How return value from DispatchQueue

Question

everyone,

using the Swiftyping library, I perform a ping test n times on an ip address that I give to the function via a Post call.

 routes.post("ping") { req async throws -> PingTestResult in
        
        var testResult = PingTestResult(latency: [], Date: "", packetsTrasmitted: 0, packetsReceived: 0, packetLoss: 0.0, rtMin: "", rtMax: "", rtAvg: "", rtStdDev: "")
        
        let pingConfig = try req.content.decode(PingConfig.self)
        
        print("\nhostname: \(pingConfig.host!), to be ping: \(pingConfig.n!)\n")
        
        testResult = await ping.waitForDataFromPing(hostname: pingConfig.host!, n: pingConfig.n!)
        
        return testResult
    }

Here the function to make the ping test:

func startPinging(hostname: String, n: Int) async throws  {
            
    do{
        ping = try SwiftyPing(host: hostname, configuration: PingConfiguration(interval: 1.0,with: 1), queue: DispatchQueue.global())
        ping?.targetCount = n
           
        ping?.observer = { response in
            DispatchQueue.main.async {

                
                var latency = String(format: "%.3f ms", response.duration * 1000)
                
                if let error = response.error {
                    if error == .requestTimeout{
                        latency = "Timeout \(latency)"
                    } else{
                        print(error)
                        latency = error.localizedDescription
                    }
                }
                let message = "\nPing Test #\(response.trueSequenceNumber): \(latency)\n"
               
                
                self.latArray.append(latency)
                
                print(message)
                
            }
            
        }
         
        ping?.finished = {(result) in
            DispatchQueue.main.async {
                
                let dateformatter = DateFormatter()
                dateformatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
                dateformatter.timeZone = TimeZone.current
                
                let date = dateformatter.string(from: self.currentdate)
                
                let rtMin = String(format: "%.3f ms", result.roundtrip!.minimum * 1000)
                
                let rtMax = String(format: "%.3f ms", result.roundtrip!.maximum * 1000)
                
                let rtAvg = String(format: "%.3f ms", result.roundtrip!.average * 1000)
                
                let rtStdDev = String(format: "%.3f ms", result.roundtrip!.standardDeviation * 1000)
                
                var message = "\n--- \(hostname) ping statistics ---\n"
                message += "\nTest Date: \(date)\n"
                message += "\nTest Performed: \(n)\n"
                message += "\nPackets Trasmitted: \(result.packetsTransmitted)\n"
                message += "\nPackets Received: \(result.packetsReceived)\n"
                if let loss = result.packetLoss{
                    message += String(format: "\nPacket Loss: %.1f%% \n", loss * 100)
                } else {
                    message += "\n"
                }
           
                
                if result.roundtrip != nil {
                    message += "\nRound-trip Min: \(rtMin)"
                    message += "\nRound-trip Min: \(rtMax)"
                    message += "\nRound-trip Min: \(rtAvg)"
                    message += "\nRound-trip Min: \(rtStdDev)"
                }
            
    
            print(message)

            self.pingResult = PingTestResult(latency: self.latArray, Date: date, packetsTrasmitted: result.packetsTransmitted, packetsReceived: result.packetsReceived, packetLoss: result.packetLoss! * 100, rtMin: rtMin, rtMax: rtMax, rtAvg: rtAvg, rtStdDev: rtStdDev)
                
            }   
        }
        
        try self.ping?.startPinging()
        
        
    } catch {
        print("Pinging \(hostname) not possibile. Error: \(error.localizedDescription)")
    }

}

    func waitForDataFromPing(hostname: String, n: Int) async -> PingTestResult {
    try? await self.startPinging(hostname: hostname, n: n)
    return self.pingResult
}

the problem I am experiencing is that when the ping test ends, I cannot return the test data. Is there any way by which the result values can be returned from the DispatchQueue?

enter image description here

Use escaping closure to get your desired result. Here is the link https://stackoverflow.com/questions/39504180/escaping-closures-in-swift — Muhammad Salman, Oct 24 '22 at 11:04
You can’t. You should move completely from GCD to Swift Concurrency using `Task`s, `Actor`s and `Continuation`s — vadian, Oct 24 '22 at 11:25
I mostly agree with @vadian, but if for some reason you need (or really want) to stick to GCD, and want to return a value from the `async` call instead of continuing your code that uses it in the closure, you'll need some kind of Promise/Future. There are several out there, and I have my own ([Async](https://github.com/chipjarred/Async)). I like mine because in addition to a completion-handler style, it allows storing away the future as a place holder value, similar to C++'s `std::future`, which I find useful for certain situations, but I use it less since Swift added `async`/`await`. — Chip Jarred, Oct 24 '22 at 12:25
thanks for the tips, the use of continuations solved my problem — MichaelG, Nov 02 '22 at 09:39

How return value from DispatchQueue

0 Answers0