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       // Ideally we would include the expected c++ type in the error
 136       // message which we can access via typeid(ArgType).name()
 137       // however we compile with no-rtti, which disables typeid.
 138       args->ThrowError();
 139     }
 140   }
 141 };
 142
 143 // Class template for converting arguments from JavaScript to C++ and running
 144 // the callback with them.
 145 template <typename IndicesType, typename... ArgTypes>
 146 class Invoker {};
 147
 148 template <size_t... indices, typename... ArgTypes>
 149 class Invoker<IndicesHolder<indices...>, ArgTypes...>
 150     : public ArgumentHolder<indices, ArgTypes>... {
 151  public:
 152   // Invoker<> inherits from ArgumentHolder<> for each argument.
 153   // C++ has always been strict about the class initialization order,
 154   // so it is guaranteed ArgumentHolders will be initialized (and thus, will
 155   // extract arguments from Arguments) in the right order.
 156   Invoker(Arguments* args, int create_flags)
 157       : ArgumentHolder<indices, ArgTypes>(args, create_flags)..., args_(args) {
 158     // GCC thinks that create_flags is going unused, even though the
 159     // expansion above clearly makes use of it. Per jyasskin@, casting
 160     // to void is the commonly accepted way to convince the compiler
 161     // that you're actually using a parameter/varible.
 162     (void)create_flags;
 163   }
 164
 165   bool IsOK() {
 166     return And(ArgumentHolder<indices, ArgTypes>::ok...);
 167   }
 168
 169   template <typename ReturnType>
 170   void DispatchToCallback(base::Callback<ReturnType(ArgTypes...)> callback) {
 171     args_->Return(callback.Run(ArgumentHolder<indices, ArgTypes>::value...));
 172   }
 173
 174   // In C++, you can declare the function foo(void), but you can't pass a void
 175   // expression to foo. As a result, we must specialize the case of Callbacks
 176   // that have the void return type.
 177   void DispatchToCallback(base::Callback<void(ArgTypes...)> callback) {
 178     callback.Run(ArgumentHolder<indices, ArgTypes>::value...);
 179   }
 180
 181  private:
 182   static bool And() { return true; }
 183   template <typename... T>
 184   static bool And(bool arg1, T... args) {
 185     return arg1 && And(args...);
 186   }
 187
 188   Arguments* args_;
 189 };
 190
 191 // DispatchToCallback converts all the JavaScript arguments to C++ types and
 192 // invokes the base::Callback.
 193 template <typename Sig>
 194 struct Dispatcher {};
 195
 196 template <typename ReturnType, typename... ArgTypes>
 197 struct Dispatcher<ReturnType(ArgTypes...)> {
 198   static void DispatchToCallback(
 199       const v8::FunctionCallbackInfo<v8::Value>& info) {
 200     Arguments args(info);
 201     v8::Handle<v8::External> v8_holder;
 202     CHECK(args.GetData(&v8_holder));
 203     CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
 204         v8_holder->Value());
 205
 206     typedef CallbackHolder<ReturnType(ArgTypes...)> HolderT;
 207     HolderT* holder = static_cast<HolderT*>(holder_base);
 208
 209     using Indices = typename IndicesGenerator<sizeof...(ArgTypes)>::type;
 210     Invoker<Indices, ArgTypes...> invoker(&args, holder->flags);
 211     if (invoker.IsOK())
 212       invoker.DispatchToCallback(holder->callback);
 213   }
 214 };
 215
 216 }  // namespace internal
 217
 218
 219 // CreateFunctionTemplate creates a v8::FunctionTemplate that will create
 220 // JavaScript functions that execute a provided C++ function or base::Callback.
 221 // JavaScript arguments are automatically converted via gin::Converter, as is
 222 // the return value of the C++ function, if any.
 223 //
 224 // NOTE: V8 caches FunctionTemplates for a lifetime of a web page for its own
 225 // internal reasons, thus it is generally a good idea to cache the template
 226 // returned by this function.  Otherwise, repeated method invocations from JS
 227 // will create substantial memory leaks. See http://crbug.com/463487.
 228 template<typename Sig>
 229 v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
 230     v8::Isolate* isolate, const base::Callback<Sig> callback,
 231     int callback_flags = 0) {
 232   typedef internal::CallbackHolder<Sig> HolderT;
 233   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 234
 235   return v8::FunctionTemplate::New(
 236       isolate,
 237       &internal::Dispatcher<Sig>::DispatchToCallback,
 238       ConvertToV8<v8::Handle<v8::External> >(isolate,
 239                                              holder->GetHandle(isolate)));
 240 }
 241
 242 // CreateFunctionHandler installs a CallAsFunction handler on the given
 243 // object template that forwards to a provided C++ function or base::Callback.
 244 template<typename Sig>
 245 void CreateFunctionHandler(v8::Isolate* isolate,
 246                            v8::Local<v8::ObjectTemplate> tmpl,
 247                            const base::Callback<Sig> callback,
 248                            int callback_flags = 0) {
 249   typedef internal::CallbackHolder<Sig> HolderT;
 250   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 251   tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
 252                                  ConvertToV8<v8::Handle<v8::External> >(
 253                                      isolate, holder->GetHandle(isolate)));
 254 }
 255
 256 }  // namespace gin
 257
 258 #endif  // GIN_FUNCTION_TEMPLATE_H_