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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_MEMORY_SCOPED_REFPTR_H_
#define BASE_MEMORY_SCOPED_REFPTR_H_
#include <stddef.h>
#include <iosfwd>
#include <type_traits>
#include <utility>
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"
template <class T>
class scoped_refptr;
namespace base {
template <class, typename>
class RefCounted;
template <class, typename>
class RefCountedThreadSafe;
class SequencedTaskRunner;
class WrappedPromise;
template <typename T>
scoped_refptr<T> AdoptRef(T* t);
namespace internal {
class BasePromise;
} // namespace internal
namespace subtle {
enum AdoptRefTag { kAdoptRefTag };
enum StartRefCountFromZeroTag { kStartRefCountFromZeroTag };
enum StartRefCountFromOneTag { kStartRefCountFromOneTag };
template <typename T, typename U, typename V>
constexpr bool IsRefCountPreferenceOverridden(const T*,
const RefCounted<U, V>*) {
return !std::is_same<std::decay_t<decltype(T::kRefCountPreference)>,
std::decay_t<decltype(U::kRefCountPreference)>>::value;
}
template <typename T, typename U, typename V>
constexpr bool IsRefCountPreferenceOverridden(
const T*,
const RefCountedThreadSafe<U, V>*) {
return !std::is_same<std::decay_t<decltype(T::kRefCountPreference)>,
std::decay_t<decltype(U::kRefCountPreference)>>::value;
}
constexpr bool IsRefCountPreferenceOverridden(...) {
return false;
}
} // namespace subtle
// Creates a scoped_refptr from a raw pointer without incrementing the reference
// count. Use this only for a newly created object whose reference count starts
// from 1 instead of 0.
template <typename T>
scoped_refptr<T> AdoptRef(T* obj) {
using Tag = std::decay_t<decltype(T::kRefCountPreference)>;
static_assert(std::is_same<subtle::StartRefCountFromOneTag, Tag>::value,
"Use AdoptRef only if the reference count starts from one.");
DCHECK(obj);
DCHECK(obj->HasOneRef());
obj->Adopted();
return scoped_refptr<T>(obj, subtle::kAdoptRefTag);
}
namespace subtle {
template <typename T>
scoped_refptr<T> AdoptRefIfNeeded(T* obj, StartRefCountFromZeroTag) {
return scoped_refptr<T>(obj);
}
template <typename T>
scoped_refptr<T> AdoptRefIfNeeded(T* obj, StartRefCountFromOneTag) {
return AdoptRef(obj);
}
} // namespace subtle
// Constructs an instance of T, which is a ref counted type, and wraps the
// object into a scoped_refptr<T>.
template <typename T, typename... Args>
scoped_refptr<T> MakeRefCounted(Args&&... args) {
T* obj = new T(std::forward<Args>(args)...);
return subtle::AdoptRefIfNeeded(obj, T::kRefCountPreference);
}
// Takes an instance of T, which is a ref counted type, and wraps the object
// into a scoped_refptr<T>.
template <typename T>
scoped_refptr<T> WrapRefCounted(T* t) {
return scoped_refptr<T>(t);
}
} // namespace base
//
// A smart pointer class for reference counted objects. Use this class instead
// of calling AddRef and Release manually on a reference counted object to
// avoid common memory leaks caused by forgetting to Release an object
// reference. Sample usage:
//
// class MyFoo : public RefCounted<MyFoo> {
// ...
// private:
// friend class RefCounted<MyFoo>; // Allow destruction by RefCounted<>.
// ~MyFoo(); // Destructor must be private/protected.
// };
//
// void some_function() {
// scoped_refptr<MyFoo> foo = MakeRefCounted<MyFoo>();
// foo->Method(param);
// // |foo| is released when this function returns
// }
//
// void some_other_function() {
// scoped_refptr<MyFoo> foo = MakeRefCounted<MyFoo>();
// ...
// foo.reset(); // explicitly releases |foo|
// ...
// if (foo)
// foo->Method(param);
// }
//
// The above examples show how scoped_refptr<T> acts like a pointer to T.
// Given two scoped_refptr<T> classes, it is also possible to exchange
// references between the two objects, like so:
//
// {
// scoped_refptr<MyFoo> a = MakeRefCounted<MyFoo>();
// scoped_refptr<MyFoo> b;
//
// b.swap(a);
// // now, |b| references the MyFoo object, and |a| references nullptr.
// }
//
// To make both |a| and |b| in the above example reference the same MyFoo
// object, simply use the assignment operator:
//
// {
// scoped_refptr<MyFoo> a = MakeRefCounted<MyFoo>();
// scoped_refptr<MyFoo> b;
//
// b = a;
// // now, |a| and |b| each own a reference to the same MyFoo object.
// }
//
// Also see Chromium's ownership and calling conventions:
// Specifically:
// If the function (at least sometimes) takes a ref on a refcounted object,
// declare the param as scoped_refptr<T>. The caller can decide whether it
// wishes to transfer ownership (by calling std::move(t) when passing t) or
// retain its ref (by simply passing t directly).
