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