Keep background thread alive in Editor while entering PlayMode

Fot testing purpose, I need to have tcp socket client that is connected to external server all period of Editor work. It will receive commands from external tool. So I start it by InitializeOnLoad attribute, and start it in background thread to not block the main thread. But to not finish method and to leave thread alive, I async wait endless task.

But when I start PlayMode, my thread is aborted. I've tried to use Scriptable Object with HideFlags.HideAndDontSave, but it is still died.

Example of code:

 [InitializeOnLoad]
 public class SocketClientLoader
 {
     static SocketClientLoader()
     {
         Debug.Log("SocketClientLoaderis called");
 
         EditorApplication.update += StartSocketClient;
     }
 
     private static void StartSocketClient()
     {
         EditorApplication.update -= StartSocketClient;
 
         SocketClient.Instance.Start();
     }
 }
 
 public class SocketClient : ScriptableObject, IDisposable
 {
     private bool _isRun = false;
     private Thread Thread;
     private TcpClient client;
 
     static SocketClient instance;
     public static SocketClient Instance
     {
         get
         {
             return instance ?? (instance = CreateInstance<SocketClient>());
         }
     }
 
     public async void Start()
     {
         if (_isRun) return;
 
         Instance.hideFlags = HideFlags.HideAndDontSave;
         Debug.Log("Thread is started");
         _isRun = true;
         Thread = new Thread(ProcessWork);
         Thread.IsBackground = true;
         Thread.Start();
 
         await Task.Run(() =>
         {
             while (true)
             {
                 Thread.Sleep(100);
                 if (!_isRun) return;
             }
         });
 
         Debug.Log("Thread was dead");
         _isRun = false;
     }
 
     public void ProcessWork()
     {
         //receive commands from external server
     }
 }

Can somebody help me with?

Additional: I use 2017 version with C# 4.6 experimental