block refresh until the last context has finished execution

shared_realm.cpp

@@ -287,8 +287,6 @@ void Realm::cancel_transaction()
 void Realm::invalidate()
 {
     verify_thread();
-    check_read_write(this);
-
     if (m_in_transaction) {
         cancel_transaction();
     }
@@ -384,6 +382,10 @@ void Realm::close()
         m_notifier->remove_realm(this);
     }
 
+    if (m_group) {
+        m_shared_group->end_read();
+    }
+
     m_group = nullptr;
     m_shared_group = nullptr;
     m_history = nullptr;

shared_realm.hpp

@@ -197,6 +197,12 @@ namespace realm {
       public:
         UnitializedRealmException(std::string message) : std::runtime_error(message) {}
     };
+
+    class ClosedRealmException : public std::runtime_error
+    {
+      public:
+        ClosedRealmException(std::string message) : std::runtime_error(message) {}
+    };
 }
 
 #endif /* defined(REALM_REALM_HPP) */