fix network methods not shutting down

Mono.Nat/NatUtility.cs

@@ -43,7 +43,6 @@ namespace Mono.Nat
 {
     public static class NatUtility
     {
-        private static ManualResetEvent searching;
         public static event EventHandler<DeviceEventArgs> DeviceFound;
         public static event EventHandler<DeviceEventArgs> DeviceLost;
 
@@ -68,8 +67,6 @@ namespace Mono.Nat
                 NatProtocol.Pmp
             };
 
-            searching = new ManualResetEvent(false);
-
             controllers = new List<ISearcher>();
             controllers.Add(PmpSearcher.Instance);
 
@@ -86,8 +83,6 @@ namespace Mono.Nat
                             DeviceLost(sender, args);
                     };
                 });
-
-            Task.Factory.StartNew(SearchAndListen, TaskCreationOptions.LongRunning);
         }
 
         internal static void Log(string format, params object[] args)
@@ -97,12 +92,10 @@ namespace Mono.Nat
                 logger.Debug(format, args);
         }
 
-        private static async Task SearchAndListen()
+        private static async Task SearchAndListen(CancellationToken cancellationToken)
         {
-            while (true)
+            while (!cancellationToken.IsCancellationRequested)
             {
-                searching.WaitOne();
-
                 try
                 {
                     var enabledProtocols = EnabledProtocols.ToList();
@@ -144,14 +137,45 @@ namespace Mono.Nat
             }
         }
 
+        private static CancellationTokenSource _currentCancellationTokenSource;
+        private static object _runSyncLock = new object();
         public static void StartDiscovery()
         {
-            searching.Set();
+            lock (_runSyncLock)
+            {
+                if (_currentCancellationTokenSource == null)
+                {
+                    return;
+                }
+
+                var tokenSource = new CancellationTokenSource();
+
+                _currentCancellationTokenSource = tokenSource;
+                //Task.Factory.StartNew(() => SearchAndListen(tokenSource.Token), tokenSource.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
+            }
         }
 
         public static void StopDiscovery()
         {
-            searching.Reset();
+            lock (_runSyncLock)
+            {
+                var tokenSource = _currentCancellationTokenSource;
+
+                if (tokenSource != null)
+                {
+                    try
+                    {
+                        tokenSource.Cancel();
+                        tokenSource.Dispose();
+                    }
+                    catch
+                    {
+
+                    }
+
+                    _currentCancellationTokenSource = null;
+                }
+            }
         }
 
         //checks if an IP address is a private address space as defined by RFC 1918
@@ -159,7 +183,8 @@ namespace Mono.Nat
         {
             byte[] ba = address.GetAddressBytes();
 
-			switch ((int)ba[0]) {
+            switch ((int)ba[0])
+            {
                 case 10:
                     return true; //10.x.x.x
                 case 172: