Begin synchronization optimizations

Quite crappy but at least do not rebuild exchange info for each synchronization

src/mesh/ItemValueSynchronizer.hpp

@@ -8,6 +8,51 @@
 
 class ItemValueSynchronizer
 {
+  template <ItemType item_type>
+  using ExchangeItemTypeInfo = std::vector<Array<const ItemIdT<item_type>>>;
+
+  ExchangeItemTypeInfo<ItemType::cell> m_requested_cell_info;
+  ExchangeItemTypeInfo<ItemType::cell> m_provided_cell_info;
+
+  ExchangeItemTypeInfo<ItemType::face> m_requested_face_info;
+  ExchangeItemTypeInfo<ItemType::face> m_provided_face_info;
+
+  ExchangeItemTypeInfo<ItemType::edge> m_requested_edge_info;
+  ExchangeItemTypeInfo<ItemType::edge> m_provided_edge_info;
+
+  ExchangeItemTypeInfo<ItemType::node> m_requested_node_info;
+  ExchangeItemTypeInfo<ItemType::node> m_provided_node_info;
+
+  template <ItemType item_type>
+  PASTIS_INLINE
+  constexpr auto& _getRequestedItemInfo()
+  {
+    if constexpr (item_type == ItemType::cell) {
+      return m_requested_cell_info;
+    } else if constexpr (item_type == ItemType::face) {
+      return m_requested_face_info;
+    } else if constexpr (item_type == ItemType::edge) {
+      return m_requested_edge_info;
+    } else if constexpr (item_type == ItemType::node) {
+      return m_requested_node_info;
+    }
+  }
+
+  template <ItemType item_type>
+  PASTIS_INLINE
+  constexpr auto& _getProvidedItemInfo()
+  {
+    if constexpr (item_type == ItemType::cell) {
+      return m_provided_cell_info;
+    } else if constexpr (item_type == ItemType::face) {
+      return m_provided_face_info;
+    } else if constexpr (item_type == ItemType::edge) {
+      return m_provided_edge_info;
+    } else if constexpr (item_type == ItemType::node) {
+      return m_provided_node_info;
+    }
+  }
+
   template <typename ConnectivityType,
             typename DataType,
             ItemType item_type,
@@ -23,7 +68,14 @@ class ItemValueSynchronizer
 
     const auto& item_owner =  connectivity.template owner<item_type>();
 
-    std::vector<Array<const ItemId>> ghost_items_per_proc
+    auto& ghost_items_per_proc = this->_getRequestedItemInfo<item_type>();
+    auto& to_send_item_id_list_by_proc = this->_getProvidedItemInfo<item_type>();
+
+    Assert(ghost_items_per_proc.size() == to_send_item_id_list_by_proc.size());
+
+    if (ghost_items_per_proc.size() == 0) {
+      pout() << "... building synchronization info\n";
+      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) {
@@ -70,6 +122,8 @@ class ItemValueSynchronizer
         item_number_to_id_correspondance[item_number[item_id]] = item_id;
       }
 
+      to_send_item_id_list_by_proc
+          = [&] () {
               std::vector<Array<const ItemId>> to_send_item_id_list_by_proc(parallel::size());
               for (size_t i_rank=0; i_rank<parallel::size(); ++i_rank) {
                 Array<ItemId> to_send_item_id{local_number_of_values_to_send[i_rank]};
@@ -79,11 +133,14 @@ class ItemValueSynchronizer
                 }
                 to_send_item_id_list_by_proc[i_rank] = to_send_item_id;
               }
+              return to_send_item_id_list_by_proc;
+            } ();
+    }
 
     std::vector<Array<const DataType>> to_send_data_by_proc(parallel::size());
     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];
+      Array<DataType> to_send_data{to_send_item_id.size()};
       parallel_for(to_send_item_id.size(), PASTIS_LAMBDA(size_t i) {
           to_send_data[i] = item_value[to_send_item_id[i]];
         });
@@ -115,9 +172,6 @@ class ItemValueSynchronizer
   PASTIS_INLINE
   void synchronize(ItemValue<DataType, item_type, ConnectivityPtr>& item_value)
   {
-    static int cpt=0;
-    pout() << "Calling synchronize(" << cpt++ << ")...\n";
-
     Assert(item_value.connectivity_ptr().use_count()>0, "No connectivity is associated to this ItemValue");
     const IConnectivity& connectivity = *item_value.connectivity_ptr();
 

src/mesh/ItemValueUtils.hpp

@@ -300,7 +300,7 @@ void synchronize(ItemValue<DataType, item_type, ConnectivityPtr>& item_value)
 {
   static_assert(not std::is_const_v<DataType>, "cannot synchronize ItemValue of const data");
   if (parallel::size() > 1) {
-    ItemValueSynchronizer synchronizer;
+    static ItemValueSynchronizer synchronizer;
     synchronizer.synchronize(item_value);
   }
 }