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https://github.com/RGBCube/serenity
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AK: Make RefPtr, NonnullRefPtr, WeakPtr thread safe
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.
This commit is contained in:
Tom
Andreas Kling
parent
3c1ef744f6
commit
75f61fe3d9
50 changed files with 819 additions and 322 deletions
199
AK/WeakPtr.h
199
AK/WeakPtr.h
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@ -31,82 +31,209 @@
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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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class WeakPtr {
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friend class Weakable<T>;
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template<typename U>
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friend class Weakable;
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public:
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WeakPtr() { }
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WeakPtr(std::nullptr_t) { }
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template<typename U>
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WeakPtr(WeakPtr<U>&& other)
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: m_link(reinterpret_cast<WeakLink<T>*>(other.take_link().ptr()))
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(const WeakPtr<U>& other)
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: m_link(other.m_link)
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{
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}
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template<typename U>
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(WeakPtr<U>&& other)
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: m_link(other.take_link())
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{
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(WeakPtr<U>&& other)
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{
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m_link = reinterpret_cast<WeakLink<T>*>(other.take_link().ptr());
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m_link = other.take_link();
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return *this;
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}
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operator bool() const { return ptr(); }
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(const WeakPtr<U>& other)
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{
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if ((const void*)this != (const void*)&other)
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m_link = other.m_link;
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return *this;
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}
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T* ptr() { return m_link ? m_link->ptr() : nullptr; }
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const T* ptr() const { return m_link ? m_link->ptr() : nullptr; }
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WeakPtr& 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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T* operator->() { return ptr(); }
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const T* operator->() const { return ptr(); }
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T& operator*() { return *ptr(); }
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const T& operator*() const { return *ptr(); }
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operator const T*() const { return ptr(); }
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operator T*() { return ptr(); }
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bool is_null() const { return !m_link || !m_link->ptr(); }
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void clear() { m_link = nullptr; }
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RefPtr<WeakLink<T>> take_link() { return move(m_link); }
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bool operator==(const OwnPtr<T>& other) const { return ptr() == other.ptr(); }
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private:
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WeakPtr(RefPtr<WeakLink<T>> link)
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: m_link(move(link))
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(const U& object)
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: m_link(object.template make_weak_ptr<U>().take_link())
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{
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}
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RefPtr<WeakLink<T>> m_link;
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(const U* object)
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{
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if (object)
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m_link = object->template make_weak_ptr<U>().take_link();
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(const RefPtr<U>& object)
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{
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object.do_while_locked([&](U* obj) {
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if (obj)
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obj->template make_weak_ptr<U>().take_link();
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});
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr(const NonnullRefPtr<U>& object)
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{
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object.do_while_locked([&](U* obj) {
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if (obj)
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obj->template make_weak_ptr<U>().take_link();
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});
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(const U& object)
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{
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m_link = object.template make_weak_ptr<U>().take_link();
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return *this;
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(const U* object)
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{
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if (object)
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m_link = object->template make_weak_ptr<U>().take_link();
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else
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m_link = nullptr;
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return *this;
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(const RefPtr<U>& object)
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{
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object.do_while_locked([&](U* obj) {
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if (obj)
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m_link = obj->template make_weak_ptr<U>().take_link();
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else
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m_link = nullptr;
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});
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return *this;
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}
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template<typename U, typename EnableIf<IsBaseOf<T, U>::value>::Type* = nullptr>
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WeakPtr& operator=(const NonnullRefPtr<U>& object)
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{
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object.do_while_locked([&](U* obj) {
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if (obj)
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m_link = obj->template make_weak_ptr<U>().take_link();
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else
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m_link = nullptr;
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});
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return *this;
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}
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RefPtr<T> strong_ref() const
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{
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// This only works with RefCounted objects, but it is the only
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// safe way to get a strong reference from a WeakPtr. Any code
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// that uses objects not derived from RefCounted will have to
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// use unsafe_ptr(), but as the name suggests, it is not safe...
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RefPtr<T> ref;
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// Using do_while_locked protects against a race with clear()!
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m_link.do_while_locked([&](WeakLink* link) {
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if (link)
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ref = link->template strong_ref<T>();
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});
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return ref;
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}
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#ifndef KERNEL
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// A lot of user mode code is single-threaded. But for kernel mode code
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// this is generally not true as everything is multi-threaded. So make
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// these shortcuts and aliases only available to non-kernel code.
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T* ptr() const { return unsafe_ptr(); }
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T* operator->() { return unsafe_ptr(); }
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const T* operator->() const { return unsafe_ptr(); }
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operator const T*() const { return unsafe_ptr(); }
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operator T*() { return unsafe_ptr(); }
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#endif
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T* unsafe_ptr() const
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{
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T* ptr = nullptr;
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m_link.do_while_locked([&](WeakLink* link) {
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if (link)
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ptr = link->unsafe_ptr<T>();
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});
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return ptr;
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}
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operator bool() const { return m_link ? !m_link->is_null() : false; }
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bool is_null() const { return !m_link || m_link->is_null(); }
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void clear() { m_link = nullptr; }
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RefPtr<WeakLink> take_link() { return move(m_link); }
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private:
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WeakPtr(const RefPtr<WeakLink>& link)
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: m_link(link)
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{
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}
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RefPtr<WeakLink> m_link;
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};
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template<typename T>
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inline WeakPtr<T> Weakable<T>::make_weak_ptr()
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template<typename U>
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inline WeakPtr<U> Weakable<T>::make_weak_ptr() const
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{
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#ifdef DEBUG
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ASSERT(!m_being_destroyed);
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#endif
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if (!m_link)
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m_link = adopt(*new WeakLink<T>(static_cast<T&>(*this)));
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return WeakPtr<T>(m_link);
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if (!m_link) {
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// There is a small chance that we create a new WeakLink and throw
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// it away because another thread beat us to it. But the window is
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// pretty small and the overhead isn't terrible.
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m_link.assign_if_null(adopt(*new WeakLink(const_cast<T&>(static_cast<const T&>(*this)))));
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}
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return WeakPtr<U>(m_link);
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}
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template<typename T>
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inline const LogStream& operator<<(const LogStream& stream, const WeakPtr<T>& value)
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{
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#ifdef KERNEL
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auto ref = value.strong_ref();
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return stream << ref.ptr();
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#else
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return stream << value.ptr();
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#endif
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}
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template<typename T>
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struct Formatter<WeakPtr<T>> : Formatter<const T*> {
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void format(TypeErasedFormatParams& params, FormatBuilder& builder, const WeakPtr<T>& value)
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{
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#ifdef KERNEL
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auto ref = value.strong_ref();
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Formatter<const T*>::format(params, builder, ref.ptr());
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#else
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Formatter<const T*>::format(params, builder, value.ptr());
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#endif
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}
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};
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