = viewModel.image2 {
Image(uiImage: image2)
.resizable()
.scaledToFit()
}
}
.onReceive(timer, perform: { _ in
count = count + 1 <= 5 ? count + 1 : count
})
.onAppear {
viewModel.resetImages()
count = 0
// taskFetchImages2()
}
// .onDisappear {
// count = 0
// fetchImageTask?.cancel()
// }
.task {
try? await Task.sleep(nanoseconds: 5_000_000_000)
await viewModel.fetchImage()
await viewModel.fetchImage2()
}
}
func taskFetchImages() {
Task {
try? await Task.sleep(nanoseconds: 5_000_000_000)
await viewModel.fetchImage()
await viewModel.fetchImage2()
}
}
func taskFetchImages2() {
fetchImageTask = Task {
try? await Task.sleep(nanoseconds: 5_000_000_000)
await viewModel.fetchImage()
}
}
}TaskBootCamp뷰 내부에서 네비게이션 뷰 활용, 유저의 중도 취소(백 버튼 기능) →Task.cancel상황을 구현
구현 화면
JUST DO IT