ladybird/Kernel/Library/LockRefPtr.h
Tim Schumacher a2f60911fe AK: Rename GenericTraits to DefaultTraits
This feels like a more fitting name for something that provides the
default values for Traits.
2023-11-09 10:05:51 -05:00

529 lines
16 KiB
C++

/*
* 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/Error.h>
#include <AK/Format.h>
#include <AK/StdLibExtras.h>
#include <AK/Traits.h>
#include <AK/Types.h>
#include <Kernel/Library/NonnullLockRefPtr.h>
#ifdef KERNEL
# include <Kernel/Arch/Processor.h>
# include <Kernel/Library/ScopedCritical.h>
#endif
#define LOCKREFPTR_SCRUB_BYTE 0xa0
namespace AK {
template<typename T>
struct LockRefPtrTraits {
ALWAYS_INLINE static T* as_ptr(FlatPtr bits)
{
return (T*)(bits & ~(FlatPtr)1);
}
ALWAYS_INLINE static FlatPtr as_bits(T* ptr)
{
VERIFY(((FlatPtr)ptr & 1) == 0);
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) == 0;
}
ALWAYS_INLINE static FlatPtr exchange(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
{
// Only exchange when lock is not held
VERIFY((new_value & 1) == 0);
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
VERIFY((new_value & 1) == 0);
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 LockRefPtr 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) == 0)
break;
#ifdef KERNEL
Kernel::Processor::wait_check();
#endif
}
VERIFY((bits & 1) == 0);
return bits;
}
ALWAYS_INLINE static void unlock(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
{
VERIFY((new_value & 1) == 0);
atomic_var.store(new_value, AK::MemoryOrder::memory_order_release);
}
static constexpr FlatPtr default_null_value = 0;
using NullType = nullptr_t;
};
template<typename T, typename PtrTraits>
class [[nodiscard]] LockRefPtr {
template<typename U, typename P>
friend class LockRefPtr;
template<typename U>
friend class LockWeakPtr;
public:
enum AdoptTag {
Adopt
};
LockRefPtr() = default;
LockRefPtr(T const* ptr)
: m_bits(PtrTraits::as_bits(const_cast<T*>(ptr)))
{
ref_if_not_null(const_cast<T*>(ptr));
}
LockRefPtr(T const& object)
: m_bits(PtrTraits::as_bits(const_cast<T*>(&object)))
{
T* ptr = const_cast<T*>(&object);
VERIFY(ptr);
VERIFY(!is_null());
ptr->ref();
}
LockRefPtr(AdoptTag, T& object)
: m_bits(PtrTraits::as_bits(&object))
{
VERIFY(!is_null());
}
LockRefPtr(LockRefPtr&& other)
: m_bits(other.leak_ref_raw())
{
}
ALWAYS_INLINE LockRefPtr(NonnullLockRefPtr<T> const& other)
: m_bits(PtrTraits::as_bits(const_cast<T*>(other.add_ref())))
{
}
template<typename U>
ALWAYS_INLINE LockRefPtr(NonnullLockRefPtr<U> const& other)
requires(IsConvertible<U*, T*>)
: m_bits(PtrTraits::as_bits(const_cast<U*>(other.add_ref())))
{
}
template<typename U>
ALWAYS_INLINE LockRefPtr(NonnullLockRefPtr<U>&& other)
requires(IsConvertible<U*, T*>)
: m_bits(PtrTraits::as_bits(&other.leak_ref()))
{
VERIFY(!is_null());
}
template<typename U, typename P = LockRefPtrTraits<U>>
LockRefPtr(LockRefPtr<U, P>&& other)
requires(IsConvertible<U*, T*>)
: m_bits(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()))
{
}
LockRefPtr(LockRefPtr const& other)
: m_bits(other.add_ref_raw())
{
}
template<typename U, typename P = LockRefPtrTraits<U>>
LockRefPtr(LockRefPtr<U, P> const& other)
requires(IsConvertible<U*, T*>)
: m_bits(other.add_ref_raw())
{
}
ALWAYS_INLINE ~LockRefPtr()
{
clear();
#ifdef SANITIZE_PTRS
