ladybird/AK/RefPtr.h
Lenny Maiorani e6f907a155 AK: Simplify constructors and conversions from nullptr_t
Problem:
- Many constructors are defined as `{}` rather than using the ` =
  default` compiler-provided constructor.
- Some types provide an implicit conversion operator from `nullptr_t`
  instead of requiring the caller to default construct. This violates
  the C++ Core Guidelines suggestion to declare single-argument
  constructors explicit
  (https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c46-by-default-declare-single-argument-constructors-explicit).

Solution:
- Change default constructors to use the compiler-provided default
  constructor.
- Remove implicit conversion operators from `nullptr_t` and change
  usage to enforce type consistency without conversion.
2021-01-12 09:11:45 +01:00

499 lines
15 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/Atomic.h>
#include <AK/LogStream.h>
#include <AK/NonnullRefPtr.h>
#include <AK/StdLibExtras.h>
#include <AK/Traits.h>
#include <AK/Types.h>
#ifdef KERNEL
# include <Kernel/Arch/i386/CPU.h>
#endif
namespace AK {
template<typename T>
class OwnPtr;
template<typename T>
struct RefPtrTraits {
ALWAYS_INLINE static T* as_ptr(FlatPtr bits)
{
return (T*)(bits & ~(FlatPtr)1);
}
ALWAYS_INLINE static FlatPtr as_bits(T* ptr)
{
ASSERT(!((FlatPtr)ptr & 1));
return (FlatPtr)ptr;
}
template<typename U, typename PtrTraits>
ALWAYS_INLINE static FlatPtr convert_from(FlatPtr bits)
{
if (PtrTraits::is_null(bits))
return default_null_value;
return as_bits(PtrTraits::as_ptr(bits));
}
ALWAYS_INLINE static bool is_null(FlatPtr bits)
{
return !(bits & ~(FlatPtr)1);
}
ALWAYS_INLINE static FlatPtr exchange(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
{
// Only exchange when lock is not held
ASSERT(!(new_value & 1));
FlatPtr expected = atomic_var.load(AK::MemoryOrder::memory_order_relaxed);
for (;;) {
expected &= ~(FlatPtr)1; // only if lock bit is not set
if (atomic_var.compare_exchange_strong(expected, new_value, AK::MemoryOrder::memory_order_acq_rel))
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
return expected;
}
ALWAYS_INLINE static bool exchange_if_null(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
{
// Only exchange when lock is not held
ASSERT(!(new_value & 1));
for (;;) {
FlatPtr expected = default_null_value; // only if lock bit is not set
if (atomic_var.compare_exchange_strong(expected, new_value, AK::MemoryOrder::memory_order_acq_rel))
break;
if (!is_null(expected))
return false;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
return true;
}
ALWAYS_INLINE static FlatPtr lock(Atomic<FlatPtr>& atomic_var)
{
// This sets the lock bit atomically, preventing further modifications.
// This is important when e.g. copying a RefPtr where the source
// might be released and freed too quickly. This allows us
// to temporarily lock the pointer so we can add a reference, then
// unlock it
FlatPtr bits;
for (;;) {
bits = atomic_var.fetch_or(1, AK::MemoryOrder::memory_order_acq_rel);
if (!(bits & 1))
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
ASSERT(!(bits & 1));
return bits;
}
ALWAYS_INLINE static void unlock(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
{
ASSERT(!(new_value & 1));
atomic_var.store(new_value, AK::MemoryOrder::memory_order_release);
}
static constexpr FlatPtr default_null_value = 0;
using NullType = std::nullptr_t;
};
template<typename T, typename PtrTraits>
class RefPtr {
template<typename U, typename P>
friend class RefPtr;
template<typename U>
friend class WeakPtr;
public:
enum AdoptTag {
Adopt
};
RefPtr() = default;
RefPtr(const T* ptr)
: m_bits(PtrTraits::as_bits(const_cast<T*>(ptr)))
{
ref_if_not_null(const_cast<T*>(ptr));
}
RefPtr(const T& object)
: m_bits(PtrTraits::as_bits(const_cast<T*>(&object)))
{
T* ptr = const_cast<T*>(&object);
ASSERT(ptr);
ASSERT(!is_null());
ptr->ref();
}
RefPtr(AdoptTag, T& object)
: m_bits(PtrTraits::as_bits(&object))
{
ASSERT(!is_null());
}
RefPtr(RefPtr&& other)
: m_bits(other.leak_ref_raw())
{
}
ALWAYS_INLINE RefPtr(const NonnullRefPtr<T>& other)
: m_bits(PtrTraits::as_bits(const_cast<T*>(other.add_ref())))
{
}
template<typename U>
ALWAYS_INLINE RefPtr(const NonnullRefPtr<U>& other)
: m_bits(PtrTraits::as_bits(const_cast<U*>(other.add_ref())))
{
}
template<typename U>
ALWAYS_INLINE RefPtr(NonnullRefPtr<U>&& other)
: m_bits(PtrTraits::as_bits(&other.leak_ref()))
{
ASSERT(!is_null());
}
template<typename U, typename P = RefPtrTraits<U>>
RefPtr(RefPtr<U, P>&& other)
: m_bits(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()))
{
}
RefPtr(const RefPtr& other)
: m_bits(other.add_ref_raw())
{
}
template<typename U, typename P = RefPtrTraits<U>>
RefPtr(const RefPtr<U, P>& other)
: m_bits(other.add_ref_raw())
{
}
ALWAYS_INLINE ~RefPtr()
{
clear();
#ifdef SANITIZE_PTRS
if constexpr (sizeof(T*) == 8)
m_bits.store(0xe0e0e0e0e0e0e0e0, AK::MemoryOrder::memory_order_relaxed);
else
m_bits.store(0xe0e0e0e0, AK::MemoryOrder::memory_order_relaxed);
#endif
}
template<typename U>
RefPtr(const OwnPtr<U>&) = delete;
template<typename U>
RefPtr& operator=(const OwnPtr<U>&) = delete;
void swap(RefPtr& other)
{
if (this == &other)
return;
// NOTE: swap is not atomic!
