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https://github.com/RGBCube/serenity
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480 lines
14 KiB
C++
480 lines
14 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Atomic.h>
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#include <AK/Format.h>
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#include <AK/NonnullRefPtr.h>
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#include <AK/StdLibExtras.h>
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#include <AK/Traits.h>
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#include <AK/Types.h>
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#ifdef KERNEL
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# include <Kernel/Arch/x86/CPU.h>
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#endif
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namespace AK {
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template<typename T>
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class OwnPtr;
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template<typename T>
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struct RefPtrTraits {
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ALWAYS_INLINE static T* as_ptr(FlatPtr bits)
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{
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return (T*)(bits & ~(FlatPtr)1);
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}
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ALWAYS_INLINE static FlatPtr as_bits(T* ptr)
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{
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VERIFY(!((FlatPtr)ptr & 1));
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return (FlatPtr)ptr;
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}
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template<typename U, typename PtrTraits>
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ALWAYS_INLINE static FlatPtr convert_from(FlatPtr bits)
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{
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if (PtrTraits::is_null(bits))
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return default_null_value;
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return as_bits(PtrTraits::as_ptr(bits));
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}
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ALWAYS_INLINE static bool is_null(FlatPtr bits)
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{
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return !(bits & ~(FlatPtr)1);
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}
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ALWAYS_INLINE static FlatPtr exchange(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
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{
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// Only exchange when lock is not held
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VERIFY(!(new_value & 1));
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FlatPtr expected = atomic_var.load(AK::MemoryOrder::memory_order_relaxed);
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for (;;) {
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expected &= ~(FlatPtr)1; // only if lock bit is not set
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if (atomic_var.compare_exchange_strong(expected, new_value, AK::MemoryOrder::memory_order_acq_rel))
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break;
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#ifdef KERNEL
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Kernel::Processor::wait_check();
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#endif
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}
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return expected;
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}
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ALWAYS_INLINE static bool exchange_if_null(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
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{
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// Only exchange when lock is not held
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VERIFY(!(new_value & 1));
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for (;;) {
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FlatPtr expected = default_null_value; // only if lock bit is not set
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if (atomic_var.compare_exchange_strong(expected, new_value, AK::MemoryOrder::memory_order_acq_rel))
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break;
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if (!is_null(expected))
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return false;
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#ifdef KERNEL
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Kernel::Processor::wait_check();
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#endif
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}
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return true;
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}
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ALWAYS_INLINE static FlatPtr lock(Atomic<FlatPtr>& atomic_var)
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{
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// This sets the lock bit atomically, preventing further modifications.
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// This is important when e.g. copying a RefPtr where the source
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// might be released and freed too quickly. This allows us
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// to temporarily lock the pointer so we can add a reference, then
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// unlock it
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FlatPtr bits;
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for (;;) {
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bits = atomic_var.fetch_or(1, AK::MemoryOrder::memory_order_acq_rel);
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if (!(bits & 1))
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break;
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#ifdef KERNEL
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Kernel::Processor::wait_check();
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#endif
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}
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VERIFY(!(bits & 1));
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return bits;
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}
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ALWAYS_INLINE static void unlock(Atomic<FlatPtr>& atomic_var, FlatPtr new_value)
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{
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VERIFY(!(new_value & 1));
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atomic_var.store(new_value, AK::MemoryOrder::memory_order_release);
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}
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static constexpr FlatPtr default_null_value = 0;
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using NullType = std::nullptr_t;
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};
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template<typename T, typename PtrTraits>
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class RefPtr {
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template<typename U, typename P>
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friend class RefPtr;
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template<typename U>
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friend class WeakPtr;
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public:
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enum AdoptTag {
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Adopt
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};
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RefPtr() = default;
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RefPtr(const T* ptr)
