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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#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(const_cast<T*>(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(const_cast<T*>(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:
using RefCountType = unsigned int;
using AllowOwnPtr = FalseType;
void ref() const
{
auto old_ref_count = m_ref_count.fetch_add(1, AK::MemoryOrder::memory_order_relaxed);
VERIFY(old_ref_count > 0);
VERIFY(!Checked<RefCountType>::addition_would_overflow(old_ref_count, 1));
}
[[nodiscard]] bool try_ref() const
{
RefCountType expected = m_ref_count.load(AK::MemoryOrder::memory_order_relaxed);
for (;;) {
if (expected == 0)
return false;
VERIFY(!Checked<RefCountType>::addition_would_overflow(expected, 1));
if (m_ref_count.compare_exchange_strong(expected, expected + 1, AK::MemoryOrder::memory_order_acquire))
return true;
}
}
[[nodiscard]] RefCountType ref_count() const
{
return m_ref_count.load(AK::MemoryOrder::memory_order_relaxed);
}
protected:
RefCountedBase() = default;
~RefCountedBase()
{
VERIFY(m_ref_count.load(AK::MemoryOrder::memory_order_relaxed) == 0);
}
RefCountType deref_base() const
{
auto old_ref_count = m_ref_count.fetch_sub(1, AK::MemoryOrder::memory_order_acq_rel);
VERIFY(old_ref_count > 0);
return old_ref_count - 1;
}
mutable Atomic<RefCountType> m_ref_count { 1 };
};
template<typename T>
class RefCounted : public RefCountedBase {
public:
bool 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);
return true;
} else if (new_ref_count == 1) {
call_one_ref_left_if_present(static_cast<const T*>(this));
}
return false;
}
};
}
using AK::RefCounted;
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