image/SurfaceCache.cpp

   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 in imagelib.
   8  */
   9
  10 #include "SurfaceCache.h"
  11
  12 #include <algorithm>
  13 #include <utility>
  14
  15 #include "ISurfaceProvider.h"
  16 #include "Image.h"
  17 #include "LookupResult.h"
  18 #include "ShutdownTracker.h"
  19 #include "gfx2DGlue.h"
  20 #include "gfxPlatform.h"
  21 #include "imgFrame.h"
  22 #include "mozilla/AppShutdown.h"
  23 #include "mozilla/Assertions.h"
  24 #include "mozilla/Attributes.h"
  25 #include "mozilla/CheckedInt.h"
  26 #include "mozilla/DebugOnly.h"
  27 #include "mozilla/Likely.h"
  28 #include "mozilla/RefPtr.h"
  29 #include "mozilla/StaticMutex.h"
  30 #include "mozilla/StaticPrefs_image.h"
  31 #include "mozilla/StaticPtr.h"
  32
  33 #include "nsExpirationTracker.h"
  34 #include "nsHashKeys.h"
  35 #include "nsIMemoryReporter.h"
  36 #include "nsRefPtrHashtable.h"
  37 #include "nsSize.h"
  38 #include "nsTArray.h"
  39 #include "Orientation.h"
  40 #include "prsystem.h"
  41
  42 using std::max;
  43 using std::min;
  44
  45 namespace mozilla {
  46
  47 using namespace gfx;
  48
  49 namespace image {
  50
  51 MOZ_DEFINE_MALLOC_SIZE_OF(SurfaceCacheMallocSizeOf)
  52
  53 class CachedSurface;
  54 class SurfaceCacheImpl;
  55
  56 ///////////////////////////////////////////////////////////////////////////////
  57 // Static Data
  58 ///////////////////////////////////////////////////////////////////////////////
  59
  60 // The single surface cache instance.
  61 static StaticRefPtr<SurfaceCacheImpl> sInstance;
  62
  63 // The mutex protecting the surface cache.
  64 static StaticMutex sInstanceMutex MOZ_UNANNOTATED;
  65
  66 ///////////////////////////////////////////////////////////////////////////////
  67 // SurfaceCache Implementation
  68 ///////////////////////////////////////////////////////////////////////////////
  69
  70 /**
  71  * Cost models the cost of storing a surface in the cache. Right now, this is
  72  * simply an estimate of the size of the surface in bytes, but in the future it
  73  * may be worth taking into account the cost of rematerializing the surface as
  74  * well.
  75  */
  76 typedef size_t Cost;
  77
  78 static Cost ComputeCost(const IntSize& aSize, uint32_t aBytesPerPixel) {
  79   MOZ_ASSERT(aBytesPerPixel == 1 || aBytesPerPixel == 4);
  80   return aSize.width * aSize.height * aBytesPerPixel;
  81 }
  82
  83 /**
  84  * Since we want to be able to make eviction decisions based on cost, we need to
  85  * be able to look up the CachedSurface which has a certain cost as well as the
  86  * cost associated with a certain CachedSurface. To make this possible, in data
  87  * structures we actually store a CostEntry, which contains a weak pointer to
  88  * its associated surface.
  89  *
  90  * To make usage of the weak pointer safe, SurfaceCacheImpl always calls
  91  * StartTracking after a surface is stored in the cache and StopTracking before
  92  * it is removed.
  93  */
  94 class CostEntry {
  95  public:
  96   CostEntry(NotNull<CachedSurface*> aSurface, Cost aCost)
  97       : mSurface(aSurface), mCost(aCost) {}
  98
  99   NotNull<CachedSurface*> Surface() const { return mSurface; }
 100   Cost GetCost() const { return mCost; }
 101
 102   bool operator==(const CostEntry& aOther) const {
 103     return mSurface == aOther.mSurface && mCost == aOther.mCost;
 104   }
 105
 106   bool operator<(const CostEntry& aOther) const {
 107     return mCost < aOther.mCost ||
 108            (mCost == aOther.mCost && mSurface < aOther.mSurface);
 109   }
 110
 111  private:
 112   NotNull<CachedSurface*> mSurface;
 113   Cost mCost;
 114 };
 115
 116 /**
 117  * A CachedSurface associates a surface with a key that uniquely identifies that
 118  * surface.
 119  */
 120 class CachedSurface {
 121   ~CachedSurface() {}
 122
 123  public:
 124   MOZ_DECLARE_REFCOUNTED_TYPENAME(CachedSurface)
 125   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CachedSurface)
 126
 127   explicit CachedSurface(NotNull<ISurfaceProvider*> aProvider)
 128       : mProvider(aProvider), mIsLocked(false) {}
 129
 130   DrawableSurface GetDrawableSurface() const {
 131     if (MOZ_UNLIKELY(IsPlaceholder())) {
 132       MOZ_ASSERT_UNREACHABLE("Called GetDrawableSurface() on a placeholder");
 133       return DrawableSurface();
 134     }
 135
 136     return mProvider->Surface();
 137   }
 138
 139   DrawableSurface GetDrawableSurfaceEvenIfPlaceholder() const {
 140     return mProvider->Surface();
 141   }
 142
 143   void SetLocked(bool aLocked) {
 144     if (IsPlaceholder()) {
 145       return;  // Can't lock a placeholder.
