ladybird/AK/NonnullRefPtr.h

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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/Format.h>
#include <AK/Traits.h>
#include <AK/Types.h>
#ifdef KERNEL
# include <Kernel/Arch/x86/CPU.h>
#endif
namespace AK {
template<typename T>
class OwnPtr;
template<typename T, typename PtrTraits>
class RefPtr;
template<typename T>
ALWAYS_INLINE void ref_if_not_null(T* ptr)
{
if (ptr)
ptr->ref();
}
template<typename T>
ALWAYS_INLINE void unref_if_not_null(T* ptr)
{
if (ptr)
ptr->unref();
}
template<typename T>
class NonnullRefPtr {
template<typename U, typename P>
friend class RefPtr;
template<typename U>
friend class NonnullRefPtr;
template<typename U>
friend class WeakPtr;
public:
using ElementType = T;
enum AdoptTag { Adopt };
ALWAYS_INLINE NonnullRefPtr(const T& object)
: m_bits((FlatPtr)&object)
{
VERIFY(!(m_bits & 1));
const_cast<T&>(object).ref();
}
template<typename U>
ALWAYS_INLINE NonnullRefPtr(const U& object)
: m_bits((FlatPtr) static_cast<const T*>(&object))
{
VERIFY(!(m_bits & 1));
const_cast<T&>(static_cast<const T&>(object)).ref();
}
ALWAYS_INLINE NonnullRefPtr(AdoptTag, T& object)
: m_bits((FlatPtr)&object)
{
VERIFY(!(m_bits & 1));
}
ALWAYS_INLINE NonnullRefPtr(NonnullRefPtr&& other)
: m_bits((FlatPtr)&other.leak_ref())
{
VERIFY(!(m_bits & 1));
}
template<typename U>
ALWAYS_INLINE NonnullRefPtr(NonnullRefPtr<U>&& other)
: m_bits((FlatPtr)&other.leak_ref())
{
VERIFY(!(m_bits & 1));
}
ALWAYS_INLINE NonnullRefPtr(const NonnullRefPtr& other)
: m_bits((FlatPtr)other.add_ref())
{
VERIFY(!(m_bits & 1));
}
template<typename U>
ALWAYS_INLINE NonnullRefPtr(const NonnullRefPtr<U>& other)
: m_bits((FlatPtr)other.add_ref())
{
VERIFY(!(m_bits & 1));
}
ALWAYS_INLINE ~NonnullRefPtr()
{
assign(nullptr);
#ifdef SANITIZE_PTRS
if constexpr (sizeof(T*) == 8)
m_bits.store(0xb0b0b0b0b0b0b0b0, AK::MemoryOrder::memory_order_relaxed);
else
m_bits.store(0xb0b0b0b0, AK::MemoryOrder::memory_order_relaxed);
#endif
}
template<typename U>
NonnullRefPtr(const OwnPtr<U>&) = delete;
template<typename U>
NonnullRefPtr& operator=(const OwnPtr<U>&) = delete;
template<typename U>
NonnullRefPtr(const RefPtr<U>&) = delete;
template<typename U>
NonnullRefPtr& operator=(const RefPtr<U>&) = delete;
NonnullRefPtr(const RefPtr<T>&) = delete;
NonnullRefPtr& operator=(const RefPtr<T>&) = delete;
NonnullRefPtr& operator=(const NonnullRefPtr& other)
{
if (this != &other)
assign(other.add_ref());
return *this;
}
template<typename U>
NonnullRefPtr& operator=(const NonnullRefPtr<U>& other)
{
assign(other.add_ref());
return *this;
}
ALWAYS_INLINE NonnullRefPtr& operator=(NonnullRefPtr&& other)
{
if (this != &other)
assign(&other.leak_ref());
return *this;
}
template<typename U>
NonnullRefPtr& operator=(NonnullRefPtr<U>&& other)
{
assign(&other.leak_ref());
return *this;
}
NonnullRefPtr& operator=(const T& object)
{
const_cast<T&>(object).ref();
assign(const_cast<T*>(&object));
return *this;
}
[[nodiscard]] ALWAYS_INLINE T& leak_ref()
{
T* ptr = exchange(nullptr);
VERIFY(ptr);
return *ptr;
}
ALWAYS_INLINE T* ptr()
{
return as_nonnull_ptr();
}
ALWAYS_INLINE const T* ptr() const
{
return as_nonnull_ptr();
}
ALWAYS_INLINE T* operator->()
{
return as_nonnull_ptr();
}
ALWAYS_INLINE const T* operator->() const
{
return as_nonnull_ptr();
}
ALWAYS_INLINE T& operator*()
{
return *as_nonnull_ptr();
}
ALWAYS_INLINE const T& operator*() const
{
return *as_nonnull_ptr();
}
ALWAYS_INLINE operator T*()
{
return as_nonnull_ptr();
}
ALWAYS_INLINE operator const T*() const
{
return as_nonnull_ptr();
}
ALWAYS_INLINE operator T&()
{
return *as_nonnull_ptr();
}
ALWAYS_INLINE operator const T&() const
{
return *as_nonnull_ptr();
}
operator bool() const = delete;
bool operator!() const = delete;
void swap(NonnullRefPtr& other)
{
if (this == &other)
return;
// NOTE: swap is not atomic!
