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+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef FRAMEPROPERTIES_H_
+#define FRAMEPROPERTIES_H_
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/Unused.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+
+class nsIFrame;
+
+namespace mozilla {
+
+struct FramePropertyDescriptorUntyped
+{
+ /**
+ * mDestructor will be called if it's non-null.
+ */
+ typedef void UntypedDestructor(void* aPropertyValue);
+ UntypedDestructor* mDestructor;
+ /**
+ * mDestructorWithFrame will be called if it's non-null and mDestructor
+ * is null. WARNING: The frame passed to mDestructorWithFrame may
+ * be a dangling frame pointer, if this is being called during
+ * presshell teardown. Do not use it except to compare against
+ * other frame pointers. No frame will have been allocated with
+ * the same address yet.
+ */
+ typedef void UntypedDestructorWithFrame(const nsIFrame* aFrame,
+ void* aPropertyValue);
+ UntypedDestructorWithFrame* mDestructorWithFrame;
+ /**
+ * mDestructor and mDestructorWithFrame may both be null, in which case
+ * no value destruction is a no-op.
+ */
+
+protected:
+ /**
+ * At most one destructor should be passed in. In general, you should
+ * just use the static function FramePropertyDescriptor::New* below
+ * instead of using this constructor directly.
+ */
+ constexpr FramePropertyDescriptorUntyped(
+ UntypedDestructor* aDtor, UntypedDestructorWithFrame* aDtorWithFrame)
+ : mDestructor(aDtor)
+ , mDestructorWithFrame(aDtorWithFrame)
+ {}
+};
+
+/**
+ * A pointer to a FramePropertyDescriptor serves as a unique property ID.
+ * The FramePropertyDescriptor stores metadata about the property.
+ * Currently the only metadata is a destructor function. The destructor
+ * function is called on property values when they are overwritten or
+ * deleted.
+ *
+ * To use this class, declare a global (i.e., file, class or function-scope
+ * static member) FramePropertyDescriptor and pass its address as
+ * aProperty in the FramePropertyTable methods.
+ */
+template<typename T>
+struct FramePropertyDescriptor : public FramePropertyDescriptorUntyped
+{
+ typedef void Destructor(T* aPropertyValue);
+ typedef void DestructorWithFrame(const nsIFrame* aaFrame,
+ T* aPropertyValue);
+
+ template<Destructor Dtor>
+ static constexpr const FramePropertyDescriptor<T> NewWithDestructor()
+ {
+ return { Destruct<Dtor>, nullptr };
+ }
+
+ template<DestructorWithFrame Dtor>
+ static constexpr
+ const FramePropertyDescriptor<T> NewWithDestructorWithFrame()
+ {
+ return { nullptr, DestructWithFrame<Dtor> };
+ }
+
+ static constexpr const FramePropertyDescriptor<T> NewWithoutDestructor()
+ {
+ return { nullptr, nullptr };
+ }
+
+private:
+ constexpr FramePropertyDescriptor(
+ UntypedDestructor* aDtor, UntypedDestructorWithFrame* aDtorWithFrame)
+ : FramePropertyDescriptorUntyped(aDtor, aDtorWithFrame)
+ {}
+
+ template<Destructor Dtor>
+ static void Destruct(void* aPropertyValue)
+ {
+ Dtor(static_cast<T*>(aPropertyValue));
+ }
+
+ template<DestructorWithFrame Dtor>
+ static void DestructWithFrame(const nsIFrame* aFrame, void* aPropertyValue)
+ {
+ Dtor(aFrame, static_cast<T*>(aPropertyValue));
+ }
+};
+
+// SmallValueHolder<T> is a placeholder intended to be used as template
+// argument of FramePropertyDescriptor for types which can fit into the
+// size of a pointer directly. This class should never be defined, so
+// that we won't use it for unexpected purpose by mistake.
+template<typename T>
+class SmallValueHolder;
+
+namespace detail {
+
+template<typename T>
+struct FramePropertyTypeHelper
+{
+ typedef T* Type;
+};
+template<typename T>
+struct FramePropertyTypeHelper<SmallValueHolder<T>>
+{
+ typedef T Type;
+};
+
+}
+
+/**
+ * The FrameProperties class is optimized for storing 0 or 1 properties on
+ * a given frame. Storing very large numbers of properties on a single
+ * frame will not be efficient.
+ *
+ * Property values are passed as void* but do not actually have to be
+ * valid pointers. You can use NS_INT32_TO_PTR/NS_PTR_TO_INT32 to
+ * store int32_t values. Null/zero values can be stored and retrieved.
+ * Of course, the destructor function (if any) must handle such values
+ * correctly.
