Imported Upstream version 5.8.0.22

Former-commit-id: df344e34b07851d296efb3e6604c8db42b6f7aa3

mcs/class/test-helpers/NetworkHelpers.cs

@@ -1,22 +1,48 @@
 using System;
 using System.Net;
 using System.Net.Sockets;
+using System.Collections.Generic;
 
 namespace MonoTests.Helpers {
 
 	public static class NetworkHelpers
 	{
+		static Random rndPort = new Random ();
+		static HashSet<int> portsTable = new HashSet<int> ();
+
 		public static int FindFreePort ()
 		{
-			TcpListener l = new TcpListener(IPAddress.Loopback, 0);
-			l.Start();
-			int port = ((IPEndPoint)l.LocalEndpoint).Port;
-			l.Stop();
-			return port;
+			return LocalEphemeralEndPoint ().Port;
 		}
+
 		public static IPEndPoint LocalEphemeralEndPoint ()
 		{
-			return new IPEndPoint (IPAddress.Loopback, FindFreePort());
+			int counter = 0;
+
+			while (counter < 1000) {
+				var testingPort = rndPort.Next (10000, 60000);
+
+				var ep = new IPEndPoint (IPAddress.Loopback, testingPort);
+
+				lock (portsTable) {
+					if (portsTable.Contains (testingPort))
+						continue;
+
+					++counter;
+
+					try {
+						using (var socket = new Socket (ep.AddressFamily, SocketType.Stream, ProtocolType.Tcp)) {
+							socket.Bind (ep);
+							socket.Close ();
+						}
+
+						portsTable.Add (testingPort);
+						return ep;
+					} catch (SocketException) { }
+				}
+			}
+
+			throw new ApplicationException ($"Could not find available local port after {counter} retries");
 		}
 	}
 }