Simplify expire tree merging

This also fixes a (theoretical) bug introduced a bit earlier when clones
were only generated for outputs that need forward depencencies. In that
case the outputs and clones used in merging expire trees did not match.
The bug is theoretical, because there is currently no way in osm2pgsql
to create several outputs of which some need dependency management and
others don't.

Author: joto

src/osmdata.cpp

@@ -186,7 +186,9 @@ struct pending_threaded_processor : public pending_processor
     {
         while (osmid_t const id = pop_id(queue, mutex)) {
             for (auto const &output : outputs) {
-                output->pending_way(id);
+                if (output) {
+                    output->pending_way(id);
+                }
             }
         }
     }
@@ -196,7 +198,9 @@ struct pending_threaded_processor : public pending_processor
     {
         while (osmid_t const id = pop_id(queue, mutex)) {
             for (auto const &output : outputs) {
-                output->pending_relation(id);
+                if (output) {
+                    output->pending_relation(id);
+                }
             }
         }
     }
@@ -237,6 +241,8 @@ struct pending_threaded_processor : public pending_processor
             for (auto const &out : m_outputs) {
                 if (out->need_forward_dependencies()) {
                     m_clones[i].push_back(out->clone(midq, copy_thread));
+                } else {
+                    m_clones[i].emplace_back(nullptr);
                 }
             }
         }
@@ -282,7 +288,9 @@ struct pending_threaded_processor : public pending_processor
 
         for (auto const &clone : m_clones) {
             for (auto const &clone_output : clone) {
-                clone_output->commit();
+                if (clone_output) {
+                    clone_output->commit();
+                }
             }
         }
 
@@ -305,16 +313,16 @@ struct pending_threaded_processor : public pending_processor
     {
         process_queue("relation", do_rels);
 
-        //collect all expiry tree informations together into one
+        // Collect expiry tree information from all clones and merge it back
+        // into the original outputs.
         for (auto const &clone : m_clones) {
-            for (output_vec_t::const_iterator
-                     original_output = m_outputs.begin(),
-                     clone_output = clone.begin();
-                 original_output != m_outputs.end() &&
-                 clone_output != clone.end();
-                 ++original_output, ++clone_output) {
-                //merge the expire tree from this threads copy of output back
-                original_output->get()->merge_expire_trees(clone_output->get());
+            auto it = clone.begin();
+            for (auto const &output : m_outputs) {
+                assert(it != clone.end());
+                if (*it) {
+                    output->merge_expire_trees(it->get());
+                }
+                ++it;
             }
         }
     }