gecko-dev/layout/base/FramePropertyTable.h
Xidorn Quan e4d12795cc Bug 1276140 - Use memcpy rather than union to reinterpret in frame properties table. r=froydnj
MozReview-Commit-ID: Inrf22Ve9FQ

--HG--
extra : source : 525240afe663152f2b854e6d23417ef76dac9a8c
2016-05-30 09:19:25 +10:00

443 lines
14 KiB
C++

/* -*- 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 FRAMEPROPERTYTABLE_H_
#define FRAMEPROPERTYTABLE_H_
#include "mozilla/MemoryReporting.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/unused.h"
#include "nsTArray.h"
#include "nsTHashtable.h"
#include "nsHashKeys.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.
*/
MOZ_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 MOZ_CONSTEXPR const FramePropertyDescriptor<T> NewWithDestructor()
{
return { Destruct<Dtor>, nullptr };
}
template<DestructorWithFrame Dtor>
static MOZ_CONSTEXPR
const FramePropertyDescriptor<T> NewWithDestructorWithFrame()
{
return { nullptr, DestructWithFrame<Dtor> };
}
static MOZ_CONSTEXPR const FramePropertyDescriptor<T> NewWithoutDestructor()
{
return { nullptr, nullptr };
}
private:
MOZ_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 FramePropertyTable 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 FramePropertyTable {
public:
template<typename T>
using Descriptor = const FramePropertyDescriptor<T>*;
using UntypedDescriptor = const FramePropertyDescriptorUntyped*;
template<typename T>
using PropertyType = typename detail::FramePropertyTypeHelper<T>::Type;
FramePropertyTable() : mLastFrame(nullptr), mLastEntry(nullptr)
{
}
~FramePropertyTable()
{
DeleteAll();
}
/**
* Set a property value on a frame. This requires one hashtable
* lookup (using the frame as the key) and a linear search through
* the properties of that frame. Any existing value for the property
* is destroyed.
*/
template<typename T>
void Set(const nsIFrame* aFrame, Descriptor<T> aProperty,
PropertyType<T> aValue)
{
void* ptr = ReinterpretHelper<T>::ToPointer(aValue);
SetInternal(aFrame, aProperty, ptr);
}
/**
* @return true if @aProperty is set for @aFrame. This requires one hashtable
* lookup (using the frame as the key) and a linear search through the
* properties of that 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(const nsIFrame* aFrame, Descriptor<T> aProperty)
{
bool foundResult = false;
mozilla::Unused << GetInternal(aFrame, aProperty, &foundResult);
return foundResult;
}
/**
* Get a property value for a frame. This requires one hashtable
* lookup (using the frame as the key) and a linear search through
* the properties of that 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(const nsIFrame* aFrame, Descriptor<T> aProperty,
bool* aFoundResult = nullptr)
{
void* ptr = GetInternal(aFrame, aProperty, aFoundResult);
return ReinterpretHelper<T>::FromPointer(ptr);
}
/**
* Remove a property value for a frame. This requires one hashtable
* lookup (using the frame as the key) and a linear search through
* the properties of that 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(const nsIFrame* aFrame, Descriptor<T> aProperty,
bool* aFoundResult = nullptr)
{
void* ptr = RemoveInternal(aFrame, aProperty, aFoundResult);
return ReinterpretHelper<T>::FromPointer(ptr);
}
/**
* Remove and destroy a property value for a frame. This requires one
* hashtable lookup (using the frame as the key) and a linear search
* through the properties of that frame. If the frame has no such
* property, nothing happens.
*/
template<typename T>
void Delete(const nsIFrame* aFrame, Descriptor<T> aProperty)
{
DeleteInternal(aFrame, aProperty);
}
/**
* Remove and destroy all property values for a frame. This requires one
* hashtable lookup (using the frame as the key).
*/
