attaching schema nodes progress

include/matador/logger/log_domain.hpp

@@ -93,7 +93,7 @@ public:
    * @param source Source of the log message
    * @param message Message to log
    */
-  void log(log_level lvl, const std::string &source, const char *message);
+  void log(log_level lvl, const std::string &source, const char *message) const;
 
   /**
    * Clears the list of log sinks
@@ -101,7 +101,7 @@ public:
   void clear();
 
 private:
-  void get_time_stamp(char* timestamp_buffer);
+  void get_time_stamp(char* timestamp_buffer) const;
 
 private:
   static std::map<log_level, std::string> level_strings;
@@ -111,7 +111,7 @@ private:
 
   log_level_range log_level_range_;
 
-  std::mutex mutex_;
+  mutable std::mutex mutex_;
 };
 
 }