Fix possible thread-safety issue with delayed entity inserts (#2233)

Author: bahusoid

src/NHibernate/Action/DelayedPostInsertIdentifier.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 
 namespace NHibernate.Action
 {
@@ -15,20 +16,12 @@ namespace NHibernate.Action
 	[Serializable]
 	public class DelayedPostInsertIdentifier
 	{
-		[ThreadStatic]
-		private static long _Sequence = 0;
+		private static long GlobalSequence = 0;
 		private readonly long sequence;
 
 		public DelayedPostInsertIdentifier()
 		{
-			lock (typeof(DelayedPostInsertIdentifier))
-			{
-				if (_Sequence == long.MaxValue)
-				{
-					_Sequence = 0;
-				}
-				sequence = _Sequence++;
-			}
+			sequence = Interlocked.Increment(ref GlobalSequence);
 		}
 
 		public override bool Equals(object obj)

src/NHibernate/Action/EntityIdentityInsertAction.cs

@@ -9,7 +9,6 @@ namespace NHibernate.Action
 	[Serializable]
 	public sealed partial class EntityIdentityInsertAction : AbstractEntityInsertAction
 	{
-		private readonly object lockObject = new object();
 		private readonly bool isDelayed;
 		private readonly EntityKey delayedEntityKey;
 		//private CacheEntry cacheEntry;
@@ -19,7 +18,9 @@ public EntityIdentityInsertAction(object[] state, object instance, IEntityPersis
 			: base(null, state, instance, persister, session)
 		{
 			this.isDelayed = isDelayed;
-			delayedEntityKey = this.isDelayed ? GenerateDelayedEntityKey() : null;
+			delayedEntityKey = this.isDelayed
+				? Session.GenerateEntityKey(new DelayedPostInsertIdentifier(), Persister)
+				: null;
 		}
 
 		public object GeneratedId
@@ -32,17 +33,6 @@ public EntityKey DelayedEntityKey
 			get { return delayedEntityKey; }
 		}
 
-		private EntityKey GenerateDelayedEntityKey()
-		{
-			lock (lockObject)
-			{
-				if (!isDelayed)
-					throw new HibernateException("Cannot request delayed entity-key for non-delayed post-insert-id generation");
-
-				return Session.GenerateEntityKey(new DelayedPostInsertIdentifier(), Persister);
-			}
-		}
-
 		protected internal override bool HasPostCommitEventListeners
 		{
 			get