DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Implementation

Mercurial (d38398e5144e)

VCS Links

Entry

FrameProperties

FramePropertyDescriptor

FramePropertyDescriptorUntyped

FramePropertyTable

FramePropertyTypeHelper

FramePropertyTypeHelper

PropertyComparator

PropertyValue

ReinterpretHelper

ReinterpretHelper

Macros

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442
/* -*- 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_ */