gin/function_template.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef GIN_FUNCTION_TEMPLATE_H_
   6 #define GIN_FUNCTION_TEMPLATE_H_
   7
   8 #include "base/callback.h"
   9 #include "base/logging.h"
  10 #include "gin/arguments.h"
  11 #include "gin/converter.h"
  12 #include "gin/gin_export.h"
  13 #include "v8/include/v8.h"
  14
  15 namespace gin {
  16
  17 class PerIsolateData;
  18
  19 enum CreateFunctionTemplateFlags {
  20   HolderIsFirstArgument = 1 << 0,
  21 };
  22
  23 namespace internal {
  24
  25 template<typename T>
  26 struct CallbackParamTraits {
  27   typedef T LocalType;
  28 };
  29 template<typename T>
  30 struct CallbackParamTraits<const T&> {
  31   typedef T LocalType;
  32 };
  33 template<typename T>
  34 struct CallbackParamTraits<const T*> {
  35   typedef T* LocalType;
  36 };
  37
  38
  39 // CallbackHolder and CallbackHolderBase are used to pass a base::Callback from
  40 // CreateFunctionTemplate through v8 (via v8::FunctionTemplate) to
  41 // DispatchToCallback, where it is invoked.
  42
  43 // This simple base class is used so that we can share a single object template
  44 // among every CallbackHolder instance.
  45 class GIN_EXPORT CallbackHolderBase {
  46  public:
  47   v8::Handle<v8::External> GetHandle(v8::Isolate* isolate);
  48
  49  protected:
  50   explicit CallbackHolderBase(v8::Isolate* isolate);
  51   virtual ~CallbackHolderBase();
  52
  53  private:
  54   static void WeakCallback(
  55       const v8::WeakCallbackData<v8::External, CallbackHolderBase>& data);
  56
  57   v8::Persistent<v8::External> v8_ref_;
  58
  59   DISALLOW_COPY_AND_ASSIGN(CallbackHolderBase);
  60 };
  61
  62 template<typename Sig>
  63 class CallbackHolder : public CallbackHolderBase {
  64  public:
  65   CallbackHolder(v8::Isolate* isolate,
  66                  const base::Callback<Sig>& callback,
  67                  int flags)
  68       : CallbackHolderBase(isolate), callback(callback), flags(flags) {}
  69   base::Callback<Sig> callback;
  70   int flags;
  71  private:
  72   virtual ~CallbackHolder() {}
  73
  74   DISALLOW_COPY_AND_ASSIGN(CallbackHolder);
  75 };
  76
  77 template<typename T>
  78 bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
  79                      T* result) {
  80   if (is_first && (create_flags & HolderIsFirstArgument) != 0) {
  81     return args->GetHolder(result);
  82   } else {
  83     return args->GetNext(result);
  84   }
  85 }
  86
  87 // For advanced use cases, we allow callers to request the unparsed Arguments
  88 // object and poke around in it directly.
  89 inline bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
  90                             Arguments* result) {
  91   *result = *args;
  92   return true;
  93 }
  94 inline bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
  95                             Arguments** result) {
  96   *result = args;
  97   return true;
  98 }
  99
 100 // It's common for clients to just need the isolate, so we make that easy.
 101 inline bool GetNextArgument(Arguments* args, int create_flags,
 102                             bool is_first, v8::Isolate** result) {
 103   *result = args->isolate();
 104   return true;
 105 }
 106
 107 // Classes for generating and storing an argument pack of integer indices
 108 // (based on well-known "indices trick", see: http://goo.gl/bKKojn):
 109 template <size_t... indices>
 110 struct IndicesHolder {};
 111
 112 template <size_t requested_index, size_t... indices>
 113 struct IndicesGenerator {
 114   using type = typename IndicesGenerator<requested_index - 1,
 115                                          requested_index - 1,
 116                                          indices...>::type;
 117 };
 118 template <size_t... indices>
 119 struct IndicesGenerator<0, indices...> {
 120   using type = IndicesHolder<indices...>;
 121 };
 122
 123 // Class template for extracting and storing single argument for callback
 124 // at position |index|.
 125 template <size_t index, typename ArgType>
 126 struct ArgumentHolder {
 127   using ArgLocalType = typename CallbackParamTraits<ArgType>::LocalType;
 128
 129   ArgLocalType value;
 130   bool ok;
 131
 132   ArgumentHolder(Arguments* args, int create_flags)
 133       : ok(GetNextArgument(args, create_flags, index == 0, &value)) {
 134     if (!ok)
 135       args->ThrowError();
 136   }
 137 };
 138
 139 // Class template for converting arguments from JavaScript to C++ and running
 140 // the callback with them.
