WebKit/Source/platform/bindings/ScriptWrappable.h

/*
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 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
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#ifndef ScriptWrappable_h
#define ScriptWrappable_h

#include "build/build_config.h"
#include "platform/PlatformExport.h"
#include "platform/bindings/ScriptWrappableVisitor.h"
#include "platform/bindings/WrapperTypeInfo.h"
#include "platform/heap/Handle.h"
#include "platform/wtf/Noncopyable.h"
#include "platform/wtf/TypeTraits.h"
#include "v8/include/v8.h"

namespace blink {

class PLATFORM_EXPORT TraceWrapperBase {
  WTF_MAKE_NONCOPYABLE(TraceWrapperBase);

 public:
  TraceWrapperBase() = default;
  virtual bool IsScriptWrappable() const { return false; }

  DECLARE_VIRTUAL_TRACE_WRAPPERS(){};
};

// ScriptWrappable provides a way to map from/to C++ DOM implementation to/from
// JavaScript object (platform object).  ToV8() converts a ScriptWrappable to
// a v8::Object and toScriptWrappable() converts a v8::Object back to
// a ScriptWrappable.  v8::Object as platform object is called "wrapper object".
// The wrapper object for the main world is stored in ScriptWrappable.  Wrapper
// objects for other worlds are stored in DOMWrapperMap.
class PLATFORM_EXPORT ScriptWrappable : public TraceWrapperBase {
  WTF_MAKE_NONCOPYABLE(ScriptWrappable);

 public:
  ScriptWrappable() {}

  bool IsScriptWrappable() const override { return true; }

  template <typename T>
  T* ToImpl() {
    // All ScriptWrappables are managed by the Blink GC heap; check that
    // |T| is a garbage collected type.
    static_assert(
        sizeof(T) && WTF::IsGarbageCollectedType<T>::value,
        "Classes implementing ScriptWrappable must be garbage collected.");

// Check if T* is castable to ScriptWrappable*, which means T doesn't
// have two or more ScriptWrappable as superclasses. If T has two
// ScriptWrappable as superclasses, conversions from T* to
// ScriptWrappable* are ambiguous.
#if !defined(COMPILER_MSVC)
    // MSVC 2013 doesn't support static_assert + constexpr well.
    static_assert(!static_cast<ScriptWrappable*>(static_cast<T*>(nullptr)),
                  "Class T must not have two or more ScriptWrappable as its "
                  "superclasses.");
#endif
    return static_cast<T*>(this);
  }

  // Returns the WrapperTypeInfo of the instance.
  //
  // This method must be overridden by DEFINE_WRAPPERTYPEINFO macro.
  virtual const WrapperTypeInfo* GetWrapperTypeInfo() const = 0;

  // Creates and returns a new wrapper object.
  virtual v8::Local<v8::Object> Wrap(v8::Isolate*,
                                     v8::Local<v8::Object> creation_context);

  // Associates the instance with the given |wrapper| if this instance is not
  // yet associated with any wrapper.  Returns the wrapper already associated
  // or |wrapper| if not yet associated.
  // The caller should always use the returned value rather than |wrapper|.
  WARN_UNUSED_RESULT virtual v8::Local<v8::Object> AssociateWithWrapper(
      v8::Isolate*,
      const WrapperTypeInfo*,
      v8::Local<v8::Object> wrapper);

  // Returns true if the instance needs to be kept alive even when the
  // instance is unreachable from JavaScript.
  virtual bool HasPendingActivity() const { return false; }

