Hello, I'd like to find an available TCP port. I came up with this code: #!/usr/bin/env swift import Foundation import Network func findAvailablePort() -> UInt16 { let semaphore = DispatchSemaphore(value: 0) let listener = try! NWListener(using: .tcp, on: .any) listener.stateUpdateHandler = { state in switch state { case .ready: semaphore.signal() case .failed(let e): fatalError(e.localizedDescription) default: break } } listener.newConnectionHandler = { conn in } listener.start(queue: .global()) let timeout = DispatchTime.now() + DispatchTimeInterval.seconds(5) if semaphore.wait(timeout: timeout) == .timedOut { fatalError("timeout") } return listener.port!.rawValue } print(findAvailablePort()) Any feedback, especially around error handling, would be very appreciated. (The two error conditions I've identified, network error and semaphore timeout, seem unlikely to hit so I reached for fatalError.) To give some more context, I'm writing an application with processes A and B. A starts B via Process(). B will listen on a TCP socket but A needs to know which one. (I'd rather not use stdio to let it know.) So A will find a free tcp port, start B, and pass port in argv. There's obviously a possible race condition between finding the free port and listening on it but it seems unlikely to hit given the OS doesn't seem to "recycle" free ports right away.