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: m_bits(PtrTraits::as_bits(const_cast<T*>(ptr)))
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{
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ref_if_not_null(const_cast<T*>(ptr));
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}
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RefPtr(const T& object)
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: m_bits(PtrTraits::as_bits(const_cast<T*>(&object)))
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{
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T* ptr = const_cast<T*>(&object);
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VERIFY(ptr);
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VERIFY(!is_null());
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ptr->ref();
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}
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RefPtr(AdoptTag, T& object)
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: m_bits(PtrTraits::as_bits(&object))
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{
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VERIFY(!is_null());
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}
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RefPtr(RefPtr&& other)
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: m_bits(other.leak_ref_raw())
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{
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}
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ALWAYS_INLINE RefPtr(const NonnullRefPtr<T>& other)
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: m_bits(PtrTraits::as_bits(const_cast<T*>(other.add_ref())))
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{
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}
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template<typename U>
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ALWAYS_INLINE RefPtr(const NonnullRefPtr<U>& other)
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: m_bits(PtrTraits::as_bits(const_cast<U*>(other.add_ref())))
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{
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}
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template<typename U>
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ALWAYS_INLINE RefPtr(NonnullRefPtr<U>&& other)
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: m_bits(PtrTraits::as_bits(&other.leak_ref()))
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{
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VERIFY(!is_null());
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}
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template<typename U, typename P = RefPtrTraits<U>>
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RefPtr(RefPtr<U, P>&& other)
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: m_bits(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()))
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{
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}
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RefPtr(const RefPtr& other)
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: m_bits(other.add_ref_raw())
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{
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}
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template<typename U, typename P = RefPtrTraits<U>>
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RefPtr(const RefPtr<U, P>& other)
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: m_bits(other.add_ref_raw())
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{
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}
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ALWAYS_INLINE ~RefPtr()
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{
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clear();
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#ifdef SANITIZE_PTRS
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if constexpr (sizeof(T*) == 8)
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m_bits.store(0xe0e0e0e0e0e0e0e0, AK::MemoryOrder::memory_order_relaxed);
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else
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m_bits.store(0xe0e0e0e0, AK::MemoryOrder::memory_order_relaxed);
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#endif
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}
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template<typename U>
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RefPtr(const OwnPtr<U>&) = delete;
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template<typename U>
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RefPtr& operator=(const OwnPtr<U>&) = delete;
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void swap(RefPtr& other)
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{
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if (this == &other)
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return;
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// NOTE: swap is not atomic!
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FlatPtr other_bits = PtrTraits::exchange(other.m_bits, PtrTraits::default_null_value);
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FlatPtr bits = PtrTraits::exchange(m_bits, other_bits);
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PtrTraits::exchange(other.m_bits, bits);
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}
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template<typename U, typename P = RefPtrTraits<U>>
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void swap(RefPtr<U, P>& other)
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{
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// NOTE: swap is not atomic!
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FlatPtr other_bits = P::exchange(other.m_bits, P::default_null_value);
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FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::template convert_from<U, P>(other_bits));
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P::exchange(other.m_bits, P::template convert_from<U, P>(bits));
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}
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ALWAYS_INLINE RefPtr& operator=(RefPtr&& other)
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{
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if (this != &other)
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assign_raw(other.leak_ref_raw());
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return *this;
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}
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template<typename U, typename P = RefPtrTraits<U>>
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ALWAYS_INLINE RefPtr& operator=(RefPtr<U, P>&& other)
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{
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assign_raw(PtrTraits::template convert_from<U, P>(other.leak_ref_raw()));
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return *this;
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}
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template<typename U>
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ALWAYS_INLINE RefPtr& operator=(NonnullRefPtr<U>&& other)
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{
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assign_raw(PtrTraits::as_bits(&other.leak_ref()));
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return *this;
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}
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ALWAYS_INLINE RefPtr& operator=(const NonnullRefPtr<T>& other)
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{
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assign_raw(PtrTraits::as_bits(other.add_ref()));
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return *this;
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}
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template<typename U>
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ALWAYS_INLINE RefPtr& operator=(const NonnullRefPtr<U>& other)
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{