  // Associates this instance with the given |wrapper| if this instance is not
  // yet associated with any wrapper.  Returns true if the given wrapper is
  // associated with this instance, or false if this instance is already
  // associated with a wrapper.  In the latter case, |wrapper| will be updated
  // to the existing wrapper.
  WARN_UNUSED_RESULT bool SetWrapper(v8::Isolate* isolate,
                                     const WrapperTypeInfo* wrapper_type_info,
                                     v8::Local<v8::Object>& wrapper) {
    DCHECK(!wrapper.IsEmpty());
    if (UNLIKELY(ContainsWrapper())) {
      wrapper = MainWorldWrapper(isolate);
      return false;
    }
    main_world_wrapper_.Reset(isolate, wrapper);
    wrapper_type_info->ConfigureWrapper(&main_world_wrapper_);
    main_world_wrapper_.SetWeak();
    DCHECK(ContainsWrapper());
    ScriptWrappableVisitor::WriteBarrier(isolate, &main_world_wrapper_);
    return true;
  }

  // Dissociates the wrapper, if any, from this instance.
  void UnsetWrapperIfAny() {
    if (ContainsWrapper()) {
      main_world_wrapper_.Reset();
      WrapperTypeInfo::WrapperDestroyed();
    }
  }

  bool IsEqualTo(const v8::Local<v8::Object>& other) const {
    return main_world_wrapper_ == other;
  }

  bool SetReturnValue(v8::ReturnValue<v8::Value> return_value) {
    return_value.Set(main_world_wrapper_);
    return ContainsWrapper();
  }

  bool ContainsWrapper() const { return !main_world_wrapper_.IsEmpty(); }

  //  Mark wrapper of this ScriptWrappable as alive in V8. Only marks
  //  wrapper in the main world. To mark wrappers in all worlds call
  //  ScriptWrappableVisitor::markWrapper(ScriptWrappable*, v8::Isolate*)
  void MarkWrapper(const ScriptWrappableVisitor*) const;

 private:
  // These classes are exceptionally allowed to use mainWorldWrapper().
  friend class DOMDataStore;
  friend class HeapSnaphotWrapperVisitor;
  friend class V8HiddenValue;
  friend class V8PrivateProperty;

  v8::Local<v8::Object> MainWorldWrapper(v8::Isolate* isolate) const {
    return v8::Local<v8::Object>::New(isolate, main_world_wrapper_);
  }

  // Only use when really necessary, i.e., when passing over this
  // ScriptWrappable's reference to V8. Should only be needed by GC
  // infrastructure.
  const v8::Persistent<v8::Object>* RawMainWorldWrapper() const {
    return &main_world_wrapper_;
  }

  v8::Persistent<v8::Object> main_world_wrapper_;
};

// Defines 'wrapperTypeInfo' virtual method which returns the WrapperTypeInfo of
// the instance. Also declares a static member of type WrapperTypeInfo, of which
// the definition is given by the IDL code generator.
//
// All the derived classes of ScriptWrappable, regardless of directly or
// indirectly, must write this macro in the class definition as long as the
// class has a corresponding .idl file.
#define DEFINE_WRAPPERTYPEINFO()                               \
 public:                                                       \
  const WrapperTypeInfo* GetWrapperTypeInfo() const override { \
    return &wrapper_type_info_;                                \
  }                                                            \
                                                               \
 private:                                                      \
  static const WrapperTypeInfo& wrapper_type_info_

// Declares 'wrapperTypeInfo' method without definition.
//
// This macro is used for template classes. e.g. DOMTypedArray<>.
// To export such a template class X, we need to instantiate X with EXPORT_API,
// i.e. "extern template class EXPORT_API X;"
// However, once we instantiate X, we cannot specialize X after
// the instantiation. i.e. we will see "error: explicit specialization of ...
// after instantiation". So we cannot define X's s_wrapperTypeInfo in generated
// code by using specialization. Instead, we need to implement wrapperTypeInfo
// in X's cpp code, and instantiate X, i.e. "template class X;".
#define DECLARE_WRAPPERTYPEINFO()                             \
 public:                                                      \
  const WrapperTypeInfo* GetWrapperTypeInfo() const override; \
                                                              \
 private:                                                     \
  typedef void end_of_define_wrappertypeinfo_not_reached_t

}  // namespace blink

#endif  // ScriptWrappable_h