FlatPtr other_bits = PtrTraits::exchange(other.m_bits, PtrTraits::default_null_value);
FlatPtr bits = PtrTraits::exchange(m_bits, other_bits);
PtrTraits::exchange(other.m_bits, bits);
}
template<typename U, typename P = RefPtrTraits<U>>
void swap(RefPtr<U, P>& other)
{
// NOTE: swap is not atomic!
FlatPtr other_bits = P::exchange(other.m_bits, P::default_null_value);
FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::template convert_from<U, P>(other_bits));
P::exchange(other.m_bits, P::template convert_from<U, P>(bits));
}
ALWAYS_INLINE RefPtr& operator=(RefPtr&& other)
{
if (this != &other)
assign_raw(other.leak_ref_raw());
return *this;
}
template<typename U, typename P = RefPtrTraits<U>>
ALWAYS_INLINE RefPtr& operator=(RefPtr<U, P>&& other)
{
assign_raw(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()));
return *this;
}
template<typename U>
ALWAYS_INLINE RefPtr& operator=(NonnullRefPtr<U>&& other)
{
assign_raw(PtrTraits::as_bits(&other.leak_ref()));
return *this;
}
ALWAYS_INLINE RefPtr& operator=(const NonnullRefPtr<T>& other)
{
assign_raw(PtrTraits::as_bits(other.add_ref()));
return *this;
}
template<typename U>
ALWAYS_INLINE RefPtr& operator=(const NonnullRefPtr<U>& other)
{
assign_raw(PtrTraits::as_bits(other.add_ref()));
return *this;
}
ALWAYS_INLINE RefPtr& operator=(const RefPtr& other)
{
if (this != &other)
assign_raw(other.add_ref_raw());
return *this;
}
template<typename U>
ALWAYS_INLINE RefPtr& operator=(const RefPtr<U>& other)
{
assign_raw(other.add_ref_raw());
return *this;
}
ALWAYS_INLINE RefPtr& operator=(const T* ptr)
{
ref_if_not_null(const_cast<T*>(ptr));
assign_raw(PtrTraits::as_bits(const_cast<T*>(ptr)));
return *this;
}
ALWAYS_INLINE RefPtr& operator=(const T& object)
{
const_cast<T&>(object).ref();
assign_raw(PtrTraits::as_bits(const_cast<T*>(&object)));
return *this;
}
RefPtr& operator=(std::nullptr_t)
{
clear();
return *this;
}
ALWAYS_INLINE bool assign_if_null(RefPtr&& other)
{
if (this == &other)
return is_null();
return PtrTraits::exchange_if_null(m_bits, other.leak_ref_raw());
}
template<typename U, typename P = RefPtrTraits<U>>
ALWAYS_INLINE bool assign_if_null(RefPtr<U, P>&& other)
{
if (this == &other)
return is_null();
return PtrTraits::exchange_if_null(m_bits, PtrTraits::template convert_from<U, P>(other.leak_ref_raw()));
}
ALWAYS_INLINE void clear()
{
assign_raw(PtrTraits::default_null_value);
}
bool operator!() const { return PtrTraits::is_null(m_bits.load(AK::MemoryOrder::memory_order_relaxed)); }
[[nodiscard]] T* leak_ref()
{
FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
return PtrTraits::as_ptr(bits);
}
NonnullRefPtr<T> release_nonnull()
{
FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
ASSERT(!PtrTraits::is_null(bits));
return NonnullRefPtr<T>(NonnullRefPtr<T>::Adopt, *PtrTraits::as_ptr(bits));
}
ALWAYS_INLINE T* ptr() { return as_ptr(); }
ALWAYS_INLINE const T* ptr() const { return as_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 const T*() const { return as_ptr(); }
ALWAYS_INLINE operator T*() { return as_ptr(); }
ALWAYS_INLINE operator bool() { return !is_null(); }
bool operator==(std::nullptr_t) const { return is_null(); }
bool operator!=(std::nullptr_t) const { return !is_null(); }
bool operator==(const RefPtr& other) const { return as_ptr() == other.as_ptr(); }
bool operator!=(const RefPtr& other) const { return as_ptr() != other.as_ptr(); }
bool operator==(RefPtr& other) { return as_ptr() == other.as_ptr(); }
bool operator!=(RefPtr& other) { return as_ptr() != other.as_ptr(); }
bool operator==(const T* other) const { return as_ptr() == other; }
bool operator!=(const T* other) const { return as_ptr() != other; }
