NH-3905 - Replacing ThreadLocal by AsyncLocal, and adjusting tests.

Author: fredericDelaporte

src/NHibernate.Test/NHSpecificTest/Logs/LogsFixture.cs

@@ -31,7 +31,7 @@ protected override string MappingsAssembly
 		[Test]
 		public void WillGetSessionIdFromSessionLogs()
 		{
-			ThreadContext.Properties["sessionId"] = new SessionIdCapturer();
+			GlobalContext.Properties["sessionId"] = new SessionIdCapturer();
 
 			using (var spy = new TextLogSpy("NHibernate.SQL", "%message | SessionId: %property{sessionId}"))
 			using (var s = Sfi.OpenSession())
@@ -45,8 +45,11 @@ public void WillGetSessionIdFromSessionLogs()
 			}
 		}
 
-		public class SessionIdCapturer
+		// IFixingRequired interface ensures the value is evaluated at log time rather than at log buffer flush time.
+		public class SessionIdCapturer : IFixingRequired
 		{
+			public object GetFixedObject() => ToString();
+
 			public override string ToString()
 			{
 				return SessionIdLoggingContext.SessionId.ToString();

src/NHibernate/Impl/SessionIdLoggingContext.cs

@@ -1,38 +1,38 @@
 using System;
+using System.Threading;
 
 namespace NHibernate.Impl
 {
 	public class SessionIdLoggingContext : IDisposable
 	{
-		[ThreadStatic]
-		private static Guid? CurrentSessionId;
+		private static readonly AsyncLocal<Guid?> _currentSessionId = new AsyncLocal<Guid?>();
 
-		private readonly Guid? oldSessonId;
+		private readonly Guid? _oldSessonId;
 
 		public SessionIdLoggingContext(Guid id)
 		{
-			oldSessonId = SessionId;
+			_oldSessonId = SessionId;
 			SessionId = id;
 		}
 
 		/// <summary>
-		/// We always set the result to use a thread static variable, on the face of it,
+		/// We always set the result to use an async local variable, on the face of it,
 		/// it looks like it is not a valid choice, since ASP.Net and WCF may decide to switch
 		/// threads on us. But, since SessionIdLoggingContext is only used inside NH calls, and since
-		/// NH calls are never async, this isn't an issue for us.
+		/// NH calls are either async-await or fully synchronous, this isn't an issue for us.
 		/// In addition to that, attempting to match to the current context has proven to be performance hit.
 		/// </summary>
 		public static Guid? SessionId
 		{
-			get { return CurrentSessionId; }
-			set { CurrentSessionId = value; }
+			get => _currentSessionId.Value;
+			set => _currentSessionId.Value = value;
 		}
 
 		#region IDisposable Members
 
 		public void Dispose()
 		{
-			SessionId = oldSessonId;
+			SessionId = _oldSessonId;
 		}
 
 		#endregion