Backport #1183 to version315: Eliminate hang due to TcpListener thread

src/NUnitEngine/nunit.engine.tests/Transport/Tcp/TcpServerTests.cs

@@ -0,0 +1,73 @@
+// Copyright (c) Charlie Poole, Rob Prouse and Contributors. MIT License - see LICENSE.txt
+
+#if NETFRAMEWORK
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Sockets;
+using System.Text;
+using System.Threading;
+using NUnit.Framework;
+
+namespace NUnit.Engine.Communication.Transports.Tcp
+{
+    public class TcpServerTests
+    {
+        private TcpServer _server;
+        private List<Socket> _serverConnections;
+
+        [SetUp]
+        public void StartServer()
+        {
+            _serverConnections = new List<Socket>();
+            _server = new TcpServer();
+            _server.ClientConnected += (c, g) => _serverConnections.Add(c);
+            _server.Start();
+        }
+
+        [TearDown]
+        public void StopServer()
+        {
+            _server.Stop();
+        }
+
+        [Test]
+        public void SingleClientConnection()
+        {
+            using (TcpClient client = new TcpClient())
+            {
+                client.Connect(_server.EndPoint);
+                client.Client.Send(new Guid().ToByteArray());
+
+                Thread.Sleep(1); // Allow the connection event to run
+                Assert.That(_serverConnections.Count, Is.EqualTo(1), "Should have received 1 connection event");
+                Assert.That(_serverConnections[0].Connected, "Server is not connected to client");
+
+                Assert.True(client.Connected, "Client is not connected to server");
+            }
+        }
+
+        [Test, Platform(Exclude = "Linux")]
+        public void MultipleClientConnections()
+        {
+            TcpClient[] clients = new[] { new TcpClient(), new TcpClient(), new TcpClient() };
+            int num = clients.Length;
+
+            foreach (var client in clients)
+            {
+                client.Connect(_server.EndPoint);
+                client.Client.Send(new Guid().ToByteArray());
+            }
+
+            Thread.Sleep(1); // Allow the connection events to run
+            Assert.That(_serverConnections.Count, Is.EqualTo(num), $"Should have received {num} connection events");
+
+            for (int i = 0; i < num; i++)
+            {
+                Assert.That(_serverConnections[i].Connected, $"Server is not connected to client {i+1}");
+                Assert.True(clients[i].Connected, $"Client {i+1} is not connected to server");
+            }
+        }
+    }
+}
+#endif

src/NUnitEngine/nunit.engine/Communication/Transports/Tcp/TcpServer.cs

@@ -14,7 +14,7 @@ public class TcpServer
 
         private const int GUID_BUFFER_SIZE = 16;
 
-        TcpListener _listenerSocket;
+        TcpListener _tcpListener;
         Thread _listenerThread;
         volatile bool _running;
 
@@ -24,17 +24,21 @@ public class TcpServer
 
         public TcpServer(int port = 0)
         {
-            _listenerSocket = new TcpListener(IPAddress.Loopback, port);
+            _tcpListener = new TcpListener(IPAddress.Loopback, port);
         }
 
-        public IPEndPoint EndPoint => (IPEndPoint)_listenerSocket.LocalEndpoint;
+        public IPEndPoint EndPoint => (IPEndPoint)_tcpListener.LocalEndpoint;
 
         public void Start()
         {
-            _listenerSocket.Start();
+            _tcpListener.Start();
             _running = true;
 
-            _listenerThread = new Thread(WaitForClientConnections);
+            _listenerThread = new Thread(WaitForClientConnections)
+            {
+                Name = "TcpListenerTread",
+                IsBackground = true
+            };
             _listenerThread.Start();
         }
 
@@ -43,7 +47,7 @@ public void Stop()
             try
             {
                 _running = false;
-                _listenerSocket.Stop();
+                _tcpListener.Stop();
             }
             catch (Exception exception)
             {
@@ -57,7 +61,7 @@ private void WaitForClientConnections()
             {
                 try
                 {
-                    var clientSocket = _listenerSocket.AcceptSocket();
+                    var clientSocket = _tcpListener.AcceptSocket();
                     if (clientSocket.Connected)
                     {
                         // Upon connection, remote agent must immediately send its Id as identification.
@@ -74,7 +78,7 @@ private void WaitForClientConnections()
                     //   1. We were trying to stop the socket
                     //   2. The connection was dropped due to some external event
                     // In either case, we stop the socket and wait a while
-                    _listenerSocket.Stop();
+                    _tcpListener.Stop();
 
                     // If we were trying to stop, that's all
                     if (!_running)
@@ -84,7 +88,7 @@ private void WaitForClientConnections()
                     Thread.Sleep(500);
                     try
                     {
-                        _listenerSocket.Start();
+                        _tcpListener.Start();
                     }
                     catch (Exception exception)
                     {