 141 template <typename IndicesType, typename... ArgTypes>
 142 class Invoker {};
 143
 144 template <size_t... indices, typename... ArgTypes>
 145 class Invoker<IndicesHolder<indices...>, ArgTypes...>
 146     : public ArgumentHolder<indices, ArgTypes>... {
 147  public:
 148   // Invoker<> inherits from ArgumentHolder<> for each argument.
 149   // C++ has always been strict about the class initialization order,
 150   // so it is guaranteed ArgumentHolders will be initialized (and thus, will
 151   // extract arguments from Arguments) in the right order.
 152   Invoker(Arguments* args, int create_flags)
 153       : ArgumentHolder<indices, ArgTypes>(args, create_flags)..., args_(args) {
 154     // GCC thinks that create_flags is going unused, even though the
 155     // expansion above clearly makes use of it. Per jyasskin@, casting
 156     // to void is the commonly accepted way to convince the compiler
 157     // that you're actually using a parameter/varible.
 158     (void)create_flags;
 159   }
 160
 161   bool IsOK() {
 162     return And(ArgumentHolder<indices, ArgTypes>::ok...);
 163   }
 164
 165   template <typename ReturnType>
 166   void DispatchToCallback(base::Callback<ReturnType(ArgTypes...)> callback) {
 167     args_->Return(callback.Run(ArgumentHolder<indices, ArgTypes>::value...));
 168   }
 169
 170   // In C++, you can declare the function foo(void), but you can't pass a void
 171   // expression to foo. As a result, we must specialize the case of Callbacks
 172   // that have the void return type.
 173   void DispatchToCallback(base::Callback<void(ArgTypes...)> callback) {
 174     callback.Run(ArgumentHolder<indices, ArgTypes>::value...);
 175   }
 176
 177  private:
 178   static bool And() { return true; }
 179   template <typename... T>
 180   static bool And(bool arg1, T... args) {
 181     return arg1 && And(args...);
 182   }
 183
 184   Arguments* args_;
 185 };
 186
 187 // DispatchToCallback converts all the JavaScript arguments to C++ types and
 188 // invokes the base::Callback.
 189 template <typename Sig>
 190 struct Dispatcher {};
 191
 192 template <typename ReturnType, typename... ArgTypes>
 193 struct Dispatcher<ReturnType(ArgTypes...)> {
 194   static void DispatchToCallback(
 195       const v8::FunctionCallbackInfo<v8::Value>& info) {
 196     Arguments args(info);
 197     v8::Handle<v8::External> v8_holder;
 198     CHECK(args.GetData(&v8_holder));
 199     CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
 200         v8_holder->Value());
 201
 202     typedef CallbackHolder<ReturnType(ArgTypes...)> HolderT;
 203     HolderT* holder = static_cast<HolderT*>(holder_base);
 204
 205     using Indices = typename IndicesGenerator<sizeof...(ArgTypes)>::type;
 206     Invoker<Indices, ArgTypes...> invoker(&args, holder->flags);
 207     if (invoker.IsOK())
 208       invoker.DispatchToCallback(holder->callback);
 209   }
 210 };
 211
 212 }  // namespace internal
 213
 214
 215 // CreateFunctionTemplate creates a v8::FunctionTemplate that will create
 216 // JavaScript functions that execute a provided C++ function or base::Callback.
 217 // JavaScript arguments are automatically converted via gin::Converter, as is
 218 // the return value of the C++ function, if any.
 219 template<typename Sig>
 220 v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
 221     v8::Isolate* isolate, const base::Callback<Sig> callback,
 222     int callback_flags = 0) {
 223   typedef internal::CallbackHolder<Sig> HolderT;
 224   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 225
 226   return v8::FunctionTemplate::New(
 227       isolate,
 228       &internal::Dispatcher<Sig>::DispatchToCallback,
 229       ConvertToV8<v8::Handle<v8::External> >(isolate,
 230                                              holder->GetHandle(isolate)));
 231 }
 232
 233 // CreateFunctionHandler installs a CallAsFunction handler on the given
 234 // object template that forwards to a provided C++ function or base::Callback.
 235 template<typename Sig>
 236 void CreateFunctionHandler(v8::Isolate* isolate,
 237                            v8::Local<v8::ObjectTemplate> tmpl,
 238                            const base::Callback<Sig> callback,
 239                            int callback_flags = 0) {
 240   typedef internal::CallbackHolder<Sig> HolderT;
 241   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 242   tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
 243                                  ConvertToV8<v8::Handle<v8::External> >(
 244                                      isolate, holder->GetHandle(isolate)));
 245 }
 246
 247 }  // namespace gin
 248
 249 #endif  // GIN_FUNCTION_TEMPLATE_H_