Fix CPU is consumed by polling frequently when there is no subscriber

playground/MSTest1/UnitTest1.cs

@@ -3,6 +3,7 @@
 
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
+using System.Threading;
 namespace MSTest1;
 
 [TestClass]
@@ -11,42 +12,6 @@ public class UnitTest1
     [TestMethod]
     public void TestMethod1()
     {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod2()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod3()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod4()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod5()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod6()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod7()
-    {
-        // Thread.Sleep(1000);
+        Thread.Sleep(10_000);
     }
 }

playground/MSTest2/MSTest2.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(TargetFrameworks);net472;net5.0;net6.0;net7.0</TargetFrameworks>
+    <TargetFrameworks>$(TargetFrameworks);net462;net472;net5.0;net6.0;net7.0</TargetFrameworks>
     <Prefer32Bit>false</Prefer32Bit>
     <IsPackable>false</IsPackable>
   </PropertyGroup>

playground/MSTest2/UnitTest1.cs

@@ -3,6 +3,8 @@
 
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
+using System.Threading;
+
 namespace MSTest2;
 
 [TestClass]
@@ -11,42 +13,6 @@ public class UnitTest2
     [TestMethod]
     public void TestMethod1()
     {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod2()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod3()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod4()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod5()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod6()
-    {
-        // Thread.Sleep(1000);
-    }
-
-    [TestMethod]
-    public void TestMethod7()
-    {
-        // Thread.Sleep(1000);
+        Thread.Sleep(10_000);
     }
 }

playground/TestPlatform.Playground/Environment.cs

@@ -14,7 +14,8 @@ internal class EnvironmentVariables
         ["VSTEST_RUNNER_DEBUG_ATTACHVS"] = "0",
         ["VSTEST_HOST_DEBUG_ATTACHVS"] = "0",
         ["VSTEST_DATACOLLECTOR_DEBUG_ATTACHVS"] = "0",
-        ["VSTEST_EXPERIMENTAL_FORWARD_OUTPUT_FEATURE"] = "0"
+        ["VSTEST_EXPERIMENTAL_FORWARD_OUTPUT_FEATURE"] = "0",
+        ["VSTEST_HOSTPRESTART_COUNT"] = "1",
     };
 
 }

playground/TestPlatform.Playground/Program.cs

@@ -35,15 +35,14 @@ static void Main()
 
         var thisAssemblyPath = Assembly.GetEntryAssembly()!.Location;
         var here = Path.GetDirectoryName(thisAssemblyPath)!;
-        var playground = Path.GetFullPath(Path.Combine(here, "..", "..", "..", ".."));
 
         var console = Path.Combine(here, "vstest.console", "vstest.console.exe");
 
         var sourceSettings = $$$"""
             <RunSettings>
                 <RunConfiguration>
 
-                    <!-- <MaxCpuCount>1</MaxCpuCount> -->
+                    <MaxCpuCount>1</MaxCpuCount>
                     <!-- <DisableParallelization>True<DisableParallelization> -->
                     <!-- <TargetPlatform>x86</TargetPlatform> -->
                     <!-- <TargetFrameworkVersion>net472</TargetFrameworkVersion> -->
@@ -88,46 +87,24 @@ static void Main()
             """;
 
         var sources = new[] {
-            Path.Combine(playground, "bin", "MSTest1", "Debug", "net472", "MSTest1.dll"),
-            Path.Combine(playground, "bin", "MSTest2", "Debug", "net472", "MSTest2.dll"),
+  //         @"S:\t\mstest85\bin\Debug\net7.0\mstest85.dll",
+  //@"S:\t\mstest85\bin\Debug\net6.0\mstest85.dll",
+  //@"S:\t\mstest85\bin\Debug\net8.0\mstest85.dll",
+  @"S:\t\nunit5\bin\Debug\net7.0\nunit5.dll",
+   @"S:\t\nunit5\bin\Debug\net8.0\nunit5.dll",
+   @"S:\t\nunit5\bin\Debug\net6.0\nunit5.dll",
             // The built in .NET projects don't now work right now in Playground, there is some conflict with Arcade.
             // But if you create one outside of Playground it will work. 
             //Path.Combine(playground, "bin", "MSTest1", "Debug", "net7.0", "MSTest1.dll"),
         };
 
