blob: 2a55d863c1eec031a8a428884c68d92161f40369 [file] [log] [blame]
* Copyright 2016 The WebRTC Project Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <type_traits>
#include <utility>
#include "api/scoped_refptr.h"
#include "rtc_base/constructor_magic.h"
#include "rtc_base/ref_count.h"
#include "rtc_base/ref_counter.h"
namespace rtc {
template <class T>
class RefCountedObject : public T {
RefCountedObject() {}
template <class P0>
explicit RefCountedObject(P0&& p0) : T(std::forward<P0>(p0)) {}
template <class P0, class P1, class... Args>
RefCountedObject(P0&& p0, P1&& p1, Args&&... args)
: T(std::forward<P0>(p0),
std::forward<Args>(args)...) {}
void AddRef() const override { ref_count_.IncRef(); }
RefCountReleaseStatus Release() const override {
const auto status = ref_count_.DecRef();
if (status == RefCountReleaseStatus::kDroppedLastRef) {
delete this;
return status;
// Return whether the reference count is one. If the reference count is used
// in the conventional way, a reference count of 1 implies that the current
// thread owns the reference and no other thread shares it. This call
// performs the test for a reference count of one, and performs the memory
// barrier needed for the owning thread to act on the object, knowing that it
// has exclusive access to the object.
virtual bool HasOneRef() const { return ref_count_.HasOneRef(); }
~RefCountedObject() override {}
mutable webrtc::webrtc_impl::RefCounter ref_count_{0};
template <class T>
class FinalRefCountedObject final : public T {
using T::T;
// Until c++17 compilers are allowed not to inherit the default constructors.
// Thus the default constructors are forwarded explicitly.
FinalRefCountedObject() = default;
explicit FinalRefCountedObject(const T& other) : T(other) {}
explicit FinalRefCountedObject(T&& other) : T(std::move(other)) {}
FinalRefCountedObject(const FinalRefCountedObject&) = delete;
FinalRefCountedObject& operator=(const FinalRefCountedObject&) = delete;
void AddRef() const { ref_count_.IncRef(); }
RefCountReleaseStatus Release() const {
const auto status = ref_count_.DecRef();
if (status == RefCountReleaseStatus::kDroppedLastRef) {
delete this;
return status;
bool HasOneRef() const { return ref_count_.HasOneRef(); }
~FinalRefCountedObject() = default;
mutable webrtc::webrtc_impl::RefCounter ref_count_{0};
// General utilities for constructing a reference counted class and the
// appropriate reference count implementation for that class.
// These utilities select either the `RefCountedObject` implementation or
// `FinalRefCountedObject` depending on whether the to-be-shared class is
// derived from the RefCountInterface interface or not (respectively).
// `make_ref_counted`:
// Use this when you want to construct a reference counted object of type T and
// get a `scoped_refptr<>` back. Example:
// auto p = make_ref_counted<Foo>("bar", 123);
// For a class that inherits from RefCountInterface, this is equivalent to:
// auto p = scoped_refptr<Foo>(new RefCountedObject<Foo>("bar", 123));
// If the class does not inherit from RefCountInterface, the example is
// equivalent to:
// auto p = scoped_refptr<FinalRefCountedObject<Foo>>(
// new FinalRefCountedObject<Foo>("bar", 123));
// In these cases, `make_ref_counted` reduces the amount of boilerplate code but
// also helps with the most commonly intended usage of RefCountedObject whereby
// methods for reference counting, are virtual and designed to satisfy the need
// of an interface. When such a need does not exist, it is more efficient to use
// the `FinalRefCountedObject` template, which does not add the vtable overhead.
// Note that in some cases, using RefCountedObject directly may still be what's
// needed.
// `make_ref_counted` for classes that are convertible to RefCountInterface.
template <
typename T,
typename... Args,
typename std::enable_if<std::is_convertible<T*, RefCountInterface*>::value,
T>::type* = nullptr>
scoped_refptr<T> make_ref_counted(Args&&... args) {
return new RefCountedObject<T>(std::forward<Args>(args)...);
// `make_ref_counted` for complete classes that are not convertible to
// RefCountInterface.
template <
typename T,
typename... Args,
typename std::enable_if<!std::is_convertible<T*, RefCountInterface*>::value,
T>::type* = nullptr>
scoped_refptr<FinalRefCountedObject<T>> make_ref_counted(Args&&... args) {
return new FinalRefCountedObject<T>(std::forward<Args>(args)...);
// `Ref<>`, `Ref<>::Type` and `Ref<>::Ptr`:
// `Ref` is a type declaring utility that is compatible with `make_ref_counted`
// and can be used in classes and methods where it's more convenient (or
// readable) to have the compiler figure out the fully fleshed out type for a
// class rather than spell it out verbatim in all places the type occurs (which
// can mean maintenance work if the class layout changes).
// Usage examples:
// If you want to declare the parameter type that's always compatible with
// this code:
// Bar(make_ref_counted<Foo>());
// You can use `Ref<>::Ptr` to declare a compatible scoped_refptr type:
// void Bar(Ref<Foo>::Ptr p);
// This might be more practically useful in templates though.
// In rare cases you might need to be able to declare a parameter that's fully
// compatible with the reference counted T type - and just using T* is not
// enough. To give a code example, we can declare a function, `Foo` that is
// compatible with this code:
// auto p = make_ref_counted<Foo>();
// Foo(p.get());
// void Foo(Ref<Foo>::Type* foo_ptr);
// Alternatively this would be:
// void Foo(Foo* foo_ptr);
// or
// void Foo(FinalRefCountedObject<Foo>* foo_ptr);
// Declares the approprate reference counted type for T depending on whether
// T is convertible to RefCountInterface or not.
// For classes that are convertible, the type will simply be T.
// For classes that cannot be converted to RefCountInterface, the type will be
// FinalRefCountedObject<T>.
// This is most useful for declaring a scoped_refptr<T> instance for a class
// that may or may not implement a virtual reference counted interface:
// * scoped_refptr<Ref<Foo>::Type> my_ptr;
template <typename T>
struct Ref {
typedef typename std::conditional<
std::is_convertible<T*, RefCountInterface*>::value,
FinalRefCountedObject<T>>::type Type;
typedef scoped_refptr<Type> Ptr;
} // namespace rtc