1 files changed, 442 insertions, 0 deletions
diff --git a/layout/base/FramePropertyTable.h b/layout/base/FramePropertyTable.h
new file mode 100644
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+++ b/layout/base/FramePropertyTable.h
@@ -0,0 +1,442 @@
+/* -*- 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.
+   */
+  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 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_ */