-        //// Console mode
-        //// Uncomment if providing command line parameters is easier for you
-        //// than converting them to settings, or when you debug command line scenario specifically.
-        //var settingsFile = Path.GetTempFileName();
-        //try
-        //{
-        //    File.WriteAllText(settingsFile, sourceSettings);
-        //    var processStartInfo = new ProcessStartInfo
-        //    {
-        //        FileName = console,
-        //        Arguments = $"{string.Join(" ", sources)} --settings:{settingsFile} --listtests",
-        //        UseShellExecute = false,
-        //    };
-        //    EnvironmentVariables.Variables.ToList().ForEach(processStartInfo.Environment.Add);
-        //    var process = Process.Start(processStartInfo);
-        //    process.WaitForExit();
-        //    if (process.ExitCode != 0)
-        //    {
-        //        throw new Exception($"Process failed with {process.ExitCode}");
-        //    }
-        //}
-        //finally
-        //{
-        //    try { File.Delete(settingsFile); } catch { }
-        //}
-
         // design mode
         var detailedOutput = true;
         var consoleOptions = new ConsoleParameters
         {
             EnvironmentVariables = EnvironmentVariables.Variables,
-            // LogFilePath = Path.Combine(here, "logs", "log.txt"),
-            // TraceLevel = TraceLevel.Verbose,
+            LogFilePath = Path.Combine(here, "logs", "log.txt"),
+            TraceLevel = TraceLevel.Verbose,
         };
         var options = new TestPlatformOptions
         {
@@ -139,23 +116,22 @@ static void Main()
         //// TestSessions
         // r.StartTestSession(sources, sourceSettings, sessionHandler);
 #pragma warning restore CS0618 // Type or member is obsolete
-        var discoveryHandler = new PlaygroundTestDiscoveryHandler(detailedOutput);
+        //var discoveryHandler = new PlaygroundTestDiscoveryHandler(detailedOutput);
         var sw = Stopwatch.StartNew();
         // Discovery
-        r.DiscoverTests(sources, sourceSettings, options, sessionHandler.TestSessionInfo, discoveryHandler);
-        var discoveryDuration = sw.ElapsedMilliseconds;
-        Console.WriteLine($"Discovery done in {discoveryDuration} ms");
+        //r.DiscoverTests(sources, sourceSettings, options, sessionHandler.TestSessionInfo, discoveryHandler);
+        //var discoveryDuration = sw.ElapsedMilliseconds;
+        //Console.WriteLine($"Discovery done in {discoveryDuration} ms");
         sw.Restart();
         // Run with test cases and custom testhost launcher
         //r.RunTestsWithCustomTestHost(discoveryHandler.TestCases, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput), new DebuggerTestHostLauncher());
         //// Run with test cases and without custom testhost launcher
-        r.RunTests(discoveryHandler.TestCases, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput));
+        //r.RunTests(discoveryHandler.TestCases, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput));
         //// Run with sources and custom testhost launcher and debugging
-        //r.RunTestsWithCustomTestHost(sources, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput), new DebuggerTestHostLauncher());
+        // r.RunTestsWithCustomTestHost(sources, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput), new DebuggerTestHostLauncher());
         //// Run with sources
-        //r.RunTests(sources, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput));
-        var rd = sw.ElapsedMilliseconds;
-        Console.WriteLine($"Discovery: {discoveryDuration} ms, Run: {rd} ms, Total: {discoveryDuration + rd} ms");
+        r.RunTests(sources, sourceSettings, options, sessionHandler.TestSessionInfo, new TestRunHandler(detailedOutput));
+        //Console.WriteLine($"Discovery: {discoveryDuration} ms, Run: {rd} ms, Total: {discoveryDuration + rd} ms");
         // Console.WriteLine($"Settings:\n{sourceSettings}");
     }
 

src/Microsoft.TestPlatform.CommunicationUtilities/Interfaces/Communication/ICommunicationChannel.cs

@@ -2,16 +2,19 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 
+using Microsoft.VisualStudio.TestPlatform.Utilities;
+
 namespace Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces;
 
 public interface ICommunicationChannel : IDisposable
 {
     /// <summary>
     /// Event raised when data is received on the communication channel.
     /// </summary>
-    event EventHandler<MessageReceivedEventArgs> MessageReceived;
+    TrackableEvent<MessageReceivedEventArgs> MessageReceived { get; }
 
     /// <summary>
     /// Frames and sends the provided data over communication channel.
@@ -24,5 +27,66 @@ public interface ICommunicationChannel : IDisposable
     /// Notification from server/client that data is available.
     /// </summary>
     /// <returns>A <see cref="Task"/> implying async nature of the function.</returns>
-    Task NotifyDataAvailable();
+    Task NotifyDataAvailable(CancellationToken cancellationToken);
+}
+
+#pragma warning disable CA1001 // Types that own disposable fields should be disposable
+public class TrackableEvent<T>
+#pragma warning restore CA1001 // Types that own disposable fields should be disposable
+{
+    private readonly ManualResetEventSlim _slim;
+
+    internal event EventHandler<T>? Event;
+
+    public TrackableEvent()
+    {
+        _slim = new ManualResetEventSlim(Event != null);
+    }
+
+    public void Notify(object sender, T eventArgs, string traceDisplayName)
+    {
+        var e = Event;
+        if (e != null)
+        {
+            e.SafeInvoke(sender, eventArgs!, traceDisplayName);
+        }
+    }
+
+    public bool WaitForSubscriber(int timeoutMilliseconds, CancellationToken cancellationToken)
+    {
+        var _ = timeoutMilliseconds;
+        var __ = cancellationToken;
+        return Event != null;
+        //return _slim.Wait(timeoutMilliseconds, cancellationToken);
+    }
+
+    public void Subscribe(EventHandler<T> eventHandler)
+    {
+        Event += eventHandler;
+        if (Event != null)
+        {
+            _slim.Set();
+        }
+    }
+
+    public void Unsubscribe(EventHandler<T> eventHandler)
+    {
+        Event -= eventHandler;
+        if (Event == null)
+        {
+            _slim.Reset();
+        }
+    }
+}
+
+internal class UnsubscribeToken : IDisposable
+{
+    private readonly Action _unsubscribeCallback;
+    internal UnsubscribeToken(Action value) => _unsubscribeCallback = value;
+
+    public void Unsubscribe() => _unsubscribeCallback();
+    public void Dispose()
+    {
+        _unsubscribeCallback();
+    }
 }

