image/SurfaceCache.h

   1 /* -*- Mode: C++; tab-width: 2; 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 /**
   7  * SurfaceCache is a service for caching temporary surfaces and decoded image
   8  * data in imagelib.
   9  */
  10
  11 #ifndef mozilla_image_SurfaceCache_h
  12 #define mozilla_image_SurfaceCache_h
  13
  14 #include "mozilla/Maybe.h"  // for Maybe
  15 #include "mozilla/NotNull.h"
  16 #include "mozilla/MemoryReporting.h"  // for MallocSizeOf
  17 #include "mozilla/HashFunctions.h"    // for HashGeneric and AddToHash
  18 #include "gfx2DGlue.h"
  19 #include "gfxPoint.h"           // for gfxSize
  20 #include "nsCOMPtr.h"           // for already_AddRefed
  21 #include "mozilla/gfx/Point.h"  // for mozilla::gfx::IntSize
  22 #include "mozilla/gfx/2D.h"     // for SourceSurface
  23 #include "PlaybackType.h"
  24 #include "SurfaceFlags.h"
  25 #include "SVGImageContext.h"  // for SVGImageContext
  26
  27 namespace mozilla {
  28 namespace image {
  29
  30 class Image;
  31 class ISurfaceProvider;
  32 class LookupResult;
  33 class SurfaceCacheImpl;
  34 struct SurfaceMemoryCounter;
  35
  36 /*
  37  * ImageKey contains the information we need to look up all SurfaceCache entries
  38  * for a particular image.
  39  */
  40 typedef Image* ImageKey;
  41
  42 /*
  43  * SurfaceKey contains the information we need to look up a specific
  44  * SurfaceCache entry. Together with an ImageKey, this uniquely identifies the
  45  * surface.
  46  *
  47  * Callers should construct a SurfaceKey using the appropriate helper function
  48  * for their image type - either RasterSurfaceKey or VectorSurfaceKey.
  49  */
  50 class SurfaceKey {
  51   typedef gfx::IntSize IntSize;
  52
  53  public:
  54   bool operator==(const SurfaceKey& aOther) const {
  55     return aOther.mSize == mSize && aOther.mSVGContext == mSVGContext &&
  56            aOther.mPlayback == mPlayback && aOther.mFlags == mFlags;
  57   }
  58
  59   PLDHashNumber Hash() const {
  60     PLDHashNumber hash = HashGeneric(mSize.width, mSize.height);
  61     hash = AddToHash(hash, mSVGContext.map(HashSIC).valueOr(0));
  62     hash = AddToHash(hash, uint8_t(mPlayback), uint32_t(mFlags));
  63     return hash;
  64   }
  65
  66   SurfaceKey CloneWithSize(const IntSize& aSize) const {
  67     return SurfaceKey(aSize, mSVGContext, mPlayback, mFlags);
  68   }
  69
  70   const IntSize& Size() const { return mSize; }
  71   const Maybe<SVGImageContext>& SVGContext() const { return mSVGContext; }
  72   PlaybackType Playback() const { return mPlayback; }
  73   SurfaceFlags Flags() const { return mFlags; }
  74
  75  private:
  76   SurfaceKey(const IntSize& aSize, const Maybe<SVGImageContext>& aSVGContext,
  77              PlaybackType aPlayback, SurfaceFlags aFlags)
  78       : mSize(aSize),
  79         mSVGContext(aSVGContext),
  80         mPlayback(aPlayback),
  81         mFlags(aFlags) {}
  82
  83   static PLDHashNumber HashSIC(const SVGImageContext& aSIC) {
  84     return aSIC.Hash();
  85   }
  86
  87   friend SurfaceKey RasterSurfaceKey(const IntSize&, SurfaceFlags,
  88                                      PlaybackType);
  89   friend SurfaceKey VectorSurfaceKey(const IntSize&,
  90                                      const Maybe<SVGImageContext>&);
  91
  92   IntSize mSize;
  93   Maybe<SVGImageContext> mSVGContext;
  94   PlaybackType mPlayback;
  95   SurfaceFlags mFlags;
  96 };
  97
  98 inline SurfaceKey RasterSurfaceKey(const gfx::IntSize& aSize,
  99                                    SurfaceFlags aFlags,
 100                                    PlaybackType aPlayback) {
 101   return SurfaceKey(aSize, Nothing(), aPlayback, aFlags);
 102 }
 103
 104 inline SurfaceKey VectorSurfaceKey(const gfx::IntSize& aSize,
 105                                    const Maybe<SVGImageContext>& aSVGContext) {
 106   // We don't care about aFlags for VectorImage because none of the flags we
 107   // have right now influence VectorImage's rendering. If we add a new flag that
 108   // *does* affect how a VectorImage renders, we'll have to change this.
