Add event to RuntimeEventSource for AppContext switches

src/libraries/System.Private.CoreLib/src/System/AppContext.AnyOS.cs

@@ -1,7 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Generic;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Tracing;
 using System.IO;
 using System.Reflection;
 
@@ -30,5 +33,52 @@ private static string GetBaseDirectoryCore()
 
             return directory;
         }
+
+        internal static void LogSwitchValues(RuntimeEventSource ev)
+        {
+            if (s_switches is not null)
+            {
+                lock (s_switches)
+                {
+                    foreach (KeyValuePair<string, bool> kvp in s_switches)
+                    {
+                        // Convert bool to int because it's cheaper to log (no boxing)
+                        ev.LogAppContextSwitch(kvp.Key, kvp.Value ? 1 : 0);
+                    }
+                }
+            }
+
+            if (s_dataStore is not null)
+            {
+                lock (s_dataStore)
+                {
+                    if (s_switches is not null)
+                    {
+                        lock (s_switches)
+                        {
+                            LogDataStore(s_switches);
+                        }
+                    }
+                    else
+                    {
+                        LogDataStore(null);
+                    }
+
+                    void LogDataStore(Dictionary<string, bool>? switches)
+                    {
+                        Debug.Assert(s_dataStore is not null);
+                        foreach (KeyValuePair<string, object?> kvp in s_dataStore)
+                        {
+                            if (kvp.Value is string s &&
+                                bool.TryParse(s, out bool isEnabled) &&
+                                switches?.ContainsKey(kvp.Key) != true)
+                            {
+                                ev.LogAppContextSwitch(kvp.Key, isEnabled ? 1 : 0);
+                            }
+                        }
+                    }
+                }
+            }
+        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs

@@ -14,6 +14,11 @@ internal sealed partial class RuntimeEventSource : EventSource
     {
         internal const string EventSourceName = "System.Runtime";
 
+        public static class Keywords
+        {
+            public const EventKeywords AppContext = (EventKeywords)0x1;
+        }
+
         private static RuntimeEventSource? s_RuntimeEventSource;
         private PollingCounter? _gcHeapSizeCounter;
         private IncrementingPollingCounter? _gen0GCCounter;
@@ -50,6 +55,17 @@ public static void Initialize()
         // as you can't make a constructor partial.
         private RuntimeEventSource(int _) { }
 
+        private enum EventId : int
+        {
+            AppContextSwitch = 1
+        }
+
+        [Event((int)EventId.AppContextSwitch, Level = EventLevel.Informational, Keywords = Keywords.AppContext)]
+        internal void LogAppContextSwitch(string switchName, int value)
+        {
+            base.WriteEvent((int)EventId.AppContextSwitch, switchName, value);
+        }
+
         protected override void OnEventCommand(EventCommandEventArgs command)
         {
             if (command.Command == EventCommand.Enable)
@@ -87,6 +103,8 @@ protected override void OnEventCommand(EventCommandEventArgs command)
                 _ilBytesJittedCounter ??= new PollingCounter("il-bytes-jitted", this, () => System.Runtime.JitInfo.GetCompiledILBytes()) { DisplayName = "IL Bytes Jitted", DisplayUnits = "B" };
                 _methodsJittedCounter ??= new PollingCounter("methods-jitted-count", this, () => System.Runtime.JitInfo.GetCompiledMethodCount()) { DisplayName = "Number of Methods Jitted" };
                 _jitTimeCounter ??= new IncrementingPollingCounter("time-in-jit", this, () => System.Runtime.JitInfo.GetCompilationTime().TotalMilliseconds) { DisplayName = "Time spent in JIT", DisplayUnits = "ms", DisplayRateTimeScale = new TimeSpan(0, 0, 1) };
+
+                AppContext.LogSwitchValues(this);
             }
 
         }

src/tests/tracing/eventcounter/runtimecounters.cs

@@ -54,7 +54,9 @@ protected override void OnEventSourceCreated(EventSource source)
             {
                 Dictionary<string, string> refreshInterval = new Dictionary<string, string>();
                 refreshInterval.Add("EventCounterIntervalSec", "1");
-                EnableEvents(source, EventLevel.Informational, (EventKeywords)(-1), refreshInterval);
+                EnableEvents(source, EventLevel.Informational,
+                    (EventKeywords)(-1 & (~1 /* RuntimeEventSource.Keywords.AppContext */)),
+                    refreshInterval);
             }
         }
 
