layout/base/FramePropertyTable.h

   1 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef FRAMEPROPERTYTABLE_H_
   7 #define FRAMEPROPERTYTABLE_H_
   8
   9 #include "mozilla/MemoryReporting.h"
  10 #include "nsTArray.h"
  11 #include "nsTHashtable.h"
  12 #include "nsHashKeys.h"
  13
  14 class nsIFrame;
  15
  16 namespace mozilla {
  17
  18 struct FramePropertyDescriptor;
  19
  20 typedef void (*FramePropertyDestructor)(void* aPropertyValue);
  21 typedef void (*FramePropertyDestructorWithFrame)(nsIFrame* aFrame,
  22                                                  void* aPropertyValue);
  23
  24 /**
  25  * A pointer to a FramePropertyDescriptor serves as a unique property ID.
  26  * The FramePropertyDescriptor stores metadata about the property.
  27  * Currently the only metadata is a destructor function. The destructor
  28  * function is called on property values when they are overwritten or
  29  * deleted.
  30  *
  31  * To use this class, declare a global (i.e., file, class or function-scope
  32  * static member) FramePropertyDescriptor and pass its address as
  33  * aProperty in the FramePropertyTable methods.
  34  */
  35 struct FramePropertyDescriptor {
  36   /**
  37    * mDestructor will be called if it's non-null.
  38    */
  39   FramePropertyDestructor          mDestructor;
  40   /**
  41    * mDestructorWithFrame will be called if it's non-null and mDestructor
  42    * is null. WARNING: The frame passed to mDestructorWithFrame may
  43    * be a dangling frame pointer, if this is being called during
  44    * presshell teardown. Do not use it except to compare against
  45    * other frame pointers. No frame will have been allocated with
  46    * the same address yet.
  47    */
  48   FramePropertyDestructorWithFrame mDestructorWithFrame;
  49   /**
  50    * mDestructor and mDestructorWithFrame may both be null, in which case
  51    * no value destruction is a no-op.
  52    */
  53 };
  54
  55 /**
  56  * The FramePropertyTable is optimized for storing 0 or 1 properties on
  57  * a given frame. Storing very large numbers of properties on a single
  58  * frame will not be efficient.
  59  *
  60  * Property values are passed as void* but do not actually have to be
  61  * valid pointers. You can use NS_INT32_TO_PTR/NS_PTR_TO_INT32 to
  62  * store int32_t values. Null/zero values can be stored and retrieved.
  63  * Of course, the destructor function (if any) must handle such values
  64  * correctly.
  65  */
  66 class FramePropertyTable {
  67 public:
  68   FramePropertyTable() : mLastFrame(nullptr), mLastEntry(nullptr)
  69   {
  70   }
  71   ~FramePropertyTable()
  72   {
  73     DeleteAll();
  74   }
  75
  76   /**
  77    * Set a property value on a frame. This requires one hashtable
  78    * lookup (using the frame as the key) and a linear search through
  79    * the properties of that frame. Any existing value for the property
  80    * is destroyed.
  81    */
  82   void Set(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
  83            void* aValue);
  84   /**
  85    * Get a property value for a frame. This requires one hashtable
  86    * lookup (using the frame as the key) and a linear search through
  87    * the properties of that frame. If the frame has no such property,
  88    * returns null.
  89    * @param aFoundResult if non-null, receives a value 'true' iff
  90    * the frame has a value for the property. This lets callers
  91    * disambiguate a null result, which can mean 'no such property' or
  92    * 'property value is null'.
  93    */
  94   void* Get(const nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
  95             bool* aFoundResult = nullptr);
  96   /**
  97    * Remove a property value for a frame. This requires one hashtable
  98    * lookup (using the frame as the key) and a linear search through
  99    * the properties of that frame. The old property value is returned
 100    * (and not destroyed). If the frame has no such property,
 101    * returns null.
 102    * @param aFoundResult if non-null, receives a value 'true' iff
 103    * the frame had a value for the property. This lets callers
 104    * disambiguate a null result, which can mean 'no such property' or
 105    * 'property value is null'.
 106    */
 107   void* Remove(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
 108                bool* aFoundResult = nullptr);
 109   /**
 110    * Remove and destroy a property value for a frame. This requires one
 111    * hashtable lookup (using the frame as the key) and a linear search
 112    * through the properties of that frame. If the frame has no such
 113    * property, nothing happens.
 114    */
 115   void Delete(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty);
 116   /**
 117    * Remove and destroy all property values for a frame. This requires one
 118    * hashtable lookup (using the frame as the key).
 119    */
 120   void DeleteAllFor(nsIFrame* aFrame);
 121   /**
 122    * Remove and destroy all property values for all frames.
