Use few parallel_for instead of standard for

This is mainly cosmetic. Performances issue are related to the recalculation of
synchronization info.

src/mesh/ItemValueSynchronizer.hpp

@@ -4,7 +4,7 @@
 #include <ItemValue.hpp>
 #include <Connectivity.hpp>
 
-#include <unordered_map>
+#include <map>
 
 class ItemValueSynchronizer
 {
@@ -18,15 +18,26 @@ class ItemValueSynchronizer
   {
     static_assert(not std::is_abstract_v<ConnectivityType>,
                   "_synchronize must be called on a concrete connectivity");
-    const auto& item_owner =  connectivity.template owner<item_type>();
 
     using ItemId = ItemIdT<item_type>;
-    std::vector<std::vector<ItemId>> ghost_items_per_proc(parallel::size());
+
+    const auto& item_owner =  connectivity.template owner<item_type>();
+
+    std::vector<Array<const ItemId>> ghost_items_per_proc
+        = [&] () {
+            std::vector<std::vector<ItemId>> ghost_items_vector_per_proc(parallel::size());
             for (ItemId item_id=0; item_id<item_value.size(); ++item_id) {
               if (const size_t owner = item_owner[item_id]; owner != parallel::rank()) {
-        ghost_items_per_proc[owner].emplace_back(item_id);
+                ghost_items_vector_per_proc[owner].emplace_back(item_id);
               }
             }
+            std::vector<Array<const ItemId>> ghost_items_per_proc(parallel::size());
+            for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
+              const auto& ghost_items_vector = ghost_items_vector_per_proc[i_rank];
+              ghost_items_per_proc[i_rank] = convert_to_array(ghost_items_vector);
+            }
+            return ghost_items_per_proc;
+          }();
 
     Array<unsigned int> local_number_of_requested_values(parallel::size());
     for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
@@ -41,9 +52,9 @@ class ItemValueSynchronizer
     for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
       const auto& ghost_items = ghost_items_per_proc[i_rank];
       Array<int> item_number_list(ghost_items.size());
-      for (size_t i_item = 0; i_item<ghost_items.size(); ++i_item) {
+      parallel_for (ghost_items.size(), PASTIS_LAMBDA(size_t i_item) {
           item_number_list[i_item] = item_number[ghost_items[i_item]];
-      }
+        });
       requested_item_number_list_by_proc[i_rank] = item_number_list;
     }
 
@@ -54,7 +65,7 @@ class ItemValueSynchronizer
 
     parallel::exchange(requested_item_number_list_by_proc, to_send_item_number_list_by_proc);
 
-    std::unordered_map<int, ItemId> item_number_to_id_correspondance(connectivity.template numberOf<item_type>());
+    std::map<int, ItemId> item_number_to_id_correspondance;
     for (ItemId item_id=0; item_id<item_number.size(); ++item_id) {
       item_number_to_id_correspondance[item_number[item_id]] = item_id;
     }
@@ -64,7 +75,7 @@ class ItemValueSynchronizer
       Array<ItemId> to_send_item_id{local_number_of_values_to_send[i_rank]};
       const Array<int>& to_send_item_number = to_send_item_number_list_by_proc[i_rank];
       for (size_t i=0; i<to_send_item_number.size(); ++i) {
-        to_send_item_id[i] = item_number_to_id_correspondance[to_send_item_number[i]];
+        to_send_item_id[i] = item_number_to_id_correspondance.find(to_send_item_number[i])->second;
       }
       to_send_item_id_list_by_proc[i_rank] = to_send_item_id;
     }
@@ -73,9 +84,9 @@ class ItemValueSynchronizer
     for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
       Array<DataType> to_send_data{local_number_of_values_to_send[i_rank]};
       const Array<const ItemId>& to_send_item_id = to_send_item_id_list_by_proc[i_rank];
-      for (size_t i=0; i<to_send_item_id.size(); ++i) {
+      parallel_for(to_send_item_id.size(), PASTIS_LAMBDA(size_t i) {
           to_send_data[i] = item_value[to_send_item_id[i]];
-      }
+        });
       to_send_data_by_proc[i_rank] = to_send_data;
     }
 
@@ -90,9 +101,9 @@ class ItemValueSynchronizer
     for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
       const auto& ghost_items = ghost_items_per_proc[i_rank];
       const auto& requested_data = requested_data_list_by_proc[i_rank];
-      for (size_t i=0; i<ghost_items.size(); ++i) {
+      parallel_for(ghost_items.size(), PASTIS_LAMBDA(size_t i) {
           item_value[ghost_items[i]] = requested_data[i];
-      }
+        });
       requested_data_list_by_proc[i_rank] = Array<DataType>{ghost_items.size()};
     }
   }