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https://github.com/SerenityOS/serenity
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75f61fe3d9
This makes most operations thread safe, especially so that they can safely be used in the Kernel. This includes obtaining a strong reference from a weak reference, which now requires an explicit call to WeakPtr::strong_ref(). Another major change is that Weakable::make_weak_ref() may require the explicit target type. Previously we used reinterpret_cast in WeakPtr, assuming that it can be properly converted. But WeakPtr does not necessarily have the knowledge to be able to do this. Instead, we now ask the class itself to deliver a WeakPtr to the type that we want. Also, WeakLink is no longer specific to a target type. The reason for this is that we want to be able to safely convert e.g. WeakPtr<T> to WeakPtr<U>, and before this we just reinterpret_cast the internal WeakLink<T> to WeakLink<U>, which is a bold assumption that it would actually produce the correct code. Instead, WeakLink now operates on just a raw pointer and we only make those constructors/operators available if we can verify that it can be safely cast. In order to guarantee thread safety, we now use the least significant bit in the pointer for locking purposes. This also means that only properly aligned pointers can be used.
133 lines
3.4 KiB
C++
133 lines
3.4 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include "Assertions.h"
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#include "Atomic.h"
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#include "RefCounted.h"
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#include "RefPtr.h"
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#ifndef WEAKABLE_DEBUG
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# define WEAKABLE_DEBUG
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#endif
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namespace AK {
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template<typename T>
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class Weakable;
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template<typename T>
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class WeakPtr;
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class WeakLink : public RefCounted<WeakLink> {
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template<typename T>
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friend class Weakable;
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template<typename T>
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friend class WeakPtr;
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public:
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template<typename T, typename PtrTraits = RefPtrTraits<T>>
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RefPtr<T, PtrTraits> strong_ref() const
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{
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RefPtr<T, PtrTraits> ref;
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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 = RefPtrTraits<void>::lock(m_bits);
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T* ptr = static_cast<T*>(RefPtrTraits<void>::as_ptr(bits));
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if (ptr)
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ref = *ptr;
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RefPtrTraits<void>::unlock(m_bits, bits);
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}
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return ref;
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}
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template<typename T>
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T* unsafe_ptr() const
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{
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return static_cast<T*>(RefPtrTraits<void>::as_ptr(m_bits.load(AK::MemoryOrder::memory_order_acquire)));
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}
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bool is_null() const
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{
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return RefPtrTraits<void>::is_null(m_bits.load(AK::MemoryOrder::memory_order_relaxed));
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}
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void revoke()
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{
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RefPtrTraits<void>::exchange(m_bits, RefPtrTraits<void>::default_null_value);
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}
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private:
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template<typename T>
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explicit WeakLink(T& weakable)
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: m_bits(RefPtrTraits<void>::as_bits(&weakable))
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{
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}
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mutable Atomic<FlatPtr> m_bits;
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};
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template<typename T>
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class Weakable {
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private:
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class Link;
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public:
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template<typename U = T>
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WeakPtr<U> make_weak_ptr() const;
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protected:
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Weakable() { }
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~Weakable()
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{
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#ifdef WEAKABLE_DEBUG
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m_being_destroyed = true;
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#endif
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revoke_weak_ptrs();
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}
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void revoke_weak_ptrs()
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{
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if (m_link)
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m_link->revoke();
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}
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private:
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mutable RefPtr<WeakLink> m_link;
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#ifdef WEAKABLE_DEBUG
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bool m_being_destroyed { false };
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#endif
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};
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}
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using AK::Weakable;
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