 146     }
 147
 148     // Update both our state and our provider's state. Some surface providers
 149     // are permanently locked; maintaining our own locking state enables us to
 150     // respect SetLocked() even when it's meaningless from the provider's
 151     // perspective.
 152     mIsLocked = aLocked;
 153     mProvider->SetLocked(aLocked);
 154   }
 155
 156   bool IsLocked() const {
 157     return !IsPlaceholder() && mIsLocked && mProvider->IsLocked();
 158   }
 159
 160   void SetCannotSubstitute() {
 161     mProvider->Availability().SetCannotSubstitute();
 162   }
 163   bool CannotSubstitute() const {
 164     return mProvider->Availability().CannotSubstitute();
 165   }
 166
 167   bool IsPlaceholder() const {
 168     return mProvider->Availability().IsPlaceholder();
 169   }
 170   bool IsDecoded() const { return !IsPlaceholder() && mProvider->IsFinished(); }
 171
 172   ImageKey GetImageKey() const { return mProvider->GetImageKey(); }
 173   const SurfaceKey& GetSurfaceKey() const { return mProvider->GetSurfaceKey(); }
 174   nsExpirationState* GetExpirationState() { return &mExpirationState; }
 175
 176   CostEntry GetCostEntry() {
 177     return image::CostEntry(WrapNotNull(this), mProvider->LogicalSizeInBytes());
 178   }
 179
 180   size_t ShallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
 181     return aMallocSizeOf(this) + aMallocSizeOf(mProvider.get());
 182   }
 183
 184   void InvalidateRecording() { mProvider->InvalidateRecording(); }
 185
 186   // A helper type used by SurfaceCacheImpl::CollectSizeOfSurfaces.
 187   struct MOZ_STACK_CLASS SurfaceMemoryReport {
 188     SurfaceMemoryReport(nsTArray<SurfaceMemoryCounter>& aCounters,
 189                         MallocSizeOf aMallocSizeOf)
 190         : mCounters(aCounters), mMallocSizeOf(aMallocSizeOf) {}
 191
 192     void Add(NotNull<CachedSurface*> aCachedSurface, bool aIsFactor2) {
 193       if (aCachedSurface->IsPlaceholder()) {
 194         return;
 195       }
 196
 197       // Record the memory used by the ISurfaceProvider. This may not have a
 198       // straightforward relationship to the size of the surface that
 199       // DrawableRef() returns if the surface is generated dynamically. (i.e.,
 200       // for surfaces with PlaybackType::eAnimated.)
 201       aCachedSurface->mProvider->AddSizeOfExcludingThis(
 202           mMallocSizeOf, [&](ISurfaceProvider::AddSizeOfCbData& aMetadata) {
 203             SurfaceMemoryCounter counter(aCachedSurface->GetSurfaceKey(),
 204                                          aCachedSurface->IsLocked(),
 205                                          aCachedSurface->CannotSubstitute(),
 206                                          aIsFactor2, aMetadata.mFinished);
 207
 208             counter.Values().SetDecodedHeap(aMetadata.mHeapBytes);
 209             counter.Values().SetDecodedNonHeap(aMetadata.mNonHeapBytes);
 210             counter.Values().SetDecodedUnknown(aMetadata.mUnknownBytes);
 211             counter.Values().SetExternalHandles(aMetadata.mExternalHandles);
 212             counter.Values().SetFrameIndex(aMetadata.mIndex);
 213             counter.Values().SetExternalId(aMetadata.mExternalId);
 214             counter.Values().SetSurfaceTypes(aMetadata.mTypes);
 215
 216             mCounters.AppendElement(counter);
 217           });
 218     }
 219
 220    private:
 221     nsTArray<SurfaceMemoryCounter>& mCounters;
 222     MallocSizeOf mMallocSizeOf;
 223   };
 224
 225  private:
 226   nsExpirationState mExpirationState;
 227   NotNull<RefPtr<ISurfaceProvider>> mProvider;
 228   bool mIsLocked;
 229 };
 230
 231 static int64_t AreaOfIntSize(const IntSize& aSize) {
 232   return static_cast<int64_t>(aSize.width) * static_cast<int64_t>(aSize.height);
 233 }
 234
 235 /**
 236  * An ImageSurfaceCache is a per-image surface cache. For correctness we must be
 237  * able to remove all surfaces associated with an image when the image is
 238  * destroyed or invalidated. Since this will happen frequently, it makes sense
 239  * to make it cheap by storing the surfaces for each image separately.
