FramePropertyTable.h
/* -*- 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 "nsTArray.h"
#include "nsTHashtable.h"
#include "nsHashKeys.h"
class nsIFrame;
namespace mozilla {
struct FramePropertyDescriptor;
typedef void (*FramePropertyDestructor)(void* aPropertyValue);
typedef void (*FramePropertyDestructorWithFrame)(nsIFrame* aFrame,
void* aPropertyValue);
/**
* 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.
*/
struct FramePropertyDescriptor {
/**
* mDestructor will be called if it's non-null.
*/
FramePropertyDestructor 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.
*/
FramePropertyDestructorWithFrame mDestructorWithFrame;
/**
* mDestructor and mDestructorWithFrame may both be null, in which case
* no value destruction is a no-op.
*/
};
/**
* 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:
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.
*/
void Set(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
void* aValue);
/**
* 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 null.
* @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'.
*/
void* Get(const nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
bool* aFoundResult = nullptr);
/**
* 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 null.
* @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'.
*/
void* Remove(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
bool* aFoundResult = nullptr);
/**
* 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.
*/
void Delete(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty);
/**
* Remove and destroy all property values for a frame. This requires one
* hashtable lookup (using the frame as the key).
*/
void DeleteAllFor(nsIFrame* aFrame);
/**
* Remove and destroy all property values for all frames.
*/
void DeleteAll();
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
protected:
/**
* 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(const FramePropertyDescriptor* 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(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->SizeOfExcludingThis(aMallocSizeOf);
}
return n;
}
const FramePropertyDescriptor* 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(const FramePropertyDescriptor* a, const PropertyValue& b) const {
return a == b.mProperty;
}
bool Equals(const PropertyValue& a, const FramePropertyDescriptor* 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<nsIFrame>
{
public:
Entry(KeyTypePointer aKey) : nsPtrHashKey<nsIFrame>(aKey) {}
Entry(const Entry &toCopy) :
nsPtrHashKey<nsIFrame>(toCopy), mProp(toCopy.mProp) {}
PropertyValue mProp;
};
static void DeleteAllForEntry(Entry* aEntry);
static PLDHashOperator DeleteEnumerator(Entry* aEntry, void* aArg);
static size_t SizeOfPropertyTableEntryExcludingThis(Entry* aEntry,
mozilla::MallocSizeOf aMallocSizeOf, void *);
nsTHashtable<Entry> mEntries;
nsIFrame* mLastFrame;
Entry* mLastEntry;
};
/**
* This class encapsulates the properties of a frame.
*/
class FrameProperties {
public:
FrameProperties(FramePropertyTable* aTable, nsIFrame* aFrame)
: mTable(aTable), mFrame(aFrame) {}
FrameProperties(FramePropertyTable* aTable, const nsIFrame* aFrame)
: mTable(aTable), mFrame(const_cast<nsIFrame*>(aFrame)) {}
void Set(const FramePropertyDescriptor* aProperty, void* aValue) const
{
mTable->Set(mFrame, aProperty, aValue);
}
void* Get(const FramePropertyDescriptor* aProperty,
bool* aFoundResult = nullptr) const
{
return mTable->Get(mFrame, aProperty, aFoundResult);
}
void* Remove(const FramePropertyDescriptor* aProperty,
bool* aFoundResult = nullptr) const
{
return mTable->Remove(mFrame, aProperty, aFoundResult);
}
void Delete(const FramePropertyDescriptor* aProperty)
{
mTable->Delete(mFrame, aProperty);
}
private:
FramePropertyTable* mTable;
nsIFrame* mFrame;
};
}
#endif /* FRAMEPROPERTYTABLE_H_ */