@@ -100,7 +102,7 @@ public static int Main(string[] args)
             // Create an EventListener.
             using (RuntimeCounterListener myListener = new RuntimeCounterListener())
             {
-                Thread.Sleep(3000); 
+                Thread.Sleep(3000);
                 if (myListener.Verify())
                 {
                     Console.WriteLine("Test passed");

src/tests/tracing/runtimeeventsource/NativeRuntimeEventSourceTest.cs

@@ -0,0 +1,114 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+using System.Diagnostics.Tracing;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Tracing.Tests.Common;
+
+namespace Tracing.Tests
+{
+    public sealed class NativeRuntimeEventSourceTest
+    {
+        static int Main(string[] args)
+        {
+            SimpleEventListener.EnableKeywords = (EventKeywords)0;
+            using (SimpleEventListener noEventsListener = new SimpleEventListener("NoEvents"))
+            {
+                // Create an EventListener.
+                SimpleEventListener.EnableKeywords = (EventKeywords)0x4c14fccbd;
+                using (SimpleEventListener listener = new SimpleEventListener("Simple"))
+                {
+                    // Trigger the allocator task.
+                    System.Threading.Tasks.Task.Run(new Action(Allocator));
+
+                    // Wait for events.
+                    Thread.Sleep(1000);
+
+                    // Generate some GC events.
+                    GC.Collect(2, GCCollectionMode.Forced);
+
+                    // Wait for more events.
+                    Thread.Sleep(1000);
+
+                    // Ensure that we've seen some events.
+                    Assert.True("listener.EventCount > 0", listener.EventCount > 0);
+                }
+
+                // Generate some more GC events.
+                GC.Collect(2, GCCollectionMode.Forced);
+
+                // Ensure that we've seen no events.
+                Assert.True("noEventsListener.EventCount == 0", noEventsListener.EventCount == 0);
+            }
+
+            return 100;
+        }
+
+        private static void Allocator()
+        {
+            while (true)
+            {
+                for(int i=0; i<1000; i++)
+                    GC.KeepAlive(new object());
+
+                Thread.Sleep(10);
+            }
+        }
+    }
+
+    internal sealed class SimpleEventListener : EventListener
+    {
+        private string m_name;
+
+        // Keep track of the set of keywords to be enabled.
+        public static EventKeywords EnableKeywords
+        {
+            get;
+            set;
+        }
+
+        public SimpleEventListener(string name)
+        {
+            m_name = name;
+        }
+
+        public int EventCount { get; private set; } = 0;
+
+        protected override void OnEventSourceCreated(EventSource eventSource)
+        {
+            if (eventSource.Name.Equals("Microsoft-Windows-DotNETRuntime"))
+            {
+                if (EnableKeywords != 0)
+                {
+                    // Enable events.
+                    EnableEvents(eventSource, EventLevel.Verbose, EnableKeywords);
+                }
+                else
+                {
+                    // Enable the provider, but not any keywords, so we should get no events as long as no rundown occurs.
+                    EnableEvents(eventSource, EventLevel.Critical, EnableKeywords);
+                }
+            }
+        }
+
+        protected override void OnEventWritten(EventWrittenEventArgs eventData)
+        {
+            Console.WriteLine($"[{m_name}] ThreadID = {eventData.OSThreadId} ID = {eventData.EventId} Name = {eventData.EventName}");
+            Console.WriteLine($"TimeStamp: {eventData.TimeStamp.ToLocalTime()}");
+            Console.WriteLine($"LocalTime: {DateTime.Now}");
+            Console.WriteLine($"Difference: {DateTime.UtcNow - eventData.TimeStamp}");
+            Assert.True("eventData.TimeStamp <= DateTime.UtcNow", eventData.TimeStamp <= DateTime.UtcNow);
+            for (int i = 0; i < eventData.Payload.Count; i++)
+            {
+                string payloadString = eventData.Payload[i] != null ? eventData.Payload[i].ToString() : string.Empty;
+                Console.WriteLine($"\tName = \"{eventData.PayloadNames[i]}\" Value = \"{payloadString}\"");
+            }
+            Console.WriteLine("\n");
+
+            EventCount++;
+        }
+    }
+}