[Serving][Refactor] Major codebase refactor

This PR is a major refactor of the serving framework.
It contains the following aspects:

* Changing Model and Sampler from `runtime.Module` to Object
in TVM. Exposing the public interface through public member
function (rather than through `GetFunction` which returns PackedFunc).
Separating the definition and implementation of Model/Sampler
classes. Now a base Model/Sampler class definition is in their
respective header files, and the implementations are in .cc files.
* Removing the TokenizerModule class, and directly using the
Tokenizer class in `tokenizer_cpp`, to reduce indirection.
* Introducing unique string `id` to Request. This id is passed
in from frontend as a Request constructor parameter, and is the
unique identifier of a request.
* Reducing the uses of `ShapeTuple` after the Model/Sampler/Tokenizer
interface changes.
* Moving some previous member functions in Engine (such as "getting
data length", "getting data embedding") to the corresponding
data structure side.
* Introducing struct `EngineStats` to contain all the runtime
statistics of the engine.
* Classifying and reordering the member functions in Engine.

cpp/serve/data.cc

@@ -6,6 +6,8 @@
 
 #include <tvm/runtime/registry.h>
 
+#include "model.h"
+
 namespace mlc {
 namespace llm {
 namespace serve {
@@ -24,6 +26,16 @@ TextData::TextData(String text) {
   data_ = std::move(n);
 }
 
+int TextDataNode::GetLength() const {
+  LOG(FATAL) << "\"GetLength\" for TextData is not supported. "
+                "Please tokenize the text and construct a TokenData object.";
+}
+
+NDArray TextDataNode::GetEmbedding(Model model) const {
+  LOG(FATAL) << "\"GetEmbedding\" for TextData is not supported. "
+                "Please tokenize the text and construct a TokenData object.";
+}
+
 TVM_REGISTER_GLOBAL("mlc.serve.TextData").set_body_typed([](String text) {
   return TextData(std::move(text));
 });
@@ -36,18 +48,22 @@ TVM_REGISTER_GLOBAL("mlc.serve.TextDataGetTextString").set_body_typed([](TextDat
 
 TVM_REGISTER_OBJECT_TYPE(TokenDataNode);
 
-TokenData::TokenData(ShapeTuple token_ids) {
+TokenData::TokenData(IntTuple token_ids) {
   ObjectPtr<TokenDataNode> n = make_object<TokenDataNode>();
   n->token_ids = std::move(token_ids);
   data_ = std::move(n);
 }
 
 TokenData::TokenData(std::vector<int32_t> token_ids) {
   ObjectPtr<TokenDataNode> n = make_object<TokenDataNode>();
-  n->token_ids = ShapeTuple(token_ids.begin(), token_ids.end());
+  n->token_ids = IntTuple(token_ids.begin(), token_ids.end());
   data_ = std::move(n);
 }
 
+int TokenDataNode::GetLength() const { return token_ids.size(); }
+
+NDArray TokenDataNode::GetEmbedding(Model model) const { return model->TokenEmbed(token_ids); }
+
 TVM_REGISTER_GLOBAL("mlc.serve.TokenData").set_body([](TVMArgs args, TVMRetValue* rv) {
   std::vector<int32_t> token_ids;
   token_ids.reserve(args.size());

cpp/serve/data.h

@@ -7,6 +7,7 @@
 
 #include <tvm/runtime/container/shape_tuple.h>
 #include <tvm/runtime/container/string.h>
+#include <tvm/runtime/ndarray.h>
 #include <tvm/runtime/object.h>
 
 namespace mlc {
@@ -15,11 +16,19 @@ namespace serve {
 
 using namespace tvm::runtime;
 
+class Model;
+
 /****************** DataNode ******************/
 
 /*! \brief The base class of multi-modality data (text, tokens, embedding, etc). */
 class DataNode : public Object {
  public:
+  /*! \brief Get the length (equivalent number of tokens) of the data. */
+  virtual int GetLength() const = 0;
+
+  /*! \brief Compute the embedding of this data with regard to the input model. */
+  virtual NDArray GetEmbedding(Model model) const = 0;
+
   static constexpr const char* _type_key = "mlc.serve.Data";
   static constexpr const bool _type_has_method_sequal_reduce = false;
   static constexpr const bool _type_has_method_shash_reduce = false;
@@ -39,6 +48,9 @@ class TextDataNode : public DataNode {
   /*! \brief The text string. */
   String text;
 
+  int GetLength() const final;
+  NDArray GetEmbedding(Model model) const final;
+
   static constexpr const char* _type_key = "mlc.serve.TextData";
   TVM_DECLARE_BASE_OBJECT_INFO(TextDataNode, DataNode);
 };
@@ -56,15 +68,18 @@ class TextData : public Data {
 class TokenDataNode : public DataNode {
  public:
   /*! \brief The token ids. */
-  ShapeTuple token_ids;
+  IntTuple token_ids;
+
+  int GetLength() const final;
+  NDArray GetEmbedding(Model model) const final;
 
   static constexpr const char* _type_key = "mlc.serve.TokenData";
   TVM_DECLARE_BASE_OBJECT_INFO(TokenDataNode, DataNode);
 };
 
 class TokenData : public Data {
  public:
-  explicit TokenData(ShapeTuple token_ids);
+  explicit TokenData(IntTuple token_ids);
 
   explicit TokenData(std::vector<int32_t> token_ids);