m_bits.store(explode_byte(LOCKREFPTR_SCRUB_BYTE), AK::MemoryOrder::memory_order_relaxed);
#endif
}
template<typename U>
LockRefPtr(OwnPtr<U> const&) = delete;
template<typename U>
LockRefPtr& operator=(OwnPtr<U> const&) = delete;
void swap(LockRefPtr& 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 = LockRefPtrTraits<U>>
void swap(LockRefPtr<U, P>& other)
requires(IsConvertible<U*, T*>)
{
// 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 LockRefPtr& operator=(LockRefPtr&& other)
{
if (this != &other)
assign_raw(other.leak_ref_raw());
return *this;
}
template<typename U, typename P = LockRefPtrTraits<U>>
ALWAYS_INLINE LockRefPtr& operator=(LockRefPtr<U, P>&& other)
requires(IsConvertible<U*, T*>)
{
assign_raw(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()));
return *this;
}
template<typename U>
ALWAYS_INLINE LockRefPtr& operator=(NonnullLockRefPtr<U>&& other)
requires(IsConvertible<U*, T*>)
{
assign_raw(PtrTraits::as_bits(&other.leak_ref()));
return *this;
}
ALWAYS_INLINE LockRefPtr& operator=(NonnullLockRefPtr<T> const& other)
{
assign_raw(PtrTraits::as_bits(other.add_ref()));
return *this;
}
template<typename U>
ALWAYS_INLINE LockRefPtr& operator=(NonnullLockRefPtr<U> const& other)
requires(IsConvertible<U*, T*>)
{
assign_raw(PtrTraits::as_bits(other.add_ref()));
return *this;
}
ALWAYS_INLINE LockRefPtr& operator=(LockRefPtr const& other)
{
if (this != &other)
assign_raw(other.add_ref_raw());
return *this;
}
template<typename U>
ALWAYS_INLINE LockRefPtr& operator=(LockRefPtr<U> const& other)
requires(IsConvertible<U*, T*>)
{
assign_raw(other.add_ref_raw());
return *this;
}
ALWAYS_INLINE LockRefPtr& operator=(T const* ptr)
{
ref_if_not_null(const_cast<T*>(ptr));
assign_raw(PtrTraits::as_bits(const_cast<T*>(ptr)));
return *this;
}
ALWAYS_INLINE LockRefPtr& operator=(T const& object)
{
const_cast<T&>(object).ref();
assign_raw(PtrTraits::as_bits(const_cast<T*>(&object)));
return *this;
}
LockRefPtr& operator=(nullptr_t)
{
clear();
return *this;
}
ALWAYS_INLINE bool assign_if_null(LockRefPtr&& other)
{
if (this == &other)
return is_null();
return PtrTraits::exchange_if_null(m_bits, other.leak_ref_raw());
}
template<typename U, typename P = LockRefPtrTraits<U>>
ALWAYS_INLINE bool assign_if_null(LockRefPtr<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);
}
NonnullLockRefPtr<T> release_nonnull()
{
FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
VERIFY(!PtrTraits::is_null(bits));
return NonnullLockRefPtr<T>(NonnullLockRefPtr<T>::Adopt, *PtrTraits::as_ptr(bits));
}
ALWAYS_INLINE T* ptr() { return as_ptr(); }
ALWAYS_INLINE T const* ptr() const { return as_ptr(); }
ALWAYS_INLINE T* operator->()
{
return as_nonnull_ptr();
}
ALWAYS_INLINE T const* operator->() const
{
return as_nonnull_ptr();
}
ALWAYS_INLINE T& operator*()
{
return *as_nonnull_ptr();
}
ALWAYS_INLINE T const& operator*() const
{
return *as_nonnull_ptr();
}
ALWAYS_INLINE operator T const*() const { return as_ptr(); }
ALWAYS_INLINE operator T*() { return as_ptr(); }
ALWAYS_INLINE operator bool() { return !is_null(); }
bool operator==(nullptr_t) const { return is_null(); }
bool operator!=(nullptr_t) const { return !is_null(); }
bool operator==(LockRefPtr const& other) const { return as_ptr() == other.as_ptr(); }
bool operator!=(LockRefPtr const& other) const { return as_ptr() != other.as_ptr(); }
