Where should I run the EchoServer Sample code in my program?

[pekochun]

I get an error when I try to launch the app by writing EchoServer.run inside ViewDidLoad as below. Where should I write EchoServer.run?

import Foundation
import Socket
import Dispatch
import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let port = 1337
        let server = EchoServer(port: port)
        server.run()

        self.view.backgroundColor = .yellowColor()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

class EchoServer {
	
	static let quitCommand: String = "QUIT"
	static let shutdownCommand: String = "SHUTDOWN"
	static let bufferSize = 4096
	
	let port: Int
	var listenSocket: Socket? = nil
	var continueRunningValue = true
	var connectedSockets = [Int32: Socket]()
	let socketLockQueue = DispatchQueue(label: "com.ibm.serverSwift.socketLockQueue")
	var continueRunning: Bool {
		set(newValue) {
			socketLockQueue.sync {
				self.continueRunningValue = newValue
			}
		}
		get {
			return socketLockQueue.sync {
				self.continueRunningValue
			}
		}
	}

	init(port: Int) {
		self.port = port
	}
	
	deinit {
		// Close all open sockets...
		for socket in connectedSockets.values {
			socket.close()
		}
		self.listenSocket?.close()
	}
	
	func run() {
		
		let queue = DispatchQueue.global(qos: .userInteractive)
		
		queue.async { [unowned self] in
			
			do {
				// Create an IPV6 socket...
				try self.listenSocket = Socket.create(family: .inet6)
				
				guard let socket = self.listenSocket else {
					
					print("Unable to unwrap socket...")
					return
				}
				
				try socket.listen(on: self.port)
				
				print("Listening on port: \(socket.listeningPort)")
				
				repeat {
					let newSocket = try socket.acceptClientConnection()
					
					print("Accepted connection from: \(newSocket.remoteHostname) on port \(newSocket.remotePort)")
					print("Socket Signature: \(String(describing: newSocket.signature?.description))")
					
					self.addNewConnection(socket: newSocket)
					
				} while self.continueRunning
				
			}
			catch let error {
				guard let socketError = error as? Socket.Error else {
					print("Unexpected error...")
					return
				}
				
				if self.continueRunning {
					
					print("Error reported:\n \(socketError.description)")
					
				}
			}
		}
		dispatchMain()
	}
	
	func addNewConnection(socket: Socket) {
		
		// Add the new socket to the list of connected sockets...
		socketLockQueue.sync { [unowned self, socket] in
			self.connectedSockets[socket.socketfd] = socket
		}
		
		// Get the global concurrent queue...
		let queue = DispatchQueue.global(qos: .default)
		
		// Create the run loop work item and dispatch to the default priority global queue...
		queue.async { [unowned self, socket] in
			
			var shouldKeepRunning = true
			
			var readData = Data(capacity: EchoServer.bufferSize)
			
			do {
				// Write the welcome string...
				try socket.write(from: "Hello, type 'QUIT' to end session\nor 'SHUTDOWN' to stop server.\n")
				
				repeat {
					let bytesRead = try socket.read(into: &readData)
					
					if bytesRead > 0 {
						guard let response = String(data: readData, encoding: .utf8) else {
							
							print("Error decoding response...")
							readData.count = 0
							break
						}
						if response.hasPrefix(EchoServer.shutdownCommand) {
							
							print("Shutdown requested by connection at \(socket.remoteHostname):\(socket.remotePort)")
							
							// Shut things down...
							self.shutdownServer()
							
							return
						}
						print("Server received from connection at \(socket.remoteHostname):\(socket.remotePort): \(response) ")
						let reply = "Server response: \n\(response)\n"
						try socket.write(from: reply)
						
						if (response.uppercased().hasPrefix(EchoServer.quitCommand) || response.uppercased().hasPrefix(EchoServer.shutdownCommand)) &&
							(!response.hasPrefix(EchoServer.quitCommand) && !response.hasPrefix(EchoServer.shutdownCommand)) {
							
							try socket.write(from: "If you want to QUIT or SHUTDOWN, please type the name in all caps. 😃\n")
						}
						
						if response.hasPrefix(EchoServer.quitCommand) || response.hasSuffix(EchoServer.quitCommand) {
							
							shouldKeepRunning = false
						}
					}
					
					if bytesRead == 0 {
						
						shouldKeepRunning = false
						break
					}
					
					readData.count = 0
					
				} while shouldKeepRunning
				
				print("Socket: \(socket.remoteHostname):\(socket.remotePort) closed...")
				socket.close()
				
				self.socketLockQueue.sync { [unowned self, socket] in
					self.connectedSockets[socket.socketfd] = nil
				}
				
			}
			catch let error {
				guard let socketError = error as? Socket.Error else {
					print("Unexpected error by connection at \(socket.remoteHostname):\(socket.remotePort)...")
					return
				}
				if self.continueRunning {
					print("Error reported by connection at \(socket.remoteHostname):\(socket.remotePort):\n \(socketError.description)")
				}
			}
		}
	}
	
	func shutdownServer() {
		print("\nShutdown in progress...")

		self.continueRunning = false
		
		// Close all open sockets...
		for socket in connectedSockets.values {
			
			self.socketLockQueue.sync { [unowned self, socket] in
				self.connectedSockets[socket.socketfd] = nil
				socket.close()
			}
		}
		
		DispatchQueue.main.sync {
			exit(0)
		}
	}
}

ErrorMessage is below

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'threading violation: expected the main thread'

If I rewrite ViewDidLoad as below, I get other errors.

    override func viewDidLoad() {
        super.viewDidLoad()

        DispatchQueue.main.async
        {
            let port = 1337
            let server = EchoServer(port: port)
            server.run()
        }

        self.view.backgroundColor = .yellowColor()
    }

The details of the error are as follows.

Thread 1: EXC_BAD_ACCESS (code=1, address=0x5c)