[consider merging] Enabling Shapes-based RecursiveShapeIterators for MT-use

This fixes a crash when using DRC fill in tiled mode with multiple
threads.

src/db/db/dbFillTool.cc

@@ -280,7 +280,8 @@ fill_polygon_impl (db::Cell *cell, const db::Polygon &fp0, db::cell_index_type f
 
             {
               //  In case we run this from a tiling processor we need to lock against multithread races
-              tl::MutexLocker locker (&db::TilingProcessor::output_lock ());
+              tl_assert (cell->layout () != 0);
+              tl::MutexLocker locker (&cell->layout ()->lock ());
               cell->insert (array);
             }
 

src/db/db/dbRecursiveShapeIterator.cc

@@ -500,15 +500,21 @@ RecursiveShapeIterator::validate (RecursiveShapeReceiver *receiver) const
   }
 
   if (mp_shapes) {
+
     //  Ensures the trees are built properly - this is important in MT contexts (i.e. TilingProcessor)
     //  TODO: get rid of that const cast
     (const_cast <db::Shapes *> (mp_shapes))->update ();
+
     start_shapes ();
+
   } else if (mp_layout && (! m_has_layers || m_current_layer < m_layers.size ())) {
+
     //  Ensures the trees are built properly - this is important in MT contexts (i.e. TilingProcessor)
     mp_layout->update ();
+
     new_cell (receiver);
     next_shape (receiver);
+
   }
 
   if (mp_layout && ! at_end ()) {

src/db/db/dbShapes.cc

@@ -1127,10 +1127,20 @@ void Shapes::reset_bbox_dirty ()
 
 void Shapes::update ()
 {
+  std::unique_ptr<tl::MutexLocker> locker;
+
+  //  If not in a layout context, we should lock here against multiple calls from different threads.
+  //  In a layout context, the Layout object will do that for us.
+  if (layout () == 0) {
+    static tl::Mutex lock;
+    locker.reset (new tl::MutexLocker (&lock));
+  }
+
   for (tl::vector<LayerBase *>::const_iterator l = m_layers.begin (); l != m_layers.end (); ++l) {
     (*l)->sort ();
     (*l)->update_bbox ();
   }
+
   set_dirty (false);
 }