bool operator==(LockRefPtr& other) { return as_ptr() == other.as_ptr(); }
bool operator!=(LockRefPtr& other) { return as_ptr() != other.as_ptr(); }
bool operator==(T const* other) const { return as_ptr() == other; }
bool operator!=(T const* 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 PtrTraits::NullType null_value() const
requires(IsSame<U, T> && !IsNullPointer<typename PtrTraits::NullType>)
{
// make sure we are holding a null value
FlatPtr bits = m_bits.load(AK::MemoryOrder::memory_order_relaxed);
VERIFY(PtrTraits::is_null(bits));
return PtrTraits::to_null_value(bits);
}
template<typename U = T>
void set_null_value(typename PtrTraits::NullType value)
requires(IsSame<U, T> && !IsNullPointer<typename PtrTraits::NullType>)
{
// make sure that new null value would be interpreted as a null value
FlatPtr bits = PtrTraits::from_null_value(value);
VERIFY(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 LockRefPtr, 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
{
VERIFY(!PtrTraits::is_null(bits));
return PtrTraits::as_ptr(bits);
}
mutable Atomic<FlatPtr> m_bits { PtrTraits::default_null_value };
};
template<typename T>
struct Formatter<LockRefPtr<T>> : Formatter<T const*> {
ErrorOr<void> format(FormatBuilder& builder, LockRefPtr<T> const& value)
{
return Formatter<T const*>::format(builder, value.ptr());
}
};
template<typename T>
struct Traits<LockRefPtr<T>> : public DefaultTraits<LockRefPtr<T>> {
using PeekType = T*;
using ConstPeekType = T const*;
static unsigned hash(LockRefPtr<T> const& p) { return ptr_hash(p.ptr()); }
static bool equals(LockRefPtr<T> const& a, LockRefPtr<T> const& b) { return a.ptr() == b.ptr(); }
};
template<typename T, typename U>
inline NonnullLockRefPtr<T> static_ptr_cast(NonnullLockRefPtr<U> const& ptr)
{
return NonnullLockRefPtr<T>(static_cast<T const&>(*ptr));
}
template<typename T, typename U, typename PtrTraits = LockRefPtrTraits<T>>
inline LockRefPtr<T> static_ptr_cast(LockRefPtr<U> const& ptr)
{
return LockRefPtr<T, PtrTraits>(static_cast<T const*>(ptr.ptr()));
}
template<typename T, typename PtrTraitsT, typename U, typename PtrTraitsU>
inline void swap(LockRefPtr<T, PtrTraitsT>& a, LockRefPtr<U, PtrTraitsU>& b)
requires(IsConvertible<U*, T*>)
{
a.swap(b);
}
template<typename T>
inline LockRefPtr<T> adopt_lock_ref_if_nonnull(T* object)
{
if (object)
return LockRefPtr<T>(LockRefPtr<T>::Adopt, *object);
return {};
}
template<typename T, class... Args>
requires(IsConstructible<T, Args...>) inline ErrorOr<NonnullLockRefPtr<T>> try_make_lock_ref_counted(Args&&... args)
{
return adopt_nonnull_lock_ref_or_enomem(new (nothrow) T(forward<Args>(args)...));
}
// FIXME: Remove once P0960R3 is available in Clang.
template<typename T, class... Args>
inline ErrorOr<NonnullLockRefPtr<T>> try_make_lock_ref_counted(Args&&... args)
{
return adopt_nonnull_lock_ref_or_enomem(new (nothrow) T { forward<Args>(args)... });
}
template<typename T>
inline ErrorOr<NonnullLockRefPtr<T>> adopt_nonnull_lock_ref_or_enomem(T* object)
{
auto result = adopt_lock_ref_if_nonnull(object);
if (!result)
return Error::from_errno(ENOMEM);
return result.release_nonnull();
}
}
using AK::adopt_lock_ref_if_nonnull;
using AK::LockRefPtr;
using AK::static_ptr_cast;
using AK::try_make_lock_ref_counted;
#ifdef KERNEL
using AK::adopt_nonnull_lock_ref_or_enomem;
#endif