BackgroundExecutorTestApp

BackgroundExecutorApp.swift

import SwiftUI
import Dispatch

// A simple app to verify https://mastodon.social/@calicoding/112118821467209266
// Allows you to check using Swift Tasks, or Dispatch Queues.
// 
// I found this to not be the case, but maybe this isn't realistic?
// When compiled on Xcode 15.3 (either debug or release) and run on iOS 17.4,
// background QoS tasks are still executed even when Low Power Mode is enabled.

@main
struct BackgroundExecutorApp: App {
    var body: some Scene {
        WindowGroup {
            VStack {
                Text("Low Power Mode: \(ProcessInfo.processInfo.isLowPowerModeEnabled)") // Yes, this won't automatically update.
                TaskExecutor()
                Divider()
                DispatchExecutor()
                Spacer()
            }
            .padding()
        }
    }
}

enum TaskState: Sendable {
    case notRunning
    case queued
    case finished

    var text: String {
        switch self {
        case .notRunning: "Not Running"
        case .queued: "Queued"
        case .finished: "Finished"
        }
    }
}

@MainActor
struct TaskExecutor: View {
    @State var state: TaskState = .notRunning

    var body: some View {
        VStack {
            Text("Using Swift Task")
            HStack {
                Text(verbatim: state.text)
                Button("Run") {
                    state = .queued
                    Task.detached(priority: .background) {
                        print("Running in background swift task")
                        await MainActor.run {
                            state = .finished
                        }
                    }
                }.disabled(state == .queued)
            }
        }
    }
}

@MainActor
struct DispatchExecutor: View {
    @State var state: TaskState = .notRunning

    var body: some View {
        VStack {
            Text("Using DispatchQueue")
            HStack {
                Text(verbatim: state.text)
                Button("Run") {
                    state = .queued
                    DispatchQueue.global(qos: .background).async {
                        print("Running in background dispatch queue")
                        DispatchQueue.main.async {
                            state = .finished
                        }
                    }
                }.disabled(state == .queued)
            }
        }
    }
}