withTimeoutContinuation.swift

01-withTimeoutContinuation.swift

import Foundation

fileprivate var counter = 0

func withTimeoutUnsafeContinuation<T>(
    _ labelName: String = "NoName",
    _ timeout: TimeInterval = 2.0,
    _ fn: @escaping (UnsafeContinuation<T?, Never>) -> Void
) async -> T? {
    let nth = counter + 1
    counter = counter + 1

    let task = Task<T?, Never> {
        return await withUnsafeContinuation { continuation in
            fn(continuation)
        }
    }

    let sleep = Task {
        try await Task.sleep(for: .seconds(timeout))
        task.cancel()
    }

    let result = await task.value
    sleep.cancel()

    if task.isCancelled {
        print("[TASK][\(nth)][\(labelName)]", "Timeout canceled, return nil")
        return nil
    }
    
    print("[TASK][\(nth)][\(labelName)]", "task done")
    return result
}

02-example.swift

let timeout = 2.0
let outter = Task {
    print("start")
    let r = try? await withTimeoutUnsafeContinuation("XX", timeout) { continuation in
        print("AAA")

        let start = Date.now
        while abs(start.timeIntervalSinceNow) < 3.0 { }

        print("BBB")
        continuation.resume(returning: 999999)
    }
    print("ends", r)
}

RunLoop.current.run(mode: RunLoop.Mode.default, before: Date.now.addingTimeInterval(5.0))

// all output is:
// start
// AAA
// BBB
// [TASK][1][XX] Timeout canceled, return nil
// ends nil

// if let timeout = 4.0, all output is 
// start
// AAA
// BBB
// [TASK][1][XX] task done
// ends Optional(999999)