 109   // Similarly, we don't accept a PlaybackType parameter because we don't
 110   // currently cache frames of animated SVG images.
 111   return SurfaceKey(aSize, aSVGContext, PlaybackType::eStatic,
 112                     DefaultSurfaceFlags());
 113 }
 114
 115 /**
 116  * AvailabilityState is used to track whether an ISurfaceProvider has a surface
 117  * available or is just a placeholder.
 118  *
 119  * To ensure that availability changes are atomic (and especially that internal
 120  * SurfaceCache code doesn't have to deal with asynchronous availability
 121  * changes), an ISurfaceProvider which starts as a placeholder can only reveal
 122  * the fact that it now has a surface available via a call to
 123  * SurfaceCache::SurfaceAvailable().
 124  *
 125  * It also tracks whether or not there are "explicit" users of this surface
 126  * which will not accept substitutes. This is used by SurfaceCache when pruning
 127  * unnecessary surfaces from the cache.
 128  */
 129 class AvailabilityState {
 130  public:
 131   static AvailabilityState StartAvailable() { return AvailabilityState(true); }
 132   static AvailabilityState StartAsPlaceholder() {
 133     return AvailabilityState(false);
 134   }
 135
 136   bool IsAvailable() const { return mIsAvailable; }
 137   bool IsPlaceholder() const { return !mIsAvailable; }
 138   bool CannotSubstitute() const { return mCannotSubstitute; }
 139
 140   void SetCannotSubstitute() { mCannotSubstitute = true; }
 141
 142  private:
 143   friend class SurfaceCacheImpl;
 144
 145   explicit AvailabilityState(bool aIsAvailable)
 146       : mIsAvailable(aIsAvailable), mCannotSubstitute(false) {}
 147
 148   void SetAvailable() { mIsAvailable = true; }
 149
 150   bool mIsAvailable : 1;
 151   bool mCannotSubstitute : 1;
 152 };
 153
 154 enum class InsertOutcome : uint8_t {
 155   SUCCESS,                 // Success (but see Insert documentation).
 156   FAILURE,                 // Couldn't insert (e.g., for capacity reasons).
 157   FAILURE_ALREADY_PRESENT  // A surface with the same key is already present.
 158 };
 159
 160 /**
 161  * SurfaceCache is an ImageLib-global service that allows caching of decoded
 162  * image surfaces, temporary surfaces (e.g. for caching rotated or clipped
 163  * versions of images), or dynamically generated surfaces (e.g. for animations).
 164  * SurfaceCache entries normally expire from the cache automatically if they go
 165  * too long without being accessed.
 166  *
 167  * Because SurfaceCache must support both normal surfaces and dynamically
 168  * generated surfaces, it does not actually hold surfaces directly. Instead, it
 169  * holds ISurfaceProvider objects which can provide access to a surface when
 170  * requested; SurfaceCache doesn't care about the details of how this is
 171  * accomplished.
 172  *
 173  * Sometime it's useful to temporarily prevent entries from expiring from the
 174  * cache. This is most often because losing the data could harm the user
 175  * experience (for example, we often don't want to allow surfaces that are
 176  * currently visible to expire) or because it's not possible to rematerialize
 177  * the surface. SurfaceCache supports this through the use of image locking; see
 178  * the comments for Insert() and LockImage() for more details.
