Implement token promotion to session when it is necessary

- promotion from transaction to session
- session tokens expiry
- no session token when it is not needed

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Session.Transactions.cs

@@ -5,6 +5,7 @@
 // Created:    2008.11.07
 
 using System;
+using System.Collections.Generic;
 using System.Transactions;
 using Xtensive.Orm.Configuration;
 using Xtensive.Orm.Internals;
@@ -18,7 +19,8 @@ public partial class Session
   {
     private const string SavepointNameFormat = "s{0}";
 
-    private readonly StateLifetimeToken sessionLifetimeToken = new StateLifetimeToken();
+    private readonly StateLifetimeToken sessionLifetimeToken;
+    private readonly List<StateLifetimeToken> promotedLifetimeTokens;
     private int nextSavepoint;
 
     /// <summary>
@@ -338,5 +340,14 @@ internal StateLifetimeToken GetLifetimeToken()
         return sessionLifetimeToken;
       throw new InvalidOperationException(Strings.ExActiveTransactionIsRequiredForThisOperationUseSessionOpenTransactionToOpenIt);
     }
+
+    internal bool TryPromoteTokens(IEnumerable<StateLifetimeToken> tokens)
+    {
+      if (promotedLifetimeTokens is null) {
+        return false;
+      }
+      promotedLifetimeTokens.AddRange(tokens);
+      return true;
+    }
   }
 }

Orm/Xtensive.Orm/Orm/Session.cs

@@ -589,6 +589,10 @@ internal Session(Domain domain, StorageNode selectedStorageNode, SessionConfigur
       remapper = new KeyRemapper(this);
 
       disableAutoSaveChanges = !configuration.Supports(SessionOptions.AutoSaveChanges);
+      if (configuration.Supports(SessionOptions.NonTransactionalReads)) {
+        promotedLifetimeTokens = new List<StateLifetimeToken>();
+        sessionLifetimeToken = new StateLifetimeToken();
+      }
 
       // Perform activation
       if (activate) {
@@ -613,6 +617,13 @@ public void Dispose()
           OrmLog.Debug(Strings.LogSessionXDisposing, this);
         }
 
+        sessionLifetimeToken?.Expire();
+        if (promotedLifetimeTokens?.Count > 0) {
+          foreach (var token in promotedLifetimeTokens) {
+            token.Expire();
+          }
+        }
+
         SystemEvents.NotifyDisposing();
         Events.NotifyDisposing();
 

Orm/Xtensive.Orm/Orm/Transaction.cs

@@ -6,6 +6,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Transactions;
 using JetBrains.Annotations;
 using Xtensive.Collections;
@@ -188,10 +189,10 @@ internal void Commit()
         Rollback();
         throw;
       }
-      if (Outer!=null)
+      if (Outer != null)
         PromoteLifetimeTokens();
       else if (Session.Configuration.Supports(SessionOptions.NonTransactionalReads))
-        ClearLifetimeTokens();
+        PromoteLifetimeTokensToSession();
       else
         ExpireLifetimeTokens();
       State = TransactionState.Committed;
@@ -244,6 +245,15 @@ private void PromoteLifetimeTokens()
       ClearLifetimeTokens();
     }
 
+    private void PromoteLifetimeTokensToSession()
+    {
+      if (Outer != null
+          || !Session.TryPromoteTokens(EnumerableUtils.One(LifetimeToken).Union(lifetimeTokens))) {
+        throw new InvalidOperationException("Promoting to session is not supported.");
+      }
+      ClearLifetimeTokens();
+    }
+
     private void ClearLifetimeTokens()
     {
       lifetimeTokens.Clear();