src/Microsoft.TestPlatform.CommunicationUtilities/LengthPrefixCommunicationChannel.cs

@@ -4,12 +4,12 @@
 using System;
 using System.IO;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 
 using Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel;
 using Microsoft.VisualStudio.TestPlatform.PlatformAbstractions;
-using Microsoft.VisualStudio.TestPlatform.Utilities;
 
 namespace Microsoft.VisualStudio.TestPlatform.CommunicationUtilities;
 
@@ -37,7 +37,7 @@ public LengthPrefixCommunicationChannel(Stream stream)
     }
 
     /// <inheritdoc />
-    public event EventHandler<MessageReceivedEventArgs>? MessageReceived;
+    public TrackableEvent<MessageReceivedEventArgs> MessageReceived { get; } = new TrackableEvent<MessageReceivedEventArgs>();
 
     /// <inheritdoc />
     public Task Send(string data)
@@ -71,7 +71,7 @@ public Task Send(string data)
     }
 
     /// <inheritdoc />
-    public Task NotifyDataAvailable()
+    public Task NotifyDataAvailable(CancellationToken cancellationToken)
     {
         try
         {
@@ -85,14 +85,10 @@ public Task NotifyDataAvailable()
             // Try read data even if no one is listening to the data stream. Some server
             // implementations (like Sockets) depend on the read operation to determine if a
             // connection is closed.
-            if (MessageReceived != null)
+            if (MessageReceived.WaitForSubscriber(1000, cancellationToken))
             {
                 var data = _reader.ReadString();
-                MessageReceived.SafeInvoke(this, new MessageReceivedEventArgs { Data = data }, "LengthPrefixCommunicationChannel: MessageReceived");
-            }
-            else
-            {
-                EqtTrace.Verbose("LengthPrefixCommunicationChannel.NotifyDataAvailable: New data are waiting to be received, but there is no subscriber to be notified. Not reading them from the stream.");
+                MessageReceived.Notify(this, new MessageReceivedEventArgs { Data = data }, "LengthPrefixCommunicationChannel: MessageReceived");
             }
         }
         catch (ObjectDisposedException ex) when (!_reader.BaseStream.CanRead)

src/Microsoft.TestPlatform.CommunicationUtilities/PublicAPI/PublicAPI.Shipped.txt

@@ -100,8 +100,6 @@ Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.Disconnect
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.DisconnectedEventArgs.Error.get -> System.Exception?
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.DisconnectedEventArgs.Error.set -> void
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel
-Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel.MessageReceived -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.MessageReceivedEventArgs!>!
-Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel.NotifyDataAvailable() -> System.Threading.Tasks.Task!
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel.Send(string! data) -> System.Threading.Tasks.Task!
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationEndPoint
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationEndPoint.Connected -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ConnectedEventArgs!>!
@@ -189,8 +187,6 @@ Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.JsonDataSerializer.Se
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.Dispose() -> void
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.LengthPrefixCommunicationChannel(System.IO.Stream! stream) -> void
-Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.MessageReceived -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.MessageReceivedEventArgs!>?
-Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.NotifyDataAvailable() -> System.Threading.Tasks.Task!
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.Send(string! data) -> System.Threading.Tasks.Task!
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message
 Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message.Message() -> void
@@ -392,3 +388,13 @@ static Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.JsonDataSerial
 ~static Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Resources.Resources.UnexpectedMessage.get -> string
 ~static Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Resources.Resources.VersionCheckFailed.get -> string
 ~static Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Resources.Resources.VersionCheckTimedout.get -> string
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>.TrackableEvent() -> void
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>.Unsubscribe(System.EventHandler<T>! eventHandler) -> void
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>.WaitForSubscriber(int timeoutMilliseconds, System.Threading.CancellationToken cancellationToken) -> bool
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>.Notify(object! sender, T eventArgs, string! traceDisplayName) -> void
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<T>.Subscribe(System.EventHandler<T>! eventHandler) -> void
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel.MessageReceived.get -> Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.MessageReceivedEventArgs!>!
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.MessageReceived.get -> Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.TrackableEvent<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.MessageReceivedEventArgs!>!
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationChannel.NotifyDataAvailable(System.Threading.CancellationToken cancellationToken) -> System.Threading.Tasks.Task!
+Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.LengthPrefixCommunicationChannel.NotifyDataAvailable(System.Threading.CancellationToken cancellationToken) -> System.Threading.Tasks.Task!