 179  *
 180  * Any image which stores surfaces in the SurfaceCache *must* ensure that it
 181  * calls RemoveImage() before it is destroyed. See the comments for
 182  * RemoveImage() for more details.
 183  */
 184 struct SurfaceCache {
 185   typedef gfx::IntSize IntSize;
 186
 187   /**
 188    * Initialize static data. Called during imagelib module initialization.
 189    */
 190   static void Initialize();
 191
 192   /**
 193    * Release static data. Called during imagelib module shutdown.
 194    */
 195   static void Shutdown();
 196
 197   /**
 198    * Looks up the requested cache entry and returns a drawable reference to its
 199    * associated surface.
 200    *
 201    * If the image associated with the cache entry is locked, then the entry will
 202    * be locked before it is returned.
 203    *
 204    * If a matching ISurfaceProvider was found in the cache, but SurfaceCache
 205    * couldn't obtain a surface from it (e.g. because it had stored its surface
 206    * in a volatile buffer which was discarded by the OS) then it is
 207    * automatically removed from the cache and an empty LookupResult is returned.
 208    * Note that this will never happen to ISurfaceProviders associated with a
 209    * locked image; SurfaceCache tells such ISurfaceProviders to keep a strong
 210    * references to their data internally.
 211    *
 212    * @param aImageKey       Key data identifying which image the cache entry
 213    *                        belongs to.
 214    * @param aSurfaceKey     Key data which uniquely identifies the requested
 215    *                        cache entry.
 216    * @return                a LookupResult which will contain a DrawableSurface
 217    *                        if the cache entry was found.
 218    */
 219   static LookupResult Lookup(const ImageKey aImageKey,
 220                              const SurfaceKey& aSurfaceKey, bool aMarkUsed);
 221
 222   /**
 223    * Looks up the best matching cache entry and returns a drawable reference to
 224    * its associated surface.
 225    *
 226    * The result may vary from the requested cache entry only in terms of size.
 227    *
 228    * @param aImageKey       Key data identifying which image the cache entry
 229    *                        belongs to.
 230    * @param aSurfaceKey     Key data which uniquely identifies the requested
 231    *                        cache entry.
 232    * @return                a LookupResult which will contain a DrawableSurface
 233    *                        if a cache entry similar to the one the caller
 234    *                        requested could be found. Callers can use
 235    *                        LookupResult::IsExactMatch() to check whether the
 236    *                        returned surface exactly matches @aSurfaceKey.
 237    */
 238   static LookupResult LookupBestMatch(const ImageKey aImageKey,
 239                                       const SurfaceKey& aSurfaceKey,
 240                                       bool aMarkUsed);
 241
 242   /**
 243    * Insert an ISurfaceProvider into the cache. If an entry with the same
 244    * ImageKey and SurfaceKey is already in the cache, Insert returns
 245    * FAILURE_ALREADY_PRESENT. If a matching placeholder is already present, it
 246    * is replaced.
 247    *
 248    * Cache entries will never expire as long as they remain locked, but if they
 249    * become unlocked, they can expire either because the SurfaceCache runs out
 250    * of capacity or because they've gone too long without being used.  When it
 251    * is first inserted, a cache entry is locked if its associated image is
 252    * locked.  When that image is later unlocked, the cache entry becomes
 253    * unlocked too. To become locked again at that point, two things must happen:
 254    * the image must become locked again (via LockImage()), and the cache entry
 255    * must be touched again (via one of the Lookup() functions).
 256    *
 257    * All of this means that a very particular procedure has to be followed for
 258    * cache entries which cannot be rematerialized. First, they must be inserted
 259    * *after* the image is locked with LockImage(); if you use the other order,
 260    * the cache entry might expire before LockImage() gets called or before the
 261    * entry is touched again by Lookup(). Second, the image they are associated
 262    * with must never be unlocked.