// In other words, use scoped_refptr like you would a std::unique_ptr except
// in the odd case where it's required to hold on to a ref while handing one
// to another component (if a component merely needs to use t on the stack
// without keeping a ref: pass t as a raw T*).
template <class T>
class scoped_refptr {
public:
typedef T element_type;
constexpr scoped_refptr() = default;
// Allow implicit construction from nullptr.
constexpr scoped_refptr(std::nullptr_t) {}
// Constructs from a raw pointer. Note that this constructor allows implicit
// conversion from T* to scoped_refptr<T> which is strongly discouraged. If
// you are creating a new ref-counted object please use
// base::MakeRefCounted<T>() or base::WrapRefCounted<T>(). Otherwise you
// should move or copy construct from an existing scoped_refptr<T> to the
// ref-counted object.
scoped_refptr(T* p) : ptr_(p) {
if (ptr_)
AddRef(ptr_);
}
// Copy constructor. This is required in addition to the copy conversion
// constructor below.
scoped_refptr(const scoped_refptr& r) : scoped_refptr(r.ptr_) {}
// Copy conversion constructor.
template <typename U,
typename = typename std::enable_if<
std::is_convertible<U*, T*>::value>::type>
scoped_refptr(const scoped_refptr<U>& r) : scoped_refptr(r.ptr_) {}
// Move constructor. This is required in addition to the move conversion
// constructor below.
scoped_refptr(scoped_refptr&& r) noexcept : ptr_(r.ptr_) { r.ptr_ = nullptr; }
// Move conversion constructor.
template <typename U,
typename = typename std::enable_if<
std::is_convertible<U*, T*>::value>::type>
scoped_refptr(scoped_refptr<U>&& r) noexcept : ptr_(r.ptr_) {
r.ptr_ = nullptr;
}
~scoped_refptr() {
static_assert(!base::subtle::IsRefCountPreferenceOverridden(
static_cast<T*>(nullptr), static_cast<T*>(nullptr)),
"It's unsafe to override the ref count preference."
" Please remove REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE"
" from subclasses.");
if (ptr_)
Release(ptr_);
}
T* get() const { return ptr_; }
T& operator*() const {
DCHECK(ptr_);
return *ptr_;
}
T* operator->() const {
DCHECK(ptr_);
return ptr_;
}
scoped_refptr& operator=(std::nullptr_t) {
reset();
return *this;
}
scoped_refptr& operator=(T* p) { return *this = scoped_refptr(p); }
// Unified assignment operator.
scoped_refptr& operator=(scoped_refptr r) noexcept {
swap(r);
return *this;
}
// Sets managed object to null and releases reference to the previous managed
// object, if it existed.
void reset() { scoped_refptr().swap(*this); }
void swap(scoped_refptr& r) noexcept { std::swap(ptr_, r.ptr_); }
explicit operator bool() const { return ptr_ != nullptr; }
template <typename U>
bool operator==(const scoped_refptr<U>& rhs) const {
return ptr_ == rhs.get();
}
template <typename U>
bool operator!=(const scoped_refptr<U>& rhs) const {
return !operator==(rhs);
}
template <typename U>
bool operator<(const scoped_refptr<U>& rhs) const {
return ptr_ < rhs.get();
}
protected:
T* ptr_ = nullptr;
private:
template <typename U>
friend scoped_refptr<U> base::AdoptRef(U*);
friend class ::base::SequencedTaskRunner;
// Friend access so these classes can use the constructor below as part of a
// binary size optimization.
friend class ::base::internal::BasePromise;
friend class ::base::WrappedPromise;
// Returns the owned pointer (if any), releasing ownership to the caller. The
// caller is responsible for managing the lifetime of the reference.
T* release();
scoped_refptr(T* p, base::subtle::AdoptRefTag) : ptr_(p) {}
// Friend required for move constructors that set r.ptr_ to null.
template <typename U>
friend class scoped_refptr;
// Non-inline helpers to allow:
// class Opaque;
// extern template class scoped_refptr<Opaque>;
// Otherwise the compiler will complain that Opaque is an incomplete type.
static void AddRef(T* ptr);
static void Release(T* ptr);
};
template <typename T>
T* scoped_refptr<T>::release() {
T* ptr = ptr_;
ptr_ = nullptr;
return ptr;
}
// static
template <typename T>
void scoped_refptr<T>::AddRef(T* ptr) {
ptr->AddRef();
}
// static
template <typename T>
void scoped_refptr<T>::Release(T* ptr) {
ptr->Release();
}
template <typename T, typename U>
bool operator==(const scoped_refptr<T>& lhs, const U* rhs) {
return lhs.get() == rhs;
}
template <typename T, typename U>
bool operator==(const T* lhs, const scoped_refptr<U>& rhs) {
return lhs == rhs.get();
}
template <typename T>
bool operator==(const scoped_refptr<T>& lhs, std::nullptr_t null) {
return !static_cast<bool>(lhs);
}
template <typename T>
bool operator==(std::nullptr_t null, const scoped_refptr<T>& rhs) {
return !static_cast<bool>(rhs);
}
template <typename T, typename U>
bool operator!=(const scoped_refptr<T>& lhs, const U* rhs) {
return !operator==(lhs, rhs);
}
template <typename T, typename U>
bool operator!=(const T* lhs, const scoped_refptr<U>& rhs) {
return !operator==(lhs, rhs);
}
template <typename T>
bool operator!=(const scoped_refptr<T>& lhs, std::nullptr_t null) {
return !operator==(lhs, null);
}
template <typename T>
bool operator!=(std::nullptr_t null, const scoped_refptr<T>& rhs) {
return !operator==(null, rhs);
}
template <typename T>
std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p) {
return out << p.get();
}
template <typename T>
void swap(scoped_refptr<T>& lhs, scoped_refptr<T>& rhs) noexcept {
lhs.swap(rhs);
}
#endif // BASE_MEMORY_SCOPED_REFPTR_H_