 240  *
 241  * ImageSurfaceCache also keeps track of whether its associated image is locked
 242  * or unlocked.
 243  *
 244  * The cache may also enter "factor of 2" mode which occurs when the number of
 245  * surfaces in the cache exceeds the "image.cache.factor2.threshold-surfaces"
 246  * pref plus the number of native sizes of the image. When in "factor of 2"
 247  * mode, the cache will strongly favour sizes which are a factor of 2 of the
 248  * largest native size. It accomplishes this by suggesting a factor of 2 size
 249  * when lookups fail and substituting the nearest factor of 2 surface to the
 250  * ideal size as the "best" available (as opposed to substitution but not
 251  * found). This allows us to minimize memory consumption and CPU time spent
 252  * decoding when a website requires many variants of the same surface.
 253  */
 254 class ImageSurfaceCache {
 255   ~ImageSurfaceCache() {}
 256
 257  public:
 258   explicit ImageSurfaceCache(const ImageKey aImageKey)
 259       : mLocked(false),
 260         mFactor2Mode(false),
 261         mFactor2Pruned(false),
 262         mIsVectorImage(aImageKey->GetType() == imgIContainer::TYPE_VECTOR) {}
 263
 264   MOZ_DECLARE_REFCOUNTED_TYPENAME(ImageSurfaceCache)
 265   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ImageSurfaceCache)
 266
 267   typedef nsRefPtrHashtable<nsGenericHashKey<SurfaceKey>, CachedSurface>
 268       SurfaceTable;
 269
 270   auto Values() const { return mSurfaces.Values(); }
 271   uint32_t Count() const { return mSurfaces.Count(); }
 272   bool IsEmpty() const { return mSurfaces.Count() == 0; }
 273
 274   size_t ShallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
 275     size_t bytes = aMallocSizeOf(this) +
 276                    mSurfaces.ShallowSizeOfExcludingThis(aMallocSizeOf);
 277     for (const auto& value : Values()) {
 278       bytes += value->ShallowSizeOfIncludingThis(aMallocSizeOf);
 279     }
 280     return bytes;
 281   }
 282
 283   [[nodiscard]] bool Insert(NotNull<CachedSurface*> aSurface) {
 284     MOZ_ASSERT(!mLocked || aSurface->IsPlaceholder() || aSurface->IsLocked(),
 285                "Inserting an unlocked surface for a locked image");
 286     const auto& surfaceKey = aSurface->GetSurfaceKey();
 287     if (surfaceKey.Region()) {
 288       // We don't allow substitutes for surfaces with regions, so we don't want
 289       // to allow factor of 2 mode pruning to release these surfaces.
 290       aSurface->SetCannotSubstitute();
 291     }
 292     return mSurfaces.InsertOrUpdate(surfaceKey, RefPtr<CachedSurface>{aSurface},
 293                                     fallible);
 294   }
 295
 296   already_AddRefed<CachedSurface> Remove(NotNull<CachedSurface*> aSurface) {
 297     MOZ_ASSERT(mSurfaces.GetWeak(aSurface->GetSurfaceKey()),
 298                "Should not be removing a surface we don't have");
 299
 300     RefPtr<CachedSurface> surface;
 301     mSurfaces.Remove(aSurface->GetSurfaceKey(), getter_AddRefs(surface));
 302     AfterMaybeRemove();
 303     return surface.forget();
 304   }
 305
 306   already_AddRefed<CachedSurface> Lookup(const SurfaceKey& aSurfaceKey,
 307                                          bool aForAccess) {
 308     RefPtr<CachedSurface> surface;
 309     mSurfaces.Get(aSurfaceKey, getter_AddRefs(surface));
 310
 311     if (aForAccess) {
 312       if (surface) {
 313         // We don't want to allow factor of 2 mode pruning to release surfaces
 314         // for which the callers will accept no substitute.
 315         surface->SetCannotSubstitute();
 316       } else if (!mFactor2Mode) {
 317         // If no exact match is found, and this is for use rather than internal
 318         // accounting (i.e. insert and removal), we know this will trigger a
 319         // decode. Make sure we switch now to factor of 2 mode if necessary.
 320         MaybeSetFactor2Mode();
 321       }
 322     }
 323
 324     return surface.forget();
 325   }
 326
 327   /**
 328    * @returns A tuple containing the best matching CachedSurface if available,
 329    *          a MatchType describing how the CachedSurface was selected, and
 330    *          an IntSize which is the size the caller should choose to decode
 331    *          at should it attempt to do so.
 332    */
 333   std::tuple<already_AddRefed<CachedSurface>, MatchType, IntSize>
 334   LookupBestMatch(const SurfaceKey& aIdealKey) {
 335     // Try for an exact match first.