 123    */
 124   void DeleteAll();
 125
 126   size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
 127
 128 protected:
 129   /**
 130    * Stores a property descriptor/value pair. It can also be used to
 131    * store an nsTArray of PropertyValues.
 132    */
 133   struct PropertyValue {
 134     PropertyValue() : mProperty(nullptr), mValue(nullptr) {}
 135     PropertyValue(const FramePropertyDescriptor* aProperty, void* aValue)
 136       : mProperty(aProperty), mValue(aValue) {}
 137
 138     bool IsArray() { return !mProperty && mValue; }
 139     nsTArray<PropertyValue>* ToArray()
 140     {
 141       NS_ASSERTION(IsArray(), "Must be array");
 142       return reinterpret_cast<nsTArray<PropertyValue>*>(&mValue);
 143     }
 144
 145     void DestroyValueFor(nsIFrame* aFrame) {
 146       if (mProperty->mDestructor) {
 147         mProperty->mDestructor(mValue);
 148       } else if (mProperty->mDestructorWithFrame) {
 149         mProperty->mDestructorWithFrame(aFrame, mValue);
 150       }
 151     }
 152
 153     size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
 154       size_t n = 0;
 155       // We don't need to measure mProperty because it always points to static
 156       // memory.  As for mValue:  if it's a single value we can't measure it,
 157       // because the type is opaque;  if it's an array, we measure the array
 158       // storage, but we can't measure the individual values, again because
 159       // their types are opaque.
 160       if (IsArray()) {
 161         nsTArray<PropertyValue>* array = ToArray();
 162         n += array->SizeOfExcludingThis(aMallocSizeOf);
 163       }
 164       return n;
 165     }
 166
 167     const FramePropertyDescriptor* mProperty;
 168     void* mValue;
 169   };
 170
 171   /**
 172    * Used with an array of PropertyValues to allow lookups that compare
 173    * only on the FramePropertyDescriptor.
 174    */
 175   class PropertyComparator {
 176   public:
 177     bool Equals(const PropertyValue& a, const PropertyValue& b) const {
 178       return a.mProperty == b.mProperty;
 179     }
 180     bool Equals(const FramePropertyDescriptor* a, const PropertyValue& b) const {
 181       return a == b.mProperty;
 182     }
 183     bool Equals(const PropertyValue& a, const FramePropertyDescriptor* b) const {
 184       return a.mProperty == b;
 185     }
 186   };
 187
 188   /**
 189    * Our hashtable entry. The key is an nsIFrame*, the value is a
 190    * PropertyValue representing one or more property/value pairs.
 191    */
 192   class Entry : public nsPtrHashKey<nsIFrame>
 193   {
 194   public:
 195     explicit Entry(KeyTypePointer aKey) : nsPtrHashKey<nsIFrame>(aKey) {}
 196     Entry(const Entry &toCopy) :
 197       nsPtrHashKey<nsIFrame>(toCopy), mProp(toCopy.mProp) {}
 198
 199     size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
 200       return mProp.SizeOfExcludingThis(aMallocSizeOf);
 201     }
 202
 203     PropertyValue mProp;
 204   };
 205
 206   static void DeleteAllForEntry(Entry* aEntry);
 207   static PLDHashOperator DeleteEnumerator(Entry* aEntry, void* aArg);
 208
 209   nsTHashtable<Entry> mEntries;
 210   nsIFrame* mLastFrame;
 211   Entry* mLastEntry;
 212 };
 213
 214 /**
 215  * This class encapsulates the properties of a frame.
 216  */
 217 class FrameProperties {
 218 public:
 219   FrameProperties(FramePropertyTable* aTable, nsIFrame* aFrame)
 220     : mTable(aTable), mFrame(aFrame) {}
 221   FrameProperties(FramePropertyTable* aTable, const nsIFrame* aFrame)
 222     : mTable(aTable), mFrame(const_cast<nsIFrame*>(aFrame)) {}
 223
 224   void Set(const FramePropertyDescriptor* aProperty, void* aValue) const
 225   {
 226     mTable->Set(mFrame, aProperty, aValue);
 227   }
 228   void* Get(const FramePropertyDescriptor* aProperty,
 229             bool* aFoundResult = nullptr) const
 230   {
 231     return mTable->Get(mFrame, aProperty, aFoundResult);
 232   }
 233   void* Remove(const FramePropertyDescriptor* aProperty,
 234                bool* aFoundResult = nullptr) const
 235   {
 236     return mTable->Remove(mFrame, aProperty, aFoundResult);
 237   }
 238   void Delete(const FramePropertyDescriptor* aProperty)
 239   {
 240     mTable->Delete(mFrame, aProperty);
 241   }
 242
 243 private:
 244   FramePropertyTable* mTable;
 245   nsIFrame* mFrame;
 246 };
 247
 248 }
 249
 250 #endif /* FRAMEPROPERTYTABLE_H_ */