offset namespace ids

content/browser/dom_storage/dom_storage_context_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_IMPL_H_
 #define CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_IMPL_H_
 
 #include <map>
 #include <set>
 #include <vector>
@@ skipping 129 matching lines @@
   void NotifyItemRemoved(
       const DOMStorageArea* area,
       const base::string16& key,
       const base::string16& old_value,
       const GURL& page_url);
   void NotifyAreaCleared(
       const DOMStorageArea* area,
       const GURL& page_url);
 
   // May be called on any thread.
-  int64 AllocateSessionId() {
-    return session_id_sequence_.GetNext();
-  }
-
+  int64 AllocateSessionId();
   std::string AllocatePersistentSessionId();
 
   // Must be called on the background thread.
   void CreateSessionNamespace(int64 namespace_id,
                               const std::string& persistent_namespace_id);
   void DeleteSessionNamespace(int64 namespace_id, bool should_persist_data);
   void CloneSessionNamespace(int64 existing_id, int64 new_id,
                              const std::string& new_persistent_id);
 
   // Starts backing sessionStorage on disk. This function must be called right
@@ skipping 36 matching lines @@
   base::FilePath sessionstorage_directory_;
 
   // Used to schedule sequenced background tasks.
   scoped_refptr<DOMStorageTaskRunner> task_runner_;
 
   // List of objects observing local storage events.
   ObserverList<EventObserver> event_observers_;
 
   // We use a 32 bit identifier for per tab storage sessions.
   // At a tab per second, this range is large enough for 68 years.
+  // The offset is to more quickly detect the error condition where
+  // an id related to one context is mistakenly used in another.
   base::AtomicSequenceNumber session_id_sequence_;
+  const int session_id_offset_;
 
   bool is_shutdown_;
   bool force_keep_session_state_;
   scoped_refptr<storage::SpecialStoragePolicy> special_storage_policy_;
   scoped_refptr<SessionStorageDatabase> session_storage_database_;
 
   // For cleaning up unused namespaces gradually.
   bool scavenging_started_;
   std::vector<std::string> deletable_persistent_namespace_ids_;
 
   // Persistent namespace IDs to protect from gradual deletion (they will
   // be needed for session restore).
   std::set<std::string> protected_persistent_session_ids_;
 
   // Mapping between persistent namespace IDs and namespace IDs for
   // sessionStorage.
   std::map<std::string, int64> persistent_namespace_id_to_namespace_id_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_IMPL_H_