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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Weakable.h>
namespace AK {
template<typename T>
class WeakPtr {
template<typename U>
friend class Weakable;
public:
WeakPtr() = default;
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(const WeakPtr<U>& other)
: m_link(other.m_link)
{
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(WeakPtr<U>&& other)
: m_link(other.take_link())
{
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(WeakPtr<U>&& other)
{
m_link = other.take_link();
return *this;
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(const WeakPtr<U>& other)
{
if ((const void*)this != (const void*)&other)
m_link = other.m_link;
return *this;
}
WeakPtr& operator=(std::nullptr_t)
{
clear();
return *this;
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(const U& object)
: m_link(object.template make_weak_ptr<U>().take_link())
{
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(const U* object)
{
if (object)
m_link = object->template make_weak_ptr<U>().take_link();
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(const RefPtr<U>& object)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template make_weak_ptr<U>().take_link();
});
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr(const NonnullRefPtr<U>& object)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template make_weak_ptr<U>().take_link();
});
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(const U& object)
{
m_link = object.template make_weak_ptr<U>().take_link();
return *this;
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(const U* object)
{
if (object)
m_link = object->template make_weak_ptr<U>().take_link();
else
m_link = nullptr;
return *this;
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(const RefPtr<U>& object)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template make_weak_ptr<U>().take_link();
else
m_link = nullptr;
});
return *this;
}
template<typename U, typename EnableIf<IsBaseOf<T, U>>::Type* = nullptr>
WeakPtr& operator=(const NonnullRefPtr<U>& object)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template make_weak_ptr<U>().take_link();
else
m_link = nullptr;
});
return *this;
}
[[nodiscard]] RefPtr<T> strong_ref() const
{
// This only works with RefCounted objects, but it is the only
// safe way to get a strong reference from a WeakPtr. Any code
// that uses objects not derived from RefCounted will have to
// use unsafe_ptr(), but as the name suggests, it is not safe...
RefPtr<T> ref;
// Using do_while_locked protects against a race with clear()!
m_link.do_while_locked([&](WeakLink* link) {
if (link)
ref = link->template strong_ref<T>();
});
return ref;
}
#ifndef KERNEL
// A lot of user mode code is single-threaded. But for kernel mode code
// this is generally not true as everything is multi-threaded. So make
// these shortcuts and aliases only available to non-kernel code.
T* ptr() const { return unsafe_ptr(); }
T* operator->() { return unsafe_ptr(); }
const T* operator->() const { return unsafe_ptr(); }
operator const T*() const { return unsafe_ptr(); }
operator T*() { return unsafe_ptr(); }
#endif
[[nodiscard]] T* unsafe_ptr() const
{
T* ptr = nullptr;
m_link.do_while_locked([&](WeakLink* link) {
if (link)
ptr = link->unsafe_ptr<T>();
});
return ptr;
}
operator bool() const { return m_link ? !m_link->is_null() : false; }
[[nodiscard]] bool is_null() const { return !m_link || m_link->is_null(); }
void clear() { m_link = nullptr; }
[[nodiscard]] RefPtr<WeakLink> take_link() { return move(m_link); }
private:
WeakPtr(const RefPtr<WeakLink>& link)
: m_link(link)
{
}
RefPtr<WeakLink> m_link;
};
template<typename T>
template<typename U>
inline WeakPtr<U> Weakable<T>::make_weak_ptr() const
{
if constexpr (IsBaseOf<RefCountedBase, T>) {
// Checking m_being_destroyed isn't sufficient when dealing with
// a RefCounted type.The reference count will drop to 0 before the
// destructor is invoked and revoke_weak_ptrs is called. So, try
// to add a ref (which should fail if the ref count is at 0) so
// that we prevent the destructor and revoke_weak_ptrs from being
// triggered until we're done.
if (!static_cast<const T*>(this)->try_ref())
return {};
} else {
// For non-RefCounted types this means a weak reference can be
// obtained until the ~Weakable destructor is invoked!
if (m_being_destroyed.load(AK::MemoryOrder::memory_order_acquire))
return {};
}
if (!m_link) {
// There is a small chance that we create a new WeakLink and throw
// it away because another thread beat us to it. But the window is
// pretty small and the overhead isn't terrible.
m_link.assign_if_null(adopt_ref(*new WeakLink(const_cast<T&>(static_cast<const T&>(*this)))));
}
WeakPtr<U> weak_ptr(m_link);
if constexpr (IsBaseOf<RefCountedBase, T>) {
// Now drop the reference we temporarily added
if (static_cast<const T*>(this)->unref()) {
// We just dropped the last reference, which should have called
// revoke_weak_ptrs, which should have invalidated our weak_ptr
VERIFY(!weak_ptr.strong_ref());
return {};
}
}
return weak_ptr;
}
template<typename T>
struct Formatter<WeakPtr<T>> : Formatter<const T*> {
ErrorOr<void> format(FormatBuilder& builder, WeakPtr<T> const& value)
{
#ifdef KERNEL
auto ref = value.strong_ref();
return Formatter<const T*>::format(builder, ref.ptr());
#else
return Formatter<const T*>::format(builder, value.ptr());
#endif
}
};
template<typename T>
WeakPtr<T> try_make_weak_ptr(const T* ptr)
{
if (ptr) {
return ptr->template make_weak_ptr<T>();
}
return {};
}
}
using AK::WeakPtr;
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