bool operator==(T* other) { return as_ptr() == other; }
bool operator!=(T* other) { return as_ptr() != other; }
ALWAYS_INLINE bool is_null() const { return PtrTraits::is_null(m_bits.load(AK::MemoryOrder::memory_order_relaxed)); }
template<typename U = T, typename EnableIf<IsSame<U, T>::value && !IsNullPointer<typename PtrTraits::NullType>::value>::Type* = nullptr>
typename PtrTraits::NullType null_value() const
{
// make sure we are holding a null value
FlatPtr bits = m_bits.load(AK::MemoryOrder::memory_order_relaxed);
ASSERT(PtrTraits::is_null(bits));
return PtrTraits::to_null_value(bits);
}
template<typename U = T, typename EnableIf<IsSame<U, T>::value && !IsNullPointer<typename PtrTraits::NullType>::value>::Type* = nullptr>
void set_null_value(typename PtrTraits::NullType value)
{
// make sure that new null value would be interpreted as a null value
FlatPtr bits = PtrTraits::from_null_value(value);
ASSERT(PtrTraits::is_null(bits));
assign_raw(bits);
}
private:
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 = PtrTraits::lock(m_bits);
T* ptr = PtrTraits::as_ptr(bits);
f(ptr);
PtrTraits::unlock(m_bits, bits);
}
[[nodiscard]] ALWAYS_INLINE FlatPtr leak_ref_raw()
{
return PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
}
[[nodiscard]] ALWAYS_INLINE FlatPtr add_ref_raw() const
{
#ifdef KERNEL
// We don't want to be pre-empted while we have the lock bit set
Kernel::ScopedCritical critical;
#endif
// This prevents a race condition between thread A and B:
// 1. Thread A copies RefPtr, e.g. through assignment or copy constructor,
// gets the pointer from source, but is pre-empted before adding
// another reference
// 2. Thread B calls clear, leak_ref, or release_nonnull on source, and
// then drops the last reference, causing the object to be deleted
// 3. Thread A finishes step #1 by attempting to add a reference to
// the object that was already deleted in step #2
FlatPtr bits = PtrTraits::lock(m_bits);
if (T* ptr = PtrTraits::as_ptr(bits))
ptr->ref();
PtrTraits::unlock(m_bits, bits);
return bits;
}
ALWAYS_INLINE void assign_raw(FlatPtr bits)
{
FlatPtr prev_bits = PtrTraits::exchange(m_bits, bits);
unref_if_not_null(PtrTraits::as_ptr(prev_bits));
}
ALWAYS_INLINE T* as_ptr() const
{
return PtrTraits::as_ptr(m_bits.load(AK::MemoryOrder::memory_order_relaxed));
}
ALWAYS_INLINE T* as_nonnull_ptr() const
{
return as_nonnull_ptr(m_bits.load(AK::MemoryOrder::memory_order_relaxed));
}
ALWAYS_INLINE T* as_nonnull_ptr(FlatPtr bits) const
{
ASSERT(!PtrTraits::is_null(bits));
return PtrTraits::as_ptr(bits);
}
mutable Atomic<FlatPtr> m_bits { PtrTraits::default_null_value };
};
template<typename T, typename PtrTraits = RefPtrTraits<T>>
inline const LogStream& operator<<(const LogStream& stream, const RefPtr<T, PtrTraits>& value)
{
return stream << value.ptr();
}
template<typename T>
struct Traits<RefPtr<T>> : public GenericTraits<RefPtr<T>> {
using PeekType = const T*;
static unsigned hash(const RefPtr<T>& p) { return ptr_hash(p.ptr()); }
static bool equals(const RefPtr<T>& a, const RefPtr<T>& b) { return a.ptr() == b.ptr(); }
};
template<typename T, typename U>
inline NonnullRefPtr<T> static_ptr_cast(const NonnullRefPtr<U>& ptr)
{
return NonnullRefPtr<T>(static_cast<const T&>(*ptr));
}
template<typename T, typename U, typename PtrTraits = RefPtrTraits<T>>
inline RefPtr<T> static_ptr_cast(const RefPtr<U>& ptr)
{
return RefPtr<T, PtrTraits>(static_cast<const T*>(ptr.ptr()));
}
template<typename T, typename PtrTraitsT, typename U, typename PtrTraitsU>
inline void swap(RefPtr<T, PtrTraitsT>& a, RefPtr<U, PtrTraitsU>& b)
{
a.swap(b);
}
}
using AK::RefPtr;
using AK::static_ptr_cast;