Swift concurrency: multiple await for single result with loop

multiple-await-with-loop.swift

import Foundation

func generateSecureHash() async -> UUID {
    print("Generating hash")
    do {
        try await Task.sleep(for: .seconds(100))
    } catch {
        print("Sleep: \(error)")
    }
    print("Generating hash: done")
    return UUID()
}

class SomeService {
    private var hash: UUID?
    private var isGeneratingHash = false
    
    func doX() async {
        let hash = await generateHash()
        
        print("doX: \(hash)")
    }

    func doY() async {
        let hash = await generateHash()
        
        print("doY: \(hash)")
    }
    
    private func generateHash() async -> UUID {
        while isGeneratingHash {
            // await Task.yield() // high CPU usage
            do {
                // try await Task.sleep(for: .milliseconds(1)) // high CPU usage
                try await Task.sleep(for: .milliseconds(100)) // low CPU usage, high latency
            } catch {
                print("Sleep: \(error)")
            }
        }
        if let hash { return hash }
        
        isGeneratingHash = true
        defer { isGeneratingHash = false }
        
        let hash = await generateSecureHash()
        self.hash = hash
        return hash
    }
}

Task.detached {
    let service = SomeService()
    async let x: Void = service.doX()
    async let y: Void = service.doY()
    _ = await [x, y]
}

let sigintSrc = DispatchSource.makeSignalSource(signal: SIGINT, queue: .main)
sigintSrc.setEventHandler {
    print("")
    exit(0)
}
sigintSrc.resume()

RunLoop.current.run()