Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/ActivityIdHelper.cs

@@ -0,0 +1,95 @@
+//------------------------------------------------------------------------------
+// <copyright file="ActivityIdHelper.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Diagnostics.Tracing;
+    using System.Runtime.CompilerServices;
+    using System.Threading;
+
+    internal sealed class ActivityIdHelper {
+
+        private delegate Guid GetCurrentDelegate();
+        private delegate void SetAndDestroyDelegate(Guid activityId);
+        private delegate void SetAndPreserveDelegate(Guid activityId, out Guid oldActivityThatWillContinue);
+
+        // Note to callers: this field can be null.
+        internal static readonly ActivityIdHelper Instance = GetSingleton();
+
+        private static readonly Guid _baseGuid = Guid.NewGuid();
+        private static long _counter;
+
+        private readonly GetCurrentDelegate _getCurrentDel;
+        private readonly SetAndDestroyDelegate _setAndDestroyDel;
+        private readonly SetAndPreserveDelegate _setAndPreserveDel;
+
+        // use the factory to create an instance of this type
+        private ActivityIdHelper(GetCurrentDelegate getCurrentDel, SetAndDestroyDelegate setAndDestroyDel, SetAndPreserveDelegate setAndPreserveDel) {
+            _getCurrentDel = getCurrentDel;
+            _setAndDestroyDel = setAndDestroyDel;
+            _setAndPreserveDel = setAndPreserveDel;
+        }
+
+        // Gets the current thread's activity ID.
+        public Guid CurrentThreadActivityId {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get { return _getCurrentDel(); }
+        }
+
+        private static ActivityIdHelper GetSingleton() {
+            try {
+                // The mscorlib APIs we depend on weren't added until Blue, so we can't
+                // take a direct dependency. Need to light up instead.
+
+                var getCurrentDel = (GetCurrentDelegate)Delegate.CreateDelegate(
+                    typeof(GetCurrentDelegate), typeof(EventSource), "get_CurrentThreadActivityId", ignoreCase: false, throwOnBindFailure: false);
+
+                var setAndDestroyDel = (SetAndDestroyDelegate)Delegate.CreateDelegate(
+                    typeof(SetAndDestroyDelegate), typeof(EventSource), "SetCurrentThreadActivityId", ignoreCase: false, throwOnBindFailure: false);
+
+                var setAndPreserveDel = (SetAndPreserveDelegate)Delegate.CreateDelegate(
+                    typeof(SetAndPreserveDelegate), typeof(EventSource), "SetCurrentThreadActivityId", ignoreCase: false, throwOnBindFailure: false);
+
+                if (getCurrentDel != null && setAndDestroyDel != null && setAndPreserveDel != null) {
+                    return new ActivityIdHelper(getCurrentDel, setAndDestroyDel, setAndPreserveDel);
+                }
+            }
+            catch {
+                // exceptions are not fatal; we just won't be able to call the new APIs
+            }
+
+            return null;
+        }
+
+        // Disposes of the thread's existing activity ID, then sets the new activity ID on this thread.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void SetCurrentThreadActivityId(Guid activityId) {
+            _setAndDestroyDel(activityId);
+        }
+
+        // Suspends (but does not dispose of) the thread's existing activity ID, then sets a new activity ID on this thread.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void SetCurrentThreadActivityId(Guid activityId, out Guid oldActivityThatWillContinue) {
+            _setAndPreserveDel(activityId, out oldActivityThatWillContinue);
+        }
+
+        // !! SECURITY WARNING !!
+        // The GUIDs created by this method are predictable and should be used ONLY for tracing.
+        // Any other use (such as leaking them to the user) constitutes information disclosure.
+        //
+        // This is a perf-sensitive method since it could potentially be called many times per
+        // request. Guid.NewGuid() is slow since it eventually calls CAPI, and we did actually
+        // see it show up as a bottleneck when developing MVC 2. The below implementation has
+        // measurably better performance characteristics than calling the other Guid ctors.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe Guid UnsafeCreateNewActivityId() {
+            Guid guidCopy = _baseGuid;
+            *(long*)(&guidCopy) ^= Interlocked.Increment(ref _counter); // operate on the copy, not the original
+            return guidCopy;
+        }
+
+    }
+}