Use memcpy to copy tables into vectors.

Ideally we wouldn't be copying at all, and somehow cast the table to a vector.
Unfortunately I haven't figured out how to do that, and this solution at least
gets us from 0.065 ms to 0.028 ms in testCreateCommand.

2 files changed, 24 insertions, 10 deletions

diff --git a/common/entitybuffer.cpp b/common/entitybuffer.cpp
index 5ba4afe..b555ac3 100644
--- a/common/entitybuffer.cpp
+++ b/common/entitybuffer.cpp
@@ -56,17 +56,24 @@ void EntityBuffer::extractResourceBuffer(void *dataValue, int dataSize, const st
     }
 }
 
-void EntityBuffer::assembleEntityBuffer(flatbuffers::FlatBufferBuilder &fbb, void const *metadataData, size_t metadataSize, void const *resourceData, size_t resourceSize, void const *localData, size_t localSize)
+flatbuffers::Offset<flatbuffers::Vector<uint8_t> > EntityBuffer::appendAsVector(flatbuffers::FlatBufferBuilder &fbb, void const *data, size_t size)
 {
-    auto metadata = fbb.CreateVector<uint8_t>(static_cast<uint8_t const*>(metadataData), metadataSize);
-    auto resource = fbb.CreateVector<uint8_t>(static_cast<uint8_t const*>(resourceData), resourceSize);
-    auto local = fbb.CreateVector<uint8_t>(static_cast<uint8_t const*>(localData), localSize);
-    auto builder = Akonadi2::EntityBuilder(fbb);
-    builder.add_metadata(metadata);
-    builder.add_resource(resource);
-    builder.add_local(local);
+    //Since we do memcpy trickery, this will only work on little endian
+    assert(FLATBUFFERS_LITTLEENDIAN);
+    auto metadata = fbb.CreateUninitializedVector<uint8_t>(size);
+    {
+        auto ptr = reinterpret_cast<flatbuffers::Vector<uint8_t> *>(fbb.GetBufferPointer())->Data();
+        std::memcpy((void*)ptr, data, size);
+    }
+    return metadata;
+}
 
-    auto buffer = builder.Finish();
-    Akonadi2::FinishEntityBuffer(fbb, buffer);
+void EntityBuffer::assembleEntityBuffer(flatbuffers::FlatBufferBuilder &fbb, void const *metadataData, size_t metadataSize, void const *resourceData, size_t resourceSize, void const *localData, size_t localSize)
+{
+    auto metadata = appendAsVector(fbb, metadataData, metadataSize);
+    auto resource = appendAsVector(fbb, resourceData, resourceSize);
+    auto local = appendAsVector(fbb, localData, localSize);
+    auto entity = Akonadi2::CreateEntity(fbb, metadata, resource, local);
+    Akonadi2::FinishEntityBuffer(fbb, entity);
 }
 
diff --git a/common/entitybuffer.h b/common/entitybuffer.h
index 097b450..f22c84e 100644
--- a/common/entitybuffer.h
+++ b/common/entitybuffer.h
@@ -15,7 +15,14 @@ public:
     const Entity &entity();
 
     static void extractResourceBuffer(void *dataValue, int dataSize, const std::function<void(const uint8_t *, size_t size)> &handler);
+    /*
+     * TODO: Ideally we would be passing references to vectors in the same bufferbuilder, to avoid needlessly copying data.
+     * Unfortunately I couldn't find a way to cast a table to a vector<uint8_t> reference.
+     * We can't use union's either (which would allow to have a field that stores a selection of tables), as we don't want to modify
+     * the entity schema for each resource's buffers.
+     */
     static void assembleEntityBuffer(flatbuffers::FlatBufferBuilder &fbb, void const *metadataData, size_t metadataSize, void const *resourceData, size_t resourceSize, void const *localData, size_t localSize);
+    static flatbuffers::Offset<flatbuffers::Vector<uint8_t> > appendAsVector(flatbuffers::FlatBufferBuilder &fbb, void const *data, size_t size);
 
 private:
     const Entity *mEntity;