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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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
#ifndef FRAMEPROPERTIES_H_
#define FRAMEPROPERTIES_H_
#include "mozilla/DebugOnly.h"
#include "mozilla/MemoryReporting.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 FrameProperties methods.
*/
template <typename T>
struct FramePropertyDescriptor : public FramePropertyDescriptorUntyped {
typedef void Destructor(T* aPropertyValue);
typedef void DestructorWithFrame(const nsIFrame* aFrame, 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 directly into our
// internal value slot (i.e. types that can fit in 64 bits). 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;
};
} // namespace detail
/**
* 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.
*/
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() = default;
~FrameProperties() {
MOZ_ASSERT(mProperties.Length() == 0, "forgot to delete properties");
}
/**
* Return true if we have no properties, otherwise return false.
*/
bool IsEmpty() const { return mProperties.IsEmpty(); }
/**
* 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) {
uint64_t v = ReinterpretHelper<T>::ToInternalValue(aValue);
SetInternal(aProperty, v, aFrame);
}
/**
* Add a property value; the descriptor MUST NOT already be present.
*/
template <typename T>
void Add(Descriptor<T> aProperty, PropertyType<T> aValue) {
MOZ_ASSERT(!Has(aProperty), "duplicate frame property");
uint64_t v = ReinterpretHelper<T>::ToInternalValue(aValue);
AddInternal(aProperty, v);
}
/**
* @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 Take() 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.Contains(aProperty, PropertyComparator());
}
/**
* Get a property value. This requires 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 {
uint64_t v = GetInternal(aProperty, aFoundResult);
return ReinterpretHelper<T>::FromInternalValue(v);
}
/**
* Remove a property value, and return it without destroying it.
*
* This requires 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 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> Take(Descriptor<T> aProperty, bool* aFoundResult = nullptr) {
uint64_t v = TakeInternal(aProperty, aFoundResult);
return ReinterpretHelper<T>::FromInternalValue(v);
}
/**
* 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 Remove(Descriptor<T> aProperty, const nsIFrame* aFrame) {
RemoveInternal(aProperty, aFrame);
}
/**
* Call @aFunction for each property or until @aFunction returns false.
*/
template <class F>
void ForEach(F aFunction) const {
#ifdef DEBUG
size_t len = mProperties.Length();
#endif
for (const auto& prop : mProperties) {
bool shouldContinue = aFunction(prop.mProperty, prop.mValue);
MOZ_ASSERT(len == mProperties.Length(),
"frame property list was modified by ForEach callback!");
if (!shouldContinue) {
return;
}
}
}
/**
* Remove and destroy all property values for the frame.
*/
void RemoveAll(const nsIFrame* aFrame) {
nsTArray<PropertyValue> toDelete = std::move(mProperties);
for (auto& prop : toDelete) {
prop.DestroyValueFor(aFrame);
}
MOZ_ASSERT(mProperties.IsEmpty(), "a property dtor added new properties");
}
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:
// 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, uint64_t aValue,
const nsIFrame* aFrame);
inline void AddInternal(UntypedDescriptor aProperty, uint64_t aValue);
inline uint64_t GetInternal(UntypedDescriptor aProperty,
bool* aFoundResult) const;
inline uint64_t TakeInternal(UntypedDescriptor aProperty, bool* aFoundResult);
inline void RemoveInternal(UntypedDescriptor aProperty,
const nsIFrame* aFrame);
template <typename T>
struct ReinterpretHelper {
static_assert(sizeof(PropertyType<T>) <= sizeof(uint64_t),
"size of the value must never be larger than 64 bits");
static uint64_t ToInternalValue(PropertyType<T> aValue) {
uint64_t v = 0;
memcpy(&v, &aValue, sizeof(aValue));
return v;
}
static PropertyType<T> FromInternalValue(uint64_t aInternalValue) {
PropertyType<T> value;
memcpy(&value, &aInternalValue, sizeof(value));
return value;
}
};
/**
* Stores a property descriptor/value pair.
*/
struct PropertyValue {
PropertyValue() : mProperty(nullptr), mValue(0) {}
PropertyValue(UntypedDescriptor aProperty, uint64_t aValue)
: mProperty(aProperty), mValue(aValue) {}
// NOTE: This function converts our internal 64-bit-integer representation
// to a pointer-type representation. This is lossy on 32-bit systems, but it
// should be fine, as long as we *only* do this in cases where we're sure
// that the stored property-value is in fact a pointer. And we should have
// that assurance, since only pointer-typed frame properties are expected to
// have a destructor
void DestroyValueFor(const nsIFrame* aFrame) {
if (mProperty->mDestructor) {
mProperty->mDestructor(
ReinterpretHelper<void*>::FromInternalValue(mValue));
} else if (mProperty->mDestructorWithFrame) {
mProperty->mDestructorWithFrame(
aFrame, ReinterpretHelper<void*>::FromInternalValue(mValue));
}
}
UntypedDescriptor mProperty;
uint64_t 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;
};
inline uint64_t FrameProperties::GetInternal(UntypedDescriptor aProperty,
bool* aFoundResult) const {
MOZ_ASSERT(aProperty, "Null property?");
return mProperties.ApplyIf(
aProperty, 0, PropertyComparator(),
[&aFoundResult](const PropertyValue& aPV) -> uint64_t {
if (aFoundResult) {
*aFoundResult = true;
}
return aPV.mValue;
},
[&aFoundResult]() -> uint64_t {
if (aFoundResult) {
*aFoundResult = false;
}
return 0;
});
}
inline void FrameProperties::SetInternal(UntypedDescriptor aProperty,
uint64_t aValue,
const nsIFrame* aFrame) {
MOZ_ASSERT(NS_IsMainThread());
MOZ_ASSERT(aProperty, "Null property?");
mProperties.ApplyIf(
aProperty, 0, PropertyComparator(),
[&](PropertyValue& aPV) {
aPV.DestroyValueFor(aFrame);
aPV.mValue = aValue;
},
[&]() { mProperties.AppendElement(PropertyValue(aProperty, aValue)); });
}
inline void FrameProperties::AddInternal(UntypedDescriptor aProperty,
uint64_t aValue) {
MOZ_ASSERT(NS_IsMainThread());
MOZ_ASSERT(aProperty, "Null property?");
mProperties.AppendElement(PropertyValue(aProperty, aValue));
}
inline uint64_t FrameProperties::TakeInternal(UntypedDescriptor aProperty,
bool* aFoundResult) {
MOZ_ASSERT(NS_IsMainThread());
MOZ_ASSERT(aProperty, "Null property?");
auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
if (index == nsTArray<PropertyValue>::NoIndex) {
if (aFoundResult) {
*aFoundResult = false;
}
return 0;
}
if (aFoundResult) {
*aFoundResult = true;
}
uint64_t result = mProperties.Elements()[index].mValue;
mProperties.RemoveElementAtUnsafe(index);
return result;
}
inline void FrameProperties::RemoveInternal(UntypedDescriptor aProperty,
const nsIFrame* aFrame) {
MOZ_ASSERT(NS_IsMainThread());
MOZ_ASSERT(aProperty, "Null property?");
auto index = mProperties.IndexOf(aProperty, 0, PropertyComparator());
if (index != nsTArray<PropertyValue>::NoIndex) {
mProperties.Elements()[index].DestroyValueFor(aFrame);
mProperties.RemoveElementAtUnsafe(index);
}
}
} // namespace mozilla
#endif /* FRAMEPROPERTIES_H_ */