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assign_raw(PtrTraits::as_bits(other.add_ref()));
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return *this;
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}
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ALWAYS_INLINE RefPtr& operator=(const RefPtr& other)
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{
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if (this != &other)
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assign_raw(other.add_ref_raw());
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return *this;
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}
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template<typename U>
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ALWAYS_INLINE RefPtr& operator=(const RefPtr<U>& other)
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{
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assign_raw(other.add_ref_raw());
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return *this;
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}
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ALWAYS_INLINE RefPtr& operator=(const T* ptr)
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{
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ref_if_not_null(const_cast<T*>(ptr));
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assign_raw(PtrTraits::as_bits(const_cast<T*>(ptr)));
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return *this;
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}
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ALWAYS_INLINE RefPtr& operator=(const T& object)
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{
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const_cast<T&>(object).ref();
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assign_raw(PtrTraits::as_bits(const_cast<T*>(&object)));
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return *this;
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}
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RefPtr& operator=(std::nullptr_t)
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{
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clear();
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return *this;
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}
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ALWAYS_INLINE bool assign_if_null(RefPtr&& other)
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{
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if (this == &other)
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return is_null();
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return PtrTraits::exchange_if_null(m_bits, other.leak_ref_raw());
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}
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template<typename U, typename P = RefPtrTraits<U>>
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ALWAYS_INLINE bool assign_if_null(RefPtr<U, P>&& other)
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{
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if (this == &other)
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return is_null();
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return PtrTraits::exchange_if_null(m_bits, PtrTraits::template convert_from<U, P>(other.leak_ref_raw()));
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}
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ALWAYS_INLINE void clear()
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{
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assign_raw(PtrTraits::default_null_value);
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}
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bool operator!() const { return PtrTraits::is_null(m_bits.load(AK::MemoryOrder::memory_order_relaxed)); }
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[[nodiscard]] T* leak_ref()
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{
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FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
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return PtrTraits::as_ptr(bits);
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}
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NonnullRefPtr<T> release_nonnull()
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{
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FlatPtr bits = PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
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VERIFY(!PtrTraits::is_null(bits));
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return NonnullRefPtr<T>(NonnullRefPtr<T>::Adopt, *PtrTraits::as_ptr(bits));
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}
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ALWAYS_INLINE T* ptr() { return as_ptr(); }
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ALWAYS_INLINE const T* ptr() const { return as_ptr(); }
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ALWAYS_INLINE T* operator->()
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{
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return as_nonnull_ptr();
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}
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ALWAYS_INLINE const T* operator->() const
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{
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return as_nonnull_ptr();
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}
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ALWAYS_INLINE T& operator*()
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{
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return *as_nonnull_ptr();
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}
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ALWAYS_INLINE const T& operator*() const
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{
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return *as_nonnull_ptr();
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}
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ALWAYS_INLINE operator const T*() const { return as_ptr(); }
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ALWAYS_INLINE operator T*() { return as_ptr(); }
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ALWAYS_INLINE operator bool() { return !is_null(); }
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bool operator==(std::nullptr_t) const { return is_null(); }
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bool operator!=(std::nullptr_t) const { return !is_null(); }
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bool operator==(const RefPtr& other) const { return as_ptr() == other.as_ptr(); }
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bool operator!=(const RefPtr& other) const { return as_ptr() != other.as_ptr(); }
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bool operator==(RefPtr& other) { return as_ptr() == other.as_ptr(); }
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bool operator!=(RefPtr& other) { return as_ptr() != other.as_ptr(); }
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bool operator==(const T* other) const { return as_ptr() == other; }
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bool operator!=(const T* other) const { return as_ptr() != other; }
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bool operator==(T* other) { return as_ptr() == other; }
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bool operator!=(T* other) { return as_ptr() != other; }
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ALWAYS_INLINE bool is_null() const { return PtrTraits::is_null(m_bits.load(AK::MemoryOrder::memory_order_relaxed)); }
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template<typename U = T, typename EnableIf<IsSame<U, T> && !IsNullPointer<typename PtrTraits::NullType>>::Type* = nullptr>
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typename PtrTraits::NullType null_value() const
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{
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// make sure we are holding a null value
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FlatPtr bits = m_bits.load(AK::MemoryOrder::memory_order_relaxed);
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VERIFY(PtrTraits::is_null(bits));