 263    *
 264    * If a cache entry cannot be rematerialized, it may be important to know
 265    * whether it was inserted into the cache successfully. Insert() returns
 266    * FAILURE if it failed to insert the cache entry, which could happen because
 267    * of capacity reasons, or because it was already freed by the OS. If the
 268    * cache entry isn't associated with a locked image, checking for SUCCESS or
 269    * FAILURE is useless: the entry might expire immediately after being
 270    * inserted, even though Insert() returned SUCCESS. Thus, many callers do not
 271    * need to check the result of Insert() at all.
 272    *
 273    * @param aProvider    The new cache entry to insert into the cache.
 274    * @return SUCCESS if the cache entry was inserted successfully. (But see
 275    *           above for more information about when you should check this.)
 276    *         FAILURE if the cache entry could not be inserted, e.g. for capacity
 277    *           reasons. (But see above for more information about when you
 278    *           should check this.)
 279    *         FAILURE_ALREADY_PRESENT if an entry with the same ImageKey and
 280    *           SurfaceKey already exists in the cache.
 281    */
 282   static InsertOutcome Insert(NotNull<ISurfaceProvider*> aProvider);
 283
 284   /**
 285    * Mark the cache entry @aProvider as having an available surface. This turns
 286    * a placeholder cache entry into a normal cache entry. The cache entry
 287    * becomes locked if the associated image is locked; otherwise, it starts in
 288    * the unlocked state.
 289    *
 290    * If the cache entry containing @aProvider has already been evicted from the
 291    * surface cache, this function has no effect.
 292    *
 293    * It's illegal to call this function if @aProvider is not a placeholder; by
 294    * definition, non-placeholder ISurfaceProviders should have a surface
 295    * available already.
 296    *
 297    * @param aProvider       The cache entry that now has a surface available.
 298    */
 299   static void SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider);
 300
 301   /**
 302    * Checks if a surface of a given size could possibly be stored in the cache.
 303    * If CanHold() returns false, Insert() will always fail to insert the
 304    * surface, but the inverse is not true: Insert() may take more information
 305    * into account than just image size when deciding whether to cache the
 306    * surface, so Insert() may still fail even if CanHold() returns true.
 307    *
 308    * Use CanHold() to avoid the need to create a temporary surface when we know
 309    * for sure the cache can't hold it.
 310    *
 311    * @param aSize  The dimensions of a surface in pixels.
 312    * @param aBytesPerPixel  How many bytes each pixel of the surface requires.
 313    *                        Defaults to 4, which is appropriate for RGBA or RGBX
 314    *                        images.
 315    *
 316    * @return false if the surface cache can't hold a surface of that size.
 317    */
 318   static bool CanHold(const IntSize& aSize, uint32_t aBytesPerPixel = 4);
 319   static bool CanHold(size_t aSize);
 320
 321   /**
 322    * Locks an image. Any of the image's cache entries which are either inserted
 323    * or accessed while the image is locked will not expire.
 324    *
 325    * Locking an image does not automatically lock that image's existing cache
 326    * entries. A call to LockImage() guarantees that entries which are inserted
 327    * afterward will not expire before the next call to UnlockImage() or
 328    * UnlockSurfaces() for that image. Cache entries that are accessed via
 329    * Lookup() or LookupBestMatch() after a LockImage() call will also not expire
 330    * until the next UnlockImage() or UnlockSurfaces() call for that image. Any
 331    * other cache entries owned by the image may expire at any time.
 332    *
 333    * All of an image's cache entries are removed by RemoveImage(), whether the
 334    * image is locked or not.
 335    *
 336    * It's safe to call LockImage() on an image that's already locked; this has
 337    * no effect.
 338    *
 339    * You must always unlock any image you lock. You may do this explicitly by
 340    * calling UnlockImage(), or implicitly by calling RemoveImage(). Since you're
 341    * required to call RemoveImage() when you destroy an image, this doesn't
 342    * impose any additional requirements, but it's preferable to call
 343    * UnlockImage() earlier if it's possible.
 344    *
 345    * @param aImageKey    The image to lock.
 346    */
 347   static void LockImage(const ImageKey aImageKey);
 348
 349   /**
 350    * Unlocks an image, allowing any of its cache entries to expire at any time.