 336     RefPtr<CachedSurface> exactMatch;
 337     mSurfaces.Get(aIdealKey, getter_AddRefs(exactMatch));
 338     if (exactMatch) {
 339       if (exactMatch->IsDecoded()) {
 340         return std::make_tuple(exactMatch.forget(), MatchType::EXACT,
 341                                IntSize());
 342       }
 343     } else if (aIdealKey.Region()) {
 344       // We cannot substitute if we have a region. Allow it to create an exact
 345       // match.
 346       return std::make_tuple(exactMatch.forget(), MatchType::NOT_FOUND,
 347                              IntSize());
 348     } else if (!mFactor2Mode) {
 349       // If no exact match is found, and we are not in factor of 2 mode, then
 350       // we know that we will trigger a decode because at best we will provide
 351       // a substitute. Make sure we switch now to factor of 2 mode if necessary.
 352       MaybeSetFactor2Mode();
 353     }
 354
 355     // Try for a best match second, if using compact.
 356     IntSize suggestedSize = SuggestedSize(aIdealKey.Size());
 357     if (suggestedSize != aIdealKey.Size()) {
 358       if (!exactMatch) {
 359         SurfaceKey compactKey = aIdealKey.CloneWithSize(suggestedSize);
 360         mSurfaces.Get(compactKey, getter_AddRefs(exactMatch));
 361         if (exactMatch && exactMatch->IsDecoded()) {
 362           MOZ_ASSERT(suggestedSize != aIdealKey.Size());
 363           return std::make_tuple(exactMatch.forget(),
 364                                  MatchType::SUBSTITUTE_BECAUSE_BEST,
 365                                  suggestedSize);
 366         }
 367       }
 368     }
 369
 370     // There's no perfect match, so find the best match we can.
 371     RefPtr<CachedSurface> bestMatch;
 372     for (const auto& value : Values()) {
 373       NotNull<CachedSurface*> current = WrapNotNull(value);
 374       const SurfaceKey& currentKey = current->GetSurfaceKey();
 375
 376       // We never match a placeholder or a surface with a region.
 377       if (current->IsPlaceholder() || currentKey.Region()) {
 378         continue;
 379       }
 380       // Matching the playback type and SVG context is required.
 381       if (currentKey.Playback() != aIdealKey.Playback() ||
 382           currentKey.SVGContext() != aIdealKey.SVGContext()) {
 383         continue;
 384       }
 385       // Matching the flags is required.
 386       if (currentKey.Flags() != aIdealKey.Flags()) {
 387         continue;
 388       }
 389       // Anything is better than nothing! (Within the constraints we just
 390       // checked, of course.)
 391       if (!bestMatch) {
 392         bestMatch = current;
 393         continue;
 394       }
 395
 396       MOZ_ASSERT(bestMatch, "Should have a current best match");
 397
 398       // Always prefer completely decoded surfaces.
 399       bool bestMatchIsDecoded = bestMatch->IsDecoded();
 400       if (bestMatchIsDecoded && !current->IsDecoded()) {
 401         continue;
 402       }
 403       if (!bestMatchIsDecoded && current->IsDecoded()) {
 404         bestMatch = current;
 405         continue;
 406       }
 407
 408       SurfaceKey bestMatchKey = bestMatch->GetSurfaceKey();
 409       if (CompareArea(aIdealKey.Size(), bestMatchKey.Size(),
 410                       currentKey.Size())) {
 411         bestMatch = current;
 412       }
 413     }
 414
 415     MatchType matchType;
 416     if (bestMatch) {
 417       if (!exactMatch) {
 418         // No exact match, neither ideal nor factor of 2.
 419         MOZ_ASSERT(suggestedSize != bestMatch->GetSurfaceKey().Size(),
 420                    "No exact match despite the fact the sizes match!");
 421         matchType = MatchType::SUBSTITUTE_BECAUSE_NOT_FOUND;
 422       } else if (exactMatch != bestMatch) {
 423         // The exact match is still decoding, but we found a substitute.
 424         matchType = MatchType::SUBSTITUTE_BECAUSE_PENDING;
 425       } else if (aIdealKey.Size() != bestMatch->GetSurfaceKey().Size()) {
 426         // The best factor of 2 match is still decoding, but the best we've got.
 427         MOZ_ASSERT(suggestedSize != aIdealKey.Size());
 428         MOZ_ASSERT(mFactor2Mode || mIsVectorImage);
 429         matchType = MatchType::SUBSTITUTE_BECAUSE_BEST;
 430       } else {
 431         // The exact match is still decoding, but it's the best we've got.
 432         matchType = MatchType::EXACT;
 433       }
 434     } else {
 435       if (exactMatch) {
 436         // We found an "exact match"; it must have been a placeholder.
 437         MOZ_ASSERT(exactMatch->IsPlaceholder());
 438         matchType = MatchType::PENDING;
 439       } else {
 440         // We couldn't find an exact match *or* a substitute.
