Short-Circuit SessionFactoryImpl.Close() when already closed (#2223)

Author: albertodall

src/NHibernate/Async/Impl/SessionFactoryImpl.cs

@@ -63,6 +63,16 @@ public sealed partial class SessionFactoryImpl : ISessionFactoryImplementor, IOb
 		public async Task CloseAsync(CancellationToken cancellationToken = default(CancellationToken))
 		{
 			cancellationToken.ThrowIfCancellationRequested();
+			if (isClosed)
+			{
+				if (log.IsDebugEnabled())
+				{
+					log.Debug("Already closed");
+				}
+
+				return;
+			}
+
 			log.Info("Closing");
 
 			isClosed = true;

src/NHibernate/Impl/SessionFactoryImpl.cs

@@ -857,6 +857,16 @@ public void Dispose()
 		/// </summary>
 		public void Close()
 		{
+			if (isClosed)
+			{
+				if (log.IsDebugEnabled())
+				{
+					log.Debug("Already closed");
+				}
+
+				return;
+			}
+
 			log.Info("Closing");
 
 			isClosed = true;