T* other_ptr = other.exchange(nullptr);
T* ptr = exchange(other_ptr);
other.exchange(ptr);
}
template<typename U>
void swap(NonnullRefPtr<U>& other)
{
// NOTE: swap is not atomic!
U* other_ptr = other.exchange(nullptr);
T* ptr = exchange(other_ptr);
other.exchange(ptr);
}
private:
NonnullRefPtr() = delete;
ALWAYS_INLINE T* as_ptr() const
{
return (T*)(m_bits.load(AK::MemoryOrder::memory_order_relaxed) & ~(FlatPtr)1);
}
ALWAYS_INLINE T* as_nonnull_ptr() const
{
T* ptr = (T*)(m_bits.load(AK::MemoryOrder::memory_order_relaxed) & ~(FlatPtr)1);
VERIFY(ptr);
return ptr;
}
template<typename F>
void do_while_locked(F f) const
{
#ifdef KERNEL
// We don't want to be pre-empted while we have the lock bit set
Kernel::ScopedCritical critical;
#endif
FlatPtr bits;
for (;;) {
bits = m_bits.fetch_or(1, AK::MemoryOrder::memory_order_acq_rel);
if (!(bits & 1))
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
VERIFY(!(bits & 1));
f((T*)bits);
m_bits.store(bits, AK::MemoryOrder::memory_order_release);
}
ALWAYS_INLINE void assign(T* new_ptr)
{
T* prev_ptr = exchange(new_ptr);
unref_if_not_null(prev_ptr);
}
ALWAYS_INLINE T* exchange(T* new_ptr)
{
VERIFY(!((FlatPtr)new_ptr & 1));
#ifdef KERNEL
// We don't want to be pre-empted while we have the lock bit set
Kernel::ScopedCritical critical;
#endif
// Only exchange while not locked
FlatPtr expected = m_bits.load(AK::MemoryOrder::memory_order_relaxed);
for (;;) {
expected &= ~(FlatPtr)1; // only if lock bit is not set
if (m_bits.compare_exchange_strong(expected, (FlatPtr)new_ptr, AK::MemoryOrder::memory_order_acq_rel))
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
VERIFY(!(expected & 1));
return (T*)expected;
}
T* add_ref() const
{
#ifdef KERNEL
// We don't want to be pre-empted while we have the lock bit set
Kernel::ScopedCritical critical;
#endif
// Lock the pointer
FlatPtr expected = m_bits.load(AK::MemoryOrder::memory_order_relaxed);
for (;;) {
expected &= ~(FlatPtr)1; // only if lock bit is not set
if (m_bits.compare_exchange_strong(expected, expected | 1, AK::MemoryOrder::memory_order_acq_rel))
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
// Add a reference now that we locked the pointer
ref_if_not_null((T*)expected);
// Unlock the pointer again
m_bits.store(expected, AK::MemoryOrder::memory_order_release);
return (T*)expected;
}
mutable Atomic<FlatPtr> m_bits { 0 };
};
template<typename T>
inline NonnullRefPtr<T> adopt_ref(T& object)
{
return NonnullRefPtr<T>(NonnullRefPtr<T>::Adopt, object);
}
template<typename T>
struct Formatter<NonnullRefPtr<T>> : Formatter<const T*> {
void format(FormatBuilder& builder, const NonnullRefPtr<T>& value)
{
Formatter<const T*>::format(builder, value.ptr());
}
};
template<typename T, typename U>
inline void swap(NonnullRefPtr<T>& a, NonnullRefPtr<U>& b)
{
a.swap(b);
}
}
template<typename T>
struct Traits<NonnullRefPtr<T>> : public GenericTraits<NonnullRefPtr<T>> {
using PeekType = T*;
using ConstPeekType = const T*;
static unsigned hash(const NonnullRefPtr<T>& p) { return ptr_hash(p.ptr()); }
static bool equals(const NonnullRefPtr<T>& a, const NonnullRefPtr<T>& b) { return a.ptr() == b.ptr(); }
};
using AK::adopt_ref;
using AK::NonnullRefPtr;