+ */
+class FrameProperties
+{
+public:
+ template<typename T>
+ using Descriptor = const FramePropertyDescriptor<T>*;
+ using UntypedDescriptor = const FramePropertyDescriptorUntyped*;
+
+ template<typename T>
+ using PropertyType = typename detail::FramePropertyTypeHelper<T>::Type;
+
+ explicit FrameProperties()
+ {
+ }
+
+ ~FrameProperties()
+ {
+ MOZ_ASSERT(mProperties.Length() == 0, "forgot to delete properties");
+ }
+
+ /**
+ * Set a property value. This requires a linear search through
+ * the properties of the frame. Any existing value for the property
+ * is destroyed.
+ */
+ template<typename T>
+ void Set(Descriptor<T> aProperty, PropertyType<T> aValue,
+ const nsIFrame* aFrame)
+ {
+ void* ptr = ReinterpretHelper<T>::ToPointer(aValue);
+ SetInternal(aProperty, ptr, aFrame);
+ }
+
+ /**
+ * @return true if @aProperty is set. This requires a linear search through the
+ * properties of the frame.
+ *
+ * In most cases, this shouldn't be used outside of assertions, because if
+ * you're doing a lookup anyway it would be far more efficient to call Get()
+ * or Remove() and check the aFoundResult outparam to find out whether the
+ * property is set. Legitimate non-assertion uses include:
+ *
+ * - Checking if a frame property is set in cases where that's all we want
+ * to know (i.e., we don't intend to read the actual value or remove the
+ * property).
+ *
+ * - Calling Has() before Set() in cases where we don't want to overwrite
+ * an existing value for the frame property.
+ */
+ template<typename T>
+ bool Has(Descriptor<T> aProperty) const
+ {
+ return mProperties.IndexOf(aProperty, 0, PropertyComparator()) != nsTArray<PropertyValue>::NoIndex;
+ }
+
+ /**
+ * Get a property value. This requires a linear search through
+ * lookup (using the frame as the key) and a linear search through
+ * the properties of the frame. If the frame has no such property,
+ * returns zero-filled result, which means null for pointers and
+ * zero for integers and floating point types.
+ * @param aFoundResult if non-null, receives a value 'true' iff
+ * the frame has a value for the property. This lets callers
+ * disambiguate a null result, which can mean 'no such property' or
+ * 'property value is null'.
+ */
+ template<typename T>
+ PropertyType<T> Get(Descriptor<T> aProperty,
+ bool* aFoundResult = nullptr) const
+ {
+ void* ptr = GetInternal(aProperty, aFoundResult);
+ return ReinterpretHelper<T>::FromPointer(ptr);
+ }
+ /**
+ * Remove a property value. This requires a linear search through
+ * the properties of the frame. The old property value is returned
+ * (and not destroyed). If the frame has no such property,
+ * returns zero-filled result, which means null for pointers and
+ * zero for integers and floating point types.
+ * @param aFoundResult if non-null, receives a value 'true' iff
+ * the frame had a value for the property. This lets callers
+ * disambiguate a null result, which can mean 'no such property' or
+ * 'property value is null'.
+ */
+ template<typename T>
+ PropertyType<T> Remove(Descriptor<T> aProperty,
+ bool* aFoundResult = nullptr)
+ {
+ void* ptr = RemoveInternal(aProperty, aFoundResult);
+ return ReinterpretHelper<T>::FromPointer(ptr);
+ }
+ /**
+ * Remove and destroy a property value. This requires a linear search
+ * through the properties of the frame. If the frame has no such
+ * property, nothing happens.
+ */
+ template<typename T>
+ void Delete(Descriptor<T> aProperty, const nsIFrame* aFrame)
+ {
+ DeleteInternal(aProperty, aFrame);
+ }
+ /**
+ * Remove and destroy all property values for the frame.
+ */
+ void DeleteAll(const nsIFrame* aFrame) {
+ mozilla::DebugOnly<size_t> len = mProperties.Length();
+ for (auto& prop : mProperties) {
+ prop.DestroyValueFor(aFrame);
+ MOZ_ASSERT(mProperties.Length() == len);
+ }
+ mProperties.Clear();
+ }
+
+ size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+ // We currently report only the shallow size of the mProperties array.
+ // As for the PropertyValue entries: we don't need to measure the mProperty
+ // field of because it always points to static memory, and we can't measure
+ // mValue because the type is opaque.
+ // XXX Can we do better, e.g. with a method on the descriptor?
+ return mProperties.ShallowSizeOfExcludingThis(aMallocSizeOf);
+ }
+
+private:
+ friend class ::nsIFrame;
+
+ // Prevent copying of FrameProperties; we should always return/pass around
+ // references to it, not copies!