void DeleteAllFor(const nsIFrame* aFrame);
/**
* Remove and destroy all property values for all frames.
*/
void DeleteAll();
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
protected:
void SetInternal(const nsIFrame* aFrame, UntypedDescriptor aProperty,
void* aValue);
void* GetInternal(const nsIFrame* aFrame, UntypedDescriptor aProperty,
bool* aFoundResult);
void* RemoveInternal(const nsIFrame* aFrame, UntypedDescriptor aProperty,
bool* aFoundResult);
void DeleteInternal(const nsIFrame* aFrame, UntypedDescriptor aProperty);
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. It can also be used to
* store an nsTArray of PropertyValues.
*/
struct PropertyValue {
PropertyValue() : mProperty(nullptr), mValue(nullptr) {}
PropertyValue(UntypedDescriptor aProperty, void* aValue)
: mProperty(aProperty), mValue(aValue) {}
bool IsArray() { return !mProperty && mValue; }
nsTArray<PropertyValue>* ToArray()
{
NS_ASSERTION(IsArray(), "Must be array");
return reinterpret_cast<nsTArray<PropertyValue>*>(&mValue);
}
void DestroyValueFor(const nsIFrame* aFrame) {
if (mProperty->mDestructor) {
mProperty->mDestructor(mValue);
} else if (mProperty->mDestructorWithFrame) {
mProperty->mDestructorWithFrame(aFrame, mValue);
}
}
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
size_t n = 0;
// We don't need to measure mProperty because it always points to static
// memory. As for mValue: if it's a single value we can't measure it,
// because the type is opaque; if it's an array, we measure the array
// storage, but we can't measure the individual values, again because
// their types are opaque.
if (IsArray()) {
nsTArray<PropertyValue>* array = ToArray();
n += array->ShallowSizeOfExcludingThis(aMallocSizeOf);
}
return n;
}
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;
}
};
/**
* Our hashtable entry. The key is an nsIFrame*, the value is a
* PropertyValue representing one or more property/value pairs.
*/
class Entry : public nsPtrHashKey<const nsIFrame>
{
public:
explicit Entry(KeyTypePointer aKey) : nsPtrHashKey<const nsIFrame>(aKey) {}
Entry(const Entry &toCopy) :
nsPtrHashKey<const nsIFrame>(toCopy), mProp(toCopy.mProp) {}
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
return mProp.SizeOfExcludingThis(aMallocSizeOf);
}
PropertyValue mProp;
};
static void DeleteAllForEntry(Entry* aEntry);
// Note that mLastEntry points into mEntries, so we need to be careful about
// not triggering a resize of mEntries, e.g. use RawRemoveEntry() instead of
// RemoveEntry() in some places.
nsTHashtable<Entry> mEntries;
const nsIFrame* mLastFrame;
Entry* mLastEntry;
};
/**
* This class encapsulates the properties of a frame.
*/
class FrameProperties {
public:
template<typename T> using Descriptor = FramePropertyTable::Descriptor<T>;
template<typename T> using PropertyType = FramePropertyTable::PropertyType<T>;
FrameProperties(FramePropertyTable* aTable, const nsIFrame* aFrame)
: mTable(aTable), mFrame(aFrame) {}
template<typename T>
void Set(Descriptor<T> aProperty, PropertyType<T> aValue) const
{
mTable->Set(mFrame, aProperty, aValue);
}
template<typename T>
bool Has(Descriptor<T> aProperty) const
{
return mTable->Has(mFrame, aProperty);
}
template<typename T>
PropertyType<T> Get(Descriptor<T> aProperty,
bool* aFoundResult = nullptr) const
{
return mTable->Get(mFrame, aProperty, aFoundResult);
}
template<typename T>
PropertyType<T> Remove(Descriptor<T> aProperty,
bool* aFoundResult = nullptr) const
{
return mTable->Remove(mFrame, aProperty, aFoundResult);
}
template<typename T>
void Delete(Descriptor<T> aProperty)
{
mTable->Delete(mFrame, aProperty);
}
private:
FramePropertyTable* mTable;
const nsIFrame* mFrame;
};
} // namespace mozilla
#endif /* FRAMEPROPERTYTABLE_H_ */