cef/include/base/cef_scoped_refptr.h

// Copyright (c) 2017 Marshall A. Greenblatt. Portions copyright (c) 2011
// Google Inc. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the name Chromium Embedded
// Framework nor the names of its contributors may be used to endorse
// or promote products derived from this software without specific prior
// written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef CEF_INCLUDE_BASE_CEF_SCOPED_REFPTR_H_
#define CEF_INCLUDE_BASE_CEF_SCOPED_REFPTR_H_
#pragma once

#if defined(USING_CHROMIUM_INCLUDES)
// When building CEF include the Chromium header directly.
#include "base/memory/scoped_refptr.h"
#else  // !USING_CHROMIUM_INCLUDES
// The following is substantially similar to the Chromium implementation.
// If the Chromium implementation diverges the below implementation should be
// updated to match.

#include <stddef.h>

#include <iosfwd>
#include <type_traits>
#include <utility>

#include "include/base/cef_logging.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 cef_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 cef_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<cef_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, cef_subtle::kAdoptRefTag);
}

namespace cef_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 cef_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 cef_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:
///
/// <pre>
///   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);
///   }
/// </pre>
///
/// 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:
///
/// <pre>
///   {
///     scoped_refptr<MyFoo> a = MakeRefCounted<MyFoo>();
///     scoped_refptr<MyFoo> b;
///
///     b.swap(a);
///     // now, |b| references the MyFoo object, and |a| references nullptr.
///   }
/// </pre>
///
/// To make both |a| and |b| in the above example reference the same MyFoo
/// object, simply use the assignment operator:
///
/// <pre>
///   {
///     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.
///   }
/// </pre>
///
/// Also see Chromium's ownership and calling conventions:
/// https://chromium.googlesource.com/chromium/src/+/lkgr/styleguide/c++/c++.md#object-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 TRIVIAL_ABI 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::cef_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); }

  // Returns the owned pointer (if any), releasing ownership to the caller. The
  // caller is responsible for managing the lifetime of the reference.
  [[nodiscard]] T* release();

  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;

  scoped_refptr(T* p, base::cef_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  // !USING_CHROMIUM_INCLUDES

#endif  // CEF_INCLUDE_BASE_CEF_SCOPED_REFPTR_H_