+ FrameProperties(const FrameProperties&) = delete;
+ FrameProperties& operator=(const FrameProperties&) = delete;
+
+ inline void
+ SetInternal(UntypedDescriptor aProperty, void* aValue,
+ const nsIFrame* aFrame);
+
+ inline void*
+ GetInternal(UntypedDescriptor aProperty, bool* aFoundResult) const;
+
+ inline void*
+ RemoveInternal(UntypedDescriptor aProperty, bool* aFoundResult);
+
+ inline void
+ DeleteInternal(UntypedDescriptor aProperty, const nsIFrame* aFrame);
+
+ template<typename T>
+ struct ReinterpretHelper
+ {
+ static_assert(sizeof(PropertyType<T>) <= sizeof(void*),
+ "size of the value must never be larger than a pointer");
+
+ static void* ToPointer(PropertyType<T> aValue)
+ {
+ void* ptr = nullptr;
+ memcpy(&ptr, &aValue, sizeof(aValue));
+ return ptr;
+ }
+
+ static PropertyType<T> FromPointer(void* aPtr)
+ {
+ PropertyType<T> value;
+ memcpy(&value, &aPtr, sizeof(value));
+ return value;
+ }
+ };
+
+ template<typename T>
+ struct ReinterpretHelper<T*>
+ {
+ static void* ToPointer(T* aValue)
+ {
+ return static_cast<void*>(aValue);
+ }
+
+ static T* FromPointer(void* aPtr)
+ {
+ return static_cast<T*>(aPtr);
+ }
+ };
+
+ /**
+ * Stores a property descriptor/value pair.
+ */
+ struct PropertyValue {
+ PropertyValue() : mProperty(nullptr), mValue(nullptr) {}
+ PropertyValue(UntypedDescriptor aProperty, void* aValue)
+ : mProperty(aProperty), mValue(aValue) {}
+
+ void DestroyValueFor(const nsIFrame* aFrame) {
+ if (mProperty->mDestructor) {
+ mProperty->mDestructor(mValue);
+ } else if (mProperty->mDestructorWithFrame) {
+ mProperty->mDestructorWithFrame(aFrame, mValue);
+ }
+ }
+
+ UntypedDescriptor mProperty;
+ void* mValue;
+ };
+
+ /**
+ * Used with an array of PropertyValues to allow lookups that compare
+ * only on the FramePropertyDescriptor.
+ */
+ class PropertyComparator {
+ public:
+ bool Equals(const PropertyValue& a, const PropertyValue& b) const {
+ return a.mProperty == b.mProperty;
+ }
+ bool Equals(UntypedDescriptor a, const PropertyValue& b) const {
+ return a == b.mProperty;
+ }
+ bool Equals(const PropertyValue& a, UntypedDescriptor b) const {
+ return a.mProperty == b;
+ }
+ };
+
+ nsTArray<PropertyValue> mProperties;
+};
+
+/**
+ * This class encapsulates the properties of a frame.
+ */
+inline void*
+FrameProperties::GetInternal(UntypedDescriptor aProperty,
+ bool* aFoundResult) const
+{
+ MOZ_ASSERT(aProperty, "Null property?");
+
+ auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
+ if (index == nsTArray<PropertyValue>::NoIndex) {
+ if (aFoundResult) {
+ *aFoundResult = false;
+ }
+ return nullptr;
+ }
+
+ if (aFoundResult) {
+ *aFoundResult = true;
+ }
+
+return mProperties.ElementAt(index).mValue;
+}
+
+inline void
+FrameProperties::SetInternal(UntypedDescriptor aProperty, void* aValue,
+ const nsIFrame* aFrame)
+{
+ MOZ_ASSERT(aProperty, "Null property?");
+
+ auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
+ if (index != nsTArray<PropertyValue>::NoIndex) {
+ PropertyValue* pv = &mProperties.ElementAt(index);
+ pv->DestroyValueFor(aFrame);
+ pv->mValue = aValue;
+ return;
+ }
+
+ mProperties.AppendElement(PropertyValue(aProperty, aValue));
+}
+
+inline void*
+FrameProperties::RemoveInternal(UntypedDescriptor aProperty, bool* aFoundResult)
+{
+ MOZ_ASSERT(aProperty, "Null property?");
+
+ auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
+ if (index == nsTArray<PropertyValue>::NoIndex) {
+ if (aFoundResult) {
+ *aFoundResult = false;
+ }
+ return nullptr;
+ }
+
+if (aFoundResult) {
+ *aFoundResult = true;
+}
+
+void* result = mProperties.ElementAt(index).mValue;
+mProperties.RemoveElementAt(index);
+
+return result;
+}
+
+inline void
+FrameProperties::DeleteInternal(UntypedDescriptor aProperty,
+ const nsIFrame* aFrame)
+{
+ MOZ_ASSERT(aProperty, "Null property?");
+
+ auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
+ if (index != nsTArray<PropertyValue>::NoIndex) {
+ mProperties.ElementAt(index).DestroyValueFor(aFrame);
+ mProperties.RemoveElementAt(index);
+ }
+}
+
+} // namespace mozilla
+
+#endif /* FRAMEPROPERTIES_H_ */