 441         matchType = MatchType::NOT_FOUND;
 442       }
 443     }
 444
 445     return std::make_tuple(bestMatch.forget(), matchType, suggestedSize);
 446   }
 447
 448   void MaybeSetFactor2Mode() {
 449     MOZ_ASSERT(!mFactor2Mode);
 450
 451     // Typically an image cache will not have too many size-varying surfaces, so
 452     // if we exceed the given threshold, we should consider using a subset.
 453     int32_t thresholdSurfaces =
 454         StaticPrefs::image_cache_factor2_threshold_surfaces();
 455     if (thresholdSurfaces < 0 ||
 456         mSurfaces.Count() <= static_cast<uint32_t>(thresholdSurfaces)) {
 457       return;
 458     }
 459
 460     // Determine how many native surfaces this image has. If it is zero, and it
 461     // is a vector image, then we should impute a single native size. Otherwise,
 462     // it may be zero because we don't know yet, or the image has an error, or
 463     // it isn't supported.
 464     NotNull<CachedSurface*> current =
 465         WrapNotNull(mSurfaces.ConstIter().UserData());
 466     Image* image = static_cast<Image*>(current->GetImageKey());
 467     size_t nativeSizes = image->GetNativeSizesLength();
 468     if (mIsVectorImage) {
 469       MOZ_ASSERT(nativeSizes == 0);
 470       nativeSizes = 1;
 471     } else if (nativeSizes == 0) {
 472       return;
 473     }
 474
 475     // Increase the threshold by the number of native sizes. This ensures that
 476     // we do not prevent decoding of the image at all its native sizes. It does
 477     // not guarantee we will provide a surface at that size however (i.e. many
 478     // other sized surfaces are requested, in addition to the native sizes).
 479     thresholdSurfaces += nativeSizes;
 480     if (mSurfaces.Count() <= static_cast<uint32_t>(thresholdSurfaces)) {
 481       return;
 482     }
 483
 484     // We have a valid size, we can change modes.
 485     mFactor2Mode = true;
 486   }
 487
 488   template <typename Function>
 489   void Prune(Function&& aRemoveCallback) {
 490     if (!mFactor2Mode || mFactor2Pruned) {
 491       return;
 492     }
 493
 494     // Attempt to discard any surfaces which are not factor of 2 and the best
 495     // factor of 2 match exists.
 496     bool hasNotFactorSize = false;
 497     for (auto iter = mSurfaces.Iter(); !iter.Done(); iter.Next()) {
 498       NotNull<CachedSurface*> current = WrapNotNull(iter.UserData());
 499       const SurfaceKey& currentKey = current->GetSurfaceKey();
 500       const IntSize& currentSize = currentKey.Size();
 501
 502       // First we check if someone requested this size and would not accept
 503       // an alternatively sized surface.
 504       if (current->CannotSubstitute()) {
 505         continue;
 506       }
 507
 508       // Next we find the best factor of 2 size for this surface. If this
 509       // surface is a factor of 2 size, then we want to keep it.
 510       IntSize bestSize = SuggestedSize(currentSize);
 511       if (bestSize == currentSize) {
 512         continue;
 513       }
 514
 515       // Check the cache for a surface with the same parameters except for the
 516       // size which uses the closest factor of 2 size.
 517       SurfaceKey compactKey = currentKey.CloneWithSize(bestSize);
 518       RefPtr<CachedSurface> compactMatch;
 519       mSurfaces.Get(compactKey, getter_AddRefs(compactMatch));
 520       if (compactMatch && compactMatch->IsDecoded()) {
 521         aRemoveCallback(current);
 522         iter.Remove();
 523       } else {
 524         hasNotFactorSize = true;
 525       }
 526     }
 527
 528     // We have no surfaces that are not factor of 2 sized, so we can stop
 529     // pruning henceforth, because we avoid the insertion of new surfaces that
 530     // don't match our sizing set (unless the caller won't accept a
 531     // substitution.)
 532     if (!hasNotFactorSize) {
 533       mFactor2Pruned = true;
 534     }
 535
 536     // We should never leave factor of 2 mode due to pruning in of itself, but
 537     // if we discarded surfaces due to the volatile buffers getting released,
 538     // it is possible.
 539     AfterMaybeRemove();
 540   }
 541
 542   template <typename Function>
 543   bool Invalidate(Function&& aRemoveCallback) {
 544     // Remove all non-blob recordings from the cache. Invalidate any blob
 545     // recordings.
