ladybird/AK/RefCounted.h
Sergey Bugaev 3ff651323c AK: Ensure RefCounted types are never copied or moved
Before this, it has been possible to assign a RefCounted object to another
RefCounted object. Hilariosly (or sadly), that copied the refcount among
the other fields, meaning the target value ended up with a wrong refcount.

Ensure this never happens by disallowing copies and moves for RefCounted types.
2020-06-12 16:08:45 +02:00

125 lines
3.5 KiB
C++

/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. 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.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <AK/Assertions.h>
#include <AK/Atomic.h>
#include <AK/Checked.h>
#include <AK/Noncopyable.h>
#include <AK/Platform.h>
#include <AK/StdLibExtras.h>
namespace AK {
template<class T>
constexpr auto call_will_be_destroyed_if_present(const T* object) -> decltype(object->will_be_destroyed(), TrueType {})
{
const_cast<T*>(object)->will_be_destroyed();
return {};
}
constexpr auto call_will_be_destroyed_if_present(...) -> FalseType
{
return {};
}
template<class T>
constexpr auto call_one_ref_left_if_present(const T* object) -> decltype(object->one_ref_left(), TrueType {})
{
const_cast<T*>(object)->one_ref_left();
return {};
}
constexpr auto call_one_ref_left_if_present(...) -> FalseType
{
return {};
}
class RefCountedBase {
AK_MAKE_NONCOPYABLE(RefCountedBase)
AK_MAKE_NONMOVABLE(RefCountedBase)
public:
typedef unsigned int RefCountType;
ALWAYS_INLINE void ref() const
{
auto old_ref_count = m_ref_count++;
ASSERT(old_ref_count > 0);
ASSERT(!Checked<RefCountType>::addition_would_overflow(old_ref_count, 1));
}
ALWAYS_INLINE RefCountType ref_count() const
{
return m_ref_count;
}
protected:
RefCountedBase() { }
ALWAYS_INLINE ~RefCountedBase()
{
ASSERT(m_ref_count == 0);
}
ALWAYS_INLINE RefCountType deref_base() const
{
auto old_ref_count = m_ref_count--;
ASSERT(old_ref_count > 0);
return old_ref_count - 1;
}
mutable Atomic<RefCountType> m_ref_count { 1 };
};
template<typename T>
class RefCounted : public RefCountedBase {
public:
void unref() const
{
auto new_ref_count = deref_base();
if (new_ref_count == 0) {
call_will_be_destroyed_if_present(static_cast<const T*>(this));
delete static_cast<const T*>(this);
} else if (new_ref_count == 1) {
call_one_ref_left_if_present(static_cast<const T*>(this));
}
}
};
static constexpr bool is_ref_counted(const RefCountedBase*)
{
return true;
}
static constexpr bool is_ref_counted(...)
{
return false;
}
}
using AK::RefCounted;