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