 546     bool foundRecording = false;
 547     for (auto iter = mSurfaces.Iter(); !iter.Done(); iter.Next()) {
 548       NotNull<CachedSurface*> current = WrapNotNull(iter.UserData());
 549
 550       if (current->GetSurfaceKey().Flags() & SurfaceFlags::RECORD_BLOB) {
 551         foundRecording = true;
 552         current->InvalidateRecording();
 553         continue;
 554       }
 555
 556       aRemoveCallback(current);
 557       iter.Remove();
 558     }
 559
 560     AfterMaybeRemove();
 561     return foundRecording;
 562   }
 563
 564   IntSize SuggestedSize(const IntSize& aSize) const {
 565     IntSize suggestedSize = SuggestedSizeInternal(aSize);
 566     if (mIsVectorImage) {
 567       suggestedSize = SurfaceCache::ClampVectorSize(suggestedSize);
 568     }
 569     return suggestedSize;
 570   }
 571
 572   IntSize SuggestedSizeInternal(const IntSize& aSize) const {
 573     // When not in factor of 2 mode, we can always decode at the given size.
 574     if (!mFactor2Mode) {
 575       return aSize;
 576     }
 577
 578     // We cannot enter factor of 2 mode unless we have a minimum number of
 579     // surfaces, and we should have left it if the cache was emptied.
 580     if (MOZ_UNLIKELY(IsEmpty())) {
 581       MOZ_ASSERT_UNREACHABLE("Should not be empty and in factor of 2 mode!");
 582       return aSize;
 583     }
 584
 585     // This bit of awkwardness gets the largest native size of the image.
 586     NotNull<CachedSurface*> firstSurface =
 587         WrapNotNull(mSurfaces.ConstIter().UserData());
 588     Image* image = static_cast<Image*>(firstSurface->GetImageKey());
 589     IntSize factorSize;
 590     if (NS_FAILED(image->GetWidth(&factorSize.width)) ||
 591         NS_FAILED(image->GetHeight(&factorSize.height)) ||
 592         factorSize.IsEmpty()) {
 593       // Valid vector images may have a default size of 0x0. In that case, just
 594       // assume a default size of 100x100 and apply the intrinsic ratio if
 595       // available. If our guess was too small, don't use factor-of-scaling.
 596       MOZ_ASSERT(mIsVectorImage);
 597       factorSize = IntSize(100, 100);
 598       Maybe<AspectRatio> aspectRatio = image->GetIntrinsicRatio();
 599       if (aspectRatio && *aspectRatio) {
 600         factorSize.width =
 601             NSToIntRound(aspectRatio->ApplyToFloat(float(factorSize.height)));
 602         if (factorSize.IsEmpty()) {
 603           return aSize;
 604         }
 605       }
 606     }
 607
 608     if (mIsVectorImage) {
 609       // Ensure the aspect ratio matches the native size before forcing the
 610       // caller to accept a factor of 2 size. The difference between the aspect
 611       // ratios is:
 612       //
 613       //     delta = nativeWidth/nativeHeight - desiredWidth/desiredHeight
 614       //
 615       //     delta*nativeHeight*desiredHeight = nativeWidth*desiredHeight
 616       //                                      - desiredWidth*nativeHeight
 617       //
 618       // Using the maximum accepted delta as a constant, we can avoid the
 619       // floating point division and just compare after some integer ops.
 620       int32_t delta =
 621           factorSize.width * aSize.height - aSize.width * factorSize.height;
 622       int32_t maxDelta = (factorSize.height * aSize.height) >> 4;
 623       if (delta > maxDelta || delta < -maxDelta) {
 624         return aSize;
 625       }
 626
 627       // If the requested size is bigger than the native size, we actually need
 628       // to grow the native size instead of shrinking it.
 629       if (factorSize.width < aSize.width) {
 630         do {
 631           IntSize candidate(factorSize.width * 2, factorSize.height * 2);
 632           if (!SurfaceCache::IsLegalSize(candidate)) {
 633             break;
 634           }
 635
 636           factorSize = candidate;
 637         } while (factorSize.width < aSize.width);
 638
 639         return factorSize;
 640       }
 641
 642       // Otherwise we can find the best fit as normal.
 643     }
 644
 645     // Start with the native size as the best first guess.
 646     IntSize bestSize = factorSize;
 647     factorSize.width /= 2;
 648     factorSize.height /= 2;
 649
 650     while (!factorSize.IsEmpty()) {
 651       if (!CompareArea(aSize, bestSize, factorSize)) {
 652         // This size is not better than the last. Since we proceed from largest
 653         // to smallest, we know that the next size will not be better if the
 654         // previous size was rejected. Break early.
 655         break;
 656       }
 657
 658       // The current factor of 2 size is better than the last selected size.
 659       bestSize = factorSize;
 660       factorSize.width /= 2;
 661       factorSize.height /= 2;
 662     }
 663
 664     return bestSize;
 665   }
 666
 667   bool CompareArea(const IntSize& aIdealSize, const IntSize& aBestSize,
 668                    const IntSize& aSize) const {
 669     // Compare sizes. We use an area-based heuristic here instead of computing a
 670     // truly optimal answer, since it seems very unlikely to make a difference
 671     // for realistic sizes.
 672     int64_t idealArea = AreaOfIntSize(aIdealSize);
 673     int64_t currentArea = AreaOfIntSize(aSize);
 674     int64_t bestMatchArea = AreaOfIntSize(aBestSize);
 675
 676     // If the best match is smaller than the ideal size, prefer bigger sizes.
 677     if (bestMatchArea < idealArea) {
 678       if (currentArea > bestMatchArea) {
 679         return true;
 680       }
 681       return false;
 682     }
 683
 684     // Other, prefer sizes closer to the ideal size, but still not smaller.
 685     if (idealArea <= currentArea && currentArea < bestMatchArea) {
 686       return true;
 687     }
 688
 689     // This surface isn't an improvement over the current best match.
 690     return false;
 691   }
 692
 693   template <typename Function>
 694   void CollectSizeOfSurfaces(nsTArray<SurfaceMemoryCounter>& aCounters,
 695                              MallocSizeOf aMallocSizeOf,
 696                              Function&& aRemoveCallback) {
 697     CachedSurface::SurfaceMemoryReport report(aCounters, aMallocSizeOf);
 698     for (auto iter = mSurfaces.Iter(); !iter.Done(); iter.Next()) {
 699       NotNull<CachedSurface*> surface = WrapNotNull(iter.UserData());
 700
 701       // We don't need the drawable surface for ourselves, but adding a surface
 702       // to the report will trigger this indirectly. If the surface was
 703       // discarded by the OS because it was in volatile memory, we should remove
 704       // it from the cache immediately rather than include it in the report.
 705       DrawableSurface drawableSurface;
 706       if (!surface->IsPlaceholder()) {
 707         drawableSurface = surface->GetDrawableSurface();
 708         if (!drawableSurface) {
 709           aRemoveCallback(surface);
 710           iter.Remove();
 711           continue;
 712         }
 713       }
 714
 715       const IntSize& size = surface->GetSurfaceKey().Size();
 716       bool factor2Size = false;
 717       if (mFactor2Mode) {
 718         factor2Size = (size == SuggestedSize(size));
 719       }
 720       report.Add(surface, factor2Size);
 721     }
 722
 723     AfterMaybeRemove();
 724   }
 725
 726   void SetLocked(bool aLocked) { mLocked = aLocked; }
 727   bool IsLocked() const { return mLocked; }
 728
 729  private:
 730   void AfterMaybeRemove() {
 731     if (IsEmpty() && mFactor2Mode) {
 732       // The last surface for this cache was removed. This can happen if the
 733       // surface was stored in a volatile buffer and got purged, or the surface
 734       // expired from the cache. If the cache itself lingers for some reason
 735       // (e.g. in the process of performing a lookup, the cache itself is
 736       // locked), then we need to reset the factor of 2 state because it
 737       // requires at least one surface present to get the native size
 738       // information from the image.
 739       mFactor2Mode = mFactor2Pruned = false;
 740     }
 741   }
 742
 743   SurfaceTable mSurfaces;
 744
 745   bool mLocked;
 746
 747   // True in "factor of 2" mode.
 748   bool mFactor2Mode;
 749
 750   // True if all non-factor of 2 surfaces have been removed from the cache. Note
 751   // that this excludes unsubstitutable sizes.
 752   bool mFactor2Pruned;
 753
 754   // True if the surfaces are produced from a vector image. If so, it must match
 755   // the aspect ratio when using factor of 2 mode.
 756   bool mIsVectorImage;
 757 };
 758
 759 /**
 760  * SurfaceCacheImpl is responsible for determining which surfaces will be cached
 761  * and managing the surface cache data structures. Rather than interact with
 762  * SurfaceCacheImpl directly, client code interacts with SurfaceCache, which
 763  * maintains high-level invariants and encapsulates the details of the surface
 764  * cache's implementation.
 765  */
 766 class SurfaceCacheImpl final : public nsIMemoryReporter {
 767  public:
 768   NS_DECL_ISUPPORTS
 769
 770   SurfaceCacheImpl(uint32_t aSurfaceCacheExpirationTimeMS,
 771                    uint32_t aSurfaceCacheDiscardFactor,
 772                    uint32_t aSurfaceCacheSize)
 773       : mExpirationTracker(aSurfaceCacheExpirationTimeMS),
 774         mMemoryPressureObserver(new MemoryPressureObserver),
 775         mDiscardFactor(aSurfaceCacheDiscardFactor),
 776         mMaxCost(aSurfaceCacheSize),
 777         mAvailableCost(aSurfaceCacheSize),
 778         mLockedCost(0),
 779         mOverflowCount(0),
 780         mAlreadyPresentCount(0),
 781         mTableFailureCount(0),
 782         mTrackingFailureCount(0) {
 783     nsCOMPtr<nsIObserverService> os = services::GetObserverService();
 784     if (os) {
 785       os->AddObserver(mMemoryPressureObserver, "memory-pressure", false);
 786     }
 787   }
 788
 789  private:
 790   virtual ~SurfaceCacheImpl() {
 791     nsCOMPtr<nsIObserverService> os = services::GetObserverService();
 792     if (os) {
 793       os->RemoveObserver(mMemoryPressureObserver, "memory-pressure");
 794     }
 795
 796     UnregisterWeakMemoryReporter(this);
 797   }
 798
 799  public:
 800   void InitMemoryReporter() { RegisterWeakMemoryReporter(this); }
 801
 802   InsertOutcome Insert(NotNull<ISurfaceProvider*> aProvider, bool aSetAvailable,
 803                        const StaticMutexAutoLock& aAutoLock) {
 804     // If this is a duplicate surface, refuse to replace the original.
 805     // XXX(seth): Calling Lookup() and then RemoveEntry() does the lookup
 806     // twice. We'll make this more efficient in bug 1185137.
 807     LookupResult result =
 808         Lookup(aProvider->GetImageKey(), aProvider->GetSurfaceKey(), aAutoLock,
 809                /* aMarkUsed = */ false);
 810     if (MOZ_UNLIKELY(result)) {
 811       mAlreadyPresentCount++;
 812       return InsertOutcome::FAILURE_ALREADY_PRESENT;
 813     }
 814
 815     if (result.Type() == MatchType::PENDING) {
 816       RemoveEntry(aProvider->GetImageKey(), aProvider->GetSurfaceKey(),
 817                   aAutoLock);
 818     }
 819
 820     MOZ_ASSERT(result.Type() == MatchType::NOT_FOUND ||
 821                    result.Type() == MatchType::PENDING,
 822                "A LookupResult with no surface should be NOT_FOUND or PENDING");
 823
 824     // If this is bigger than we can hold after discarding everything we can,
 825     // refuse to cache it.
 826     Cost cost = aProvider->LogicalSizeInBytes();
 827     if (MOZ_UNLIKELY(!CanHoldAfterDiscarding(cost))) {
 828       mOverflowCount++;
 829       return InsertOutcome::FAILURE;
 830     }
 831
 832     // Remove elements in order of cost until we can fit this in the cache. Note
 833     // that locked surfaces aren't in mCosts, so we never remove them here.
 834     while (cost > mAvailableCost) {
 835       MOZ_ASSERT(!mCosts.IsEmpty(),
 836                  "Removed everything and it still won't fit");
 837       Remove(mCosts.LastElement().Surface(), /* aStopTracking */ true,
 838              aAutoLock);
 839     }
 840
 841     // Locate the appropriate per-image cache. If there's not an existing cache
 842     // for this image, create it.
 843     const ImageKey imageKey = aProvider->GetImageKey();
 844     RefPtr<ImageSurfaceCache> cache = GetImageCache(imageKey);
 845     if (!cache) {
 846       cache = new ImageSurfaceCache(imageKey);
 847       if (!mImageCaches.InsertOrUpdate(aProvider->GetImageKey(), RefPtr{cache},
 848                                        fallible)) {
 849         mTableFailureCount++;
 850         return InsertOutcome::FAILURE;
 851       }
 852     }
 853
 854     // If we were asked to mark the cache entry available, do so.
 855     if (aSetAvailable) {
 856       aProvider->Availability().SetAvailable();
 857     }
 858
 859     auto surface = MakeNotNull<RefPtr<CachedSurface>>(aProvider);
 860
 861     // We require that locking succeed if the image is locked and we're not
 862     // inserting a placeholder; the caller may need to know this to handle
 863     // errors correctly.
 864     bool mustLock = cache->IsLocked() && !surface->IsPlaceholder();
 865     if (mustLock) {
 866       surface->SetLocked(true);
 867       if (!surface->IsLocked()) {
 868         return InsertOutcome::FAILURE;
 869       }
 870     }
 871
 872     // Insert.
 873     MOZ_ASSERT(cost <= mAvailableCost, "Inserting despite too large a cost");
 874     if (!cache->Insert(surface)) {
 875       mTableFailureCount++;
 876       if (mustLock) {
 877         surface->SetLocked(false);
 878       }
 879       return InsertOutcome::FAILURE;
 880     }
 881
 882     if (MOZ_UNLIKELY(!StartTracking(surface, aAutoLock))) {
 883       MOZ_ASSERT(!mustLock);
 884       Remove(surface, /* aStopTracking */ false, aAutoLock);
 885       return InsertOutcome::FAILURE;
 886     }
 887
 888     return InsertOutcome::SUCCESS;
 889   }
 890
 891   void Remove(NotNull<CachedSurface*> aSurface, bool aStopTracking,
 892               const StaticMutexAutoLock& aAutoLock) {
 893     ImageKey imageKey = aSurface->GetImageKey();
 894
 895     RefPtr<ImageSurfaceCache> cache = GetImageCache(imageKey);
 896     MOZ_ASSERT(cache, "Shouldn't try to