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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <Kernel/Library/LockWeakable.h>
namespace AK {
template<typename T>
class [[nodiscard]] LockWeakPtr {
template<typename U>
friend class LockWeakable;
public:
LockWeakPtr() = default;
template<typename U>
LockWeakPtr(WeakPtr<U> const& other)
requires(IsBaseOf<T, U>)
: m_link(other.m_link)
{
}
template<typename U>
LockWeakPtr(WeakPtr<U>&& other)
requires(IsBaseOf<T, U>)
: m_link(other.take_link())
{
}
template<typename U>
LockWeakPtr& operator=(WeakPtr<U>&& other)
requires(IsBaseOf<T, U>)
{
m_link = other.take_link();
return *this;
}
template<typename U>
LockWeakPtr& operator=(WeakPtr<U> const& other)
requires(IsBaseOf<T, U>)
{
if ((void const*)this != (void const*)&other)
m_link = other.m_link;
return *this;
}
LockWeakPtr& operator=(nullptr_t)
{
clear();
return *this;
}
template<typename U>
LockWeakPtr(U const& object)
requires(IsBaseOf<T, U>)
: m_link(object.template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link())
{
}
template<typename U>
LockWeakPtr(U const* object)
requires(IsBaseOf<T, U>)
{
if (object)
m_link = object->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
}
template<typename U>
LockWeakPtr(LockRefPtr<U> const& object)
requires(IsBaseOf<T, U>)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
});
}
template<typename U>
LockWeakPtr(NonnullLockRefPtr<U> const& object)
requires(IsBaseOf<T, U>)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
});
}
template<typename U>
LockWeakPtr& operator=(U const& object)
requires(IsBaseOf<T, U>)
{
m_link = object.template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
return *this;
}
template<typename U>
LockWeakPtr& operator=(U const* object)
requires(IsBaseOf<T, U>)
{
if (object)
m_link = object->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
else
m_link = nullptr;
return *this;
}
template<typename U>
LockWeakPtr& operator=(LockRefPtr<U> const& object)
requires(IsBaseOf<T, U>)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
else
m_link = nullptr;
});
return *this;
}
template<typename U>
LockWeakPtr& operator=(NonnullLockRefPtr<U> const& object)
requires(IsBaseOf<T, U>)
{
object.do_while_locked([&](U* obj) {
if (obj)
m_link = obj->template try_make_weak_ptr<U>().release_value_but_fixme_should_propagate_errors().take_link();
else
m_link = nullptr;
});
return *this;
}
[[nodiscard]] LockRefPtr<T> strong_ref() const
{
// This only works with RefCounted objects, but it is the only
// safe way to get a strong reference from a LockWeakPtr. Any code
// that uses objects not derived from RefCounted will have to
// use unsafe_ptr(), but as the name suggests, it is not safe...
LockRefPtr<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;
}
[[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]] LockRefPtr<WeakLink> take_link() { return move(m_link); }
private:
LockWeakPtr(LockRefPtr<WeakLink> const& link)
: m_link(link)
{
}
LockRefPtr<WeakLink> m_link;
};
template<typename T>
template<typename U>
inline ErrorOr<LockWeakPtr<U>> LockWeakable<T>::try_make_weak_ptr() const
{
if constexpr (IsBaseOf<AtomicRefCountedBase, 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<T const*>(this)->try_ref())
return LockWeakPtr<U> {};
} else {
// For non-RefCounted types this means a weak reference can be
// obtained until the ~LockWeakable destructor is invoked!
if (m_being_destroyed.load(AK::MemoryOrder::memory_order_acquire))
return LockWeakPtr<U> {};
}
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(TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) WeakLink(const_cast<T&>(static_cast<T const&>(*this))))));
}
LockWeakPtr<U> weak_ptr(m_link);
if constexpr (IsBaseOf<AtomicRefCountedBase, T>) {
// Now drop the reference we temporarily added
if (static_cast<T const*>(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 LockWeakPtr<U> {};
}
}
return weak_ptr;
}
template<typename T>
struct Formatter<LockWeakPtr<T>> : Formatter<T const*> {
ErrorOr<void> format(FormatBuilder& builder, LockWeakPtr<T> const& value)
{
auto ref = value.strong_ref();
return Formatter<T const*>::format(builder, ref.ptr());
}
};
template<typename T>
ErrorOr<LockWeakPtr<T>> try_make_weak_ptr_if_nonnull(T const* ptr)
{
if (ptr) {
return ptr->template try_make_weak_ptr<T>();
}
return LockWeakPtr<T> {};
}
}
using AK::LockWeakPtr;
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