Index: include/mapnik/timer.hpp
===================================================================
--- include/mapnik/timer.hpp	(revision 3246)
+++ include/mapnik/timer.hpp	(working copy)
@@ -40,14 +40,14 @@

     void restart()
     {
-        _wall_clock_end = NULL;
-        _cpu_end = NULL;
+        //_wall_clock_end = NULL;
+        //_cpu_end = NULL;

         gettimeofday(&_wall_clock_start, NULL);
         _cpu_start = clock();
     }

-    virtual void stop()
+    virtual void stop() const
     {
         _cpu_end = clock();
         gettimeofday(&_wall_clock_end, NULL);
@@ -65,8 +65,8 @@
     double wall_clock_elapsed() const
     {
         // return elapsed wall clock time in ms
-        if (!_wall_clock_end)
-            stop();
+        //if (!_wall_clock_end)
+        //    stop();

         long seconds  = _wall_clock_end.tv_sec  - _wall_clock_start.tv_sec;
         long useconds = _wall_clock_end.tv_usec - _wall_clock_start.tv_usec;
@@ -74,8 +74,8 @@
         return ((seconds) * 1000 + useconds / 1000.0) + 0.5;
     }
 private:
-    timeval _wall_clock_start, _wall_clock_end;
-    clock_t _cpu_start, _cpu_end;
+    mutable timeval _wall_clock_start, _wall_clock_end;
+    mutable clock_t _cpu_start, _cpu_end;
 };

 //  A progress_timer behaves like a timer except that the destructor displays
@@ -94,7 +94,8 @@
             stop();
     }

-    void stop() {
+    void stop() const
+    {
         timer::stop();

         stopped_ = true;
@@ -103,7 +104,7 @@
             std::ostringstream s;
             s.precision(2);
             s << std::fixed;
-            s << wall_clock_elapsed() << "ms (cpu " << cpu_elapsed() << "ms)"
+            s << wall_clock_elapsed() << "ms (cpu " << cpu_elapsed() << "ms)";
             s << std::setw(30 - (int)s.tellp()) << std::right << "| " << base_message_ << "\n";
             os_ << s.str();
         }
@@ -117,7 +118,7 @@
 private:
     std::ostream & os_;
     std::string base_message_;
-    bool stopped_;
+    mutable bool stopped_;
 };

 };