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return PtrTraits::to_null_value(bits);
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}
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template<typename U = T, typename EnableIf<IsSame<U, T> && !IsNullPointer<typename PtrTraits::NullType>>::Type* = nullptr>
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void set_null_value(typename PtrTraits::NullType value)
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{
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// make sure that new null value would be interpreted as a null value
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FlatPtr bits = PtrTraits::from_null_value(value);
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VERIFY(PtrTraits::is_null(bits));
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assign_raw(bits);
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}
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private:
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template<typename F>
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void do_while_locked(F f) const
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{
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#ifdef KERNEL
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// We don't want to be pre-empted while we have the lock bit set
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Kernel::ScopedCritical critical;
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#endif
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FlatPtr bits = PtrTraits::lock(m_bits);
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T* ptr = PtrTraits::as_ptr(bits);
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f(ptr);
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PtrTraits::unlock(m_bits, bits);
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}
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[[nodiscard]] ALWAYS_INLINE FlatPtr leak_ref_raw()
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{
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return PtrTraits::exchange(m_bits, PtrTraits::default_null_value);
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}
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[[nodiscard]] ALWAYS_INLINE FlatPtr add_ref_raw() const
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{
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#ifdef KERNEL
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// We don't want to be pre-empted while we have the lock bit set
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Kernel::ScopedCritical critical;
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#endif
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// This prevents a race condition between thread A and B:
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// 1. Thread A copies RefPtr, e.g. through assignment or copy constructor,
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// gets the pointer from source, but is pre-empted before adding
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// another reference
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// 2. Thread B calls clear, leak_ref, or release_nonnull on source, and
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// then drops the last reference, causing the object to be deleted
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// 3. Thread A finishes step #1 by attempting to add a reference to
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// the object that was already deleted in step #2
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FlatPtr bits = PtrTraits::lock(m_bits);
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if (T* ptr = PtrTraits::as_ptr(bits))
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ptr->ref();
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PtrTraits::unlock(m_bits, bits);
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return bits;
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}
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ALWAYS_INLINE void assign_raw(FlatPtr bits)
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{
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FlatPtr prev_bits = PtrTraits::exchange(m_bits, bits);
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unref_if_not_null(PtrTraits::as_ptr(prev_bits));
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}
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ALWAYS_INLINE T* as_ptr() const
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{
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return PtrTraits::as_ptr(m_bits.load(AK::MemoryOrder::memory_order_relaxed));
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}
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ALWAYS_INLINE T* as_nonnull_ptr() const
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{
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return as_nonnull_ptr(m_bits.load(AK::MemoryOrder::memory_order_relaxed));
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}
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ALWAYS_INLINE T* as_nonnull_ptr(FlatPtr bits) const
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{
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VERIFY(!PtrTraits::is_null(bits));
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return PtrTraits::as_ptr(bits);
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}
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mutable Atomic<FlatPtr> m_bits { PtrTraits::default_null_value };
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};
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template<typename T>
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struct Formatter<RefPtr<T>> : Formatter<const T*> {
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void format(FormatBuilder& builder, const RefPtr<T>& value)
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{
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Formatter<const T*>::format(builder, value.ptr());
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}
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};
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template<typename T>
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struct Traits<RefPtr<T>> : public GenericTraits<RefPtr<T>> {
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using PeekType = const T*;
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static unsigned hash(const RefPtr<T>& p) { return ptr_hash(p.ptr()); }
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static bool equals(const RefPtr<T>& a, const RefPtr<T>& b) { return a.ptr() == b.ptr(); }
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};
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template<typename T, typename U>
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inline NonnullRefPtr<T> static_ptr_cast(const NonnullRefPtr<U>& ptr)
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{
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return NonnullRefPtr<T>(static_cast<const T&>(*ptr));
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}
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template<typename T, typename U, typename PtrTraits = RefPtrTraits<T>>
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inline RefPtr<T> static_ptr_cast(const RefPtr<U>& ptr)
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{
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return RefPtr<T, PtrTraits>(static_cast<const T*>(ptr.ptr()));
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}
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template<typename T, typename PtrTraitsT, typename U, typename PtrTraitsU>
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inline void swap(RefPtr<T, PtrTraitsT>& a, RefPtr<U, PtrTraitsU>& b)
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{
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a.swap(b);
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}
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}
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using AK::RefPtr;
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using AK::static_ptr_cast;
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