 351    *
 352    * It's OK to call UnlockImage() on an image that's already unlocked; this has
 353    * no effect.
 354    *
 355    * @param aImageKey    The image to unlock.
 356    */
 357   static void UnlockImage(const ImageKey aImageKey);
 358
 359   /**
 360    * Unlocks the existing cache entries of an image, allowing them to expire at
 361    * any time.
 362    *
 363    * This does not unlock the image itself, so accessing the cache entries via
 364    * Lookup() or LookupBestMatch() will lock them again, and prevent them from
 365    * expiring.
 366    *
 367    * This is intended to be used in situations where it's no longer clear that
 368    * all of the cache entries owned by an image are needed. Calling
 369    * UnlockSurfaces() and then taking some action that will cause Lookup() to
 370    * touch any cache entries that are still useful will permit the remaining
 371    * entries to expire from the cache.
 372    *
 373    * If the image is unlocked, this has no effect.
 374    *
 375    * @param aImageKey    The image which should have its existing cache entries
 376    *                     unlocked.
 377    */
 378   static void UnlockEntries(const ImageKey aImageKey);
 379
 380   /**
 381    * Removes all cache entries (including placeholders) associated with the
 382    * given image from the cache.  If the image is locked, it is automatically
 383    * unlocked.
 384    *
 385    * This MUST be called, at a minimum, when an Image which could be storing
 386    * entries in the surface cache is destroyed. If another image were allocated
 387    * at the same address it could result in subtle, difficult-to-reproduce bugs.
 388    *
 389    * @param aImageKey  The image which should be removed from the cache.
 390    */
 391   static void RemoveImage(const ImageKey aImageKey);
 392
 393   /**
 394    * Attempts to remove cache entries (including placeholders) associated with
 395    * the given image from the cache, assuming there is an equivalent entry that
 396    * it is able substitute that entry with. Note that this only applies if the
 397    * image is in factor of 2 mode. If it is not, this operation does nothing.
 398    *
 399    * @param aImageKey  The image whose cache which should be pruned.
 400    */
 401   static void PruneImage(const ImageKey aImageKey);
 402
 403   /**
 404    * Evicts all evictable entries from the cache.
 405    *
 406    * All entries are evictable except for entries associated with locked images.
 407    * Non-evictable entries can only be removed by RemoveImage().
 408    */
 409   static void DiscardAll();
 410
 411   /**
 412    * Collects an accounting of the surfaces contained in the SurfaceCache for
 413    * the given image, along with their size and various other metadata.
 414    *
 415    * This is intended for use with memory reporting.
 416    *
 417    * @param aImageKey     The image to report memory usage for.
 418    * @param aCounters     An array into which the report for each surface will
 419    *                      be written.
 420    * @param aMallocSizeOf A fallback malloc memory reporting function.
 421    */
 422   static void CollectSizeOfSurfaces(const ImageKey aImageKey,
 423                                     nsTArray<SurfaceMemoryCounter>& aCounters,
 424                                     MallocSizeOf aMallocSizeOf);
 425
 426   /**
 427    * @return maximum capacity of the SurfaceCache in bytes. This is only exposed
 428    * for use by tests; normal code should use CanHold() instead.
 429    */
 430   static size_t MaximumCapacity();
 431
 432   /**
 433    * @return true if the given size is valid.
 434    */
 435   static bool IsLegalSize(const IntSize& aSize);
 436
 437   /**
 438    * @return clamped size for the given vector image size to rasterize at.
 439    */
 440   static IntSize ClampVectorSize(const IntSize& aSize);
 441
 442   /**
 443    * @return clamped size for the given image and size to rasterize at.
 444    */
 445   static IntSize ClampSize(const ImageKey aImageKey, const IntSize& aSize);
 446
 447  private:
 448   virtual ~SurfaceCache() = 0;  // Forbid instantiation.
 449 };
 450
 451 }  // namespace image
 452 }  // namespace mozilla
 453
 454 #endif  // mozilla_image_SurfaceCache_h