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https://github.com/SerenityOS/serenity
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5d180d1f99
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED) Since all of these checks are done in release builds as well, let's rename them to VERIFY to prevent confusion, as everyone is used to assertions being compiled out in release. We can introduce a new ASSERT macro that is specifically for debug checks, but I'm doing this wholesale conversion first since we've accumulated thousands of these already, and it's not immediately obvious which ones are suitable for ASSERT.
151 lines
4.5 KiB
C++
151 lines
4.5 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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#include "StdLibExtras.h"
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#ifdef KERNEL
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# include <Kernel/Arch/i386/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 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>, typename EnableIf<IsBaseOf<RefCountedBase, T>::value>::Type* = nullptr>
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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 are trying to obtain
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// a strong reference
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Kernel::ScopedCritical critical;
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#endif
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if (!(m_consumers.fetch_add(1u << 1, AK::MemoryOrder::memory_order_acquire) & 1u)) {
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T* ptr = (T*)m_ptr.load(AK::MemoryOrder::memory_order_acquire);
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if (ptr && ptr->try_ref())
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ref = adopt(*ptr);
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}
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m_consumers.fetch_sub(1u << 1, AK::MemoryOrder::memory_order_release);
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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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if (m_consumers.load(AK::MemoryOrder::memory_order_relaxed) & 1u)
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return nullptr;
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// NOTE: This may return a non-null pointer even if revocation
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// has been triggered as there is a possible race! But it's "unsafe"
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// anyway because we return a raw pointer without ensuring a
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// reference...
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return (T*)m_ptr.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 !unsafe_ptr<void>();
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}
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void revoke()
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{
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auto current_consumers = m_consumers.fetch_or(1u, AK::MemoryOrder::memory_order_relaxed);
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VERIFY(!(current_consumers & 1u));
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// We flagged revokation, now wait until everyone trying to obtain
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// a strong reference is done
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while (current_consumers > 0) {
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#ifdef KERNEL
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Kernel::Processor::wait_check();
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#else
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// TODO: yield?
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#endif
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current_consumers = m_consumers.load(AK::MemoryOrder::memory_order_acquire) & ~1u;
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}
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// No one is trying to use it (anymore)
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m_ptr.store(nullptr, AK::MemoryOrder::memory_order_release);
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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_ptr(&weakable)
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{
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}
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mutable Atomic<void*> m_ptr;
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mutable Atomic<unsigned> m_consumers; // LSB indicates revokation in progress
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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() = default;
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~Weakable()
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{
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m_being_destroyed.store(true, AK::MemoryOrder::memory_order_release);
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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 (auto link = move(m_link))
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link->revoke();
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}
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private:
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mutable RefPtr<WeakLink> m_link;
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Atomic<bool> m_being_destroyed { false };
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};
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}
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using AK::Weakable;
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