FeaturesOffsets table onload building

indexer/features_offsets_table.cpp

@@ -1,5 +1,7 @@
 #include "features_offsets_table.hpp"
 
+#include "../indexer/data_header.hpp"
+#include "../indexer/features_vector.hpp"
 #include "../coding/file_writer.hpp"
 #include "../base/assert.hpp"
 #include "../base/scope_guard.hpp"
@@ -50,6 +52,31 @@ namespace feature
     return unique_ptr<FeaturesOffsetsTable>(new FeaturesOffsetsTable(std::move(handle)));
   }
 
+  // static
+  unique_ptr<FeaturesOffsetsTable> FeaturesOffsetsTable::CreateIfNotExistsAndLoad(
+      FilesMappingContainer const & container)
+  {
+    if (container.IsExist(FEATURES_OFFSETS_TABLE_FILE_TAG))
+      return Load(container);
+
+    if (!container.IsExist(HEADER_FILE_TAG))
+      return unique_ptr<FeaturesOffsetsTable>();
+
+    FilesContainerR cont(container.GetName());
+    DataHeader header;
+    header.Load(cont.GetReader(HEADER_FILE_TAG));
+
+    Builder builder;
+    FeaturesVector(cont, header).ForEachOffset([&builder] (FeatureType const &, uint32_t offset)
+    {
+      builder.PushOffset(offset);
+    });
+    unique_ptr<FeaturesOffsetsTable> table(Build(builder));
+    FilesContainerW writeCont(container.GetName(), FileWriter::OP_WRITE_EXISTING);
+    table->Save(writeCont);
+    return table;
+  }
+
   void FeaturesOffsetsTable::Save(FilesContainerW & container)
   {
     string const fileName = container.GetFileName() + "." FEATURES_OFFSETS_TABLE_FILE_TAG;

indexer/features_offsets_table.hpp

@@ -57,6 +57,21 @@ namespace feature
     ///         when it's not possible to load FeaturesOffsetsTable.
     static unique_ptr<FeaturesOffsetsTable> Load(FilesMappingContainer const & container);
 
+    /// Loads FeaturesOffsetsTable from FilesMappingContainer. Note
+    /// that some part of a file referenced by container will be
+    /// mapped to the memory and used by internal structures of
+    /// FeaturesOffsetsTable.
+    /// If there is no FeaturesOffsetsTable section in the container,
+    /// the function builds it from section devoted to features.
+    ///
+    /// \warning May take a lot of time if there is no precomputed section
+    ///
+    /// \param container a container with a section devoted to
+    ///                  FeaturesOffsetsTable
+    /// \return a pointer to an instance of FeaturesOffsetsTable or nullptr
+    ///         when it's not possible to create FeaturesOffsetsTable.
+    static unique_ptr<FeaturesOffsetsTable> CreateIfNotExistsAndLoad(FilesMappingContainer const & container);
+
     FeaturesOffsetsTable(FeaturesOffsetsTable const &) = delete;
     FeaturesOffsetsTable const & operator=(FeaturesOffsetsTable const &) = delete;
 

indexer/indexer_tests/features_offsets_table_test.cpp

@@ -47,6 +47,27 @@ namespace feature
     TEST_EQUAL(static_cast<uint64_t>(1024), table->GetFeatureOffset(7), ());
   }
 
+  UNIT_TEST(FeaturesOffsetsTable_CreateIfNotExistsAndLoad)
+  {
+    Platform & p = GetPlatform();
+    FilesContainerR baseContainer(p.GetReader("minsk-pass" DATA_FILE_EXTENSION));
+    if (baseContainer.IsExist(FEATURES_OFFSETS_TABLE_FILE_TAG))
+      FilesContainerW(baseContainer.GetFileName(), FileWriter::OP_WRITE_EXISTING).DeleteSection(FEATURES_OFFSETS_TABLE_FILE_TAG);
+    FilesMappingContainer mappingContainer(baseContainer.GetFileName());
+    unique_ptr<FeaturesOffsetsTable> table(FeaturesOffsetsTable::CreateIfNotExistsAndLoad(mappingContainer));
+    TEST(table.get(), ());
+
+    feature::DataHeader header;
+    header.Load(baseContainer.GetReader(HEADER_FILE_TAG));
+
+    uint64_t builderSize = 0;
+    FeaturesVector(baseContainer, header).ForEachOffset([&builderSize](FeatureType const & /* type */, uint64_t)
+    {
+      ++builderSize;
+    });
+    TEST_EQUAL(builderSize, table->size(), ());
+  }
+
   UNIT_TEST(FeaturesOffsetsTable_ReadWrite)
   {
     Platform & p = GetPlatform();
@@ -55,10 +76,8 @@ namespace feature
     feature::DataHeader header;
     header.Load(baseContainer.GetReader(HEADER_FILE_TAG));
 
-    FeaturesVector features(baseContainer, header);
-
     FeaturesOffsetsTable::Builder builder;
-    features.ForEachOffset([&builder](FeatureType /* type */, uint64_t offset)
+    FeaturesVector(baseContainer, header).ForEachOffset([&builder](FeatureType const & /* type */, uint64_t offset)
                            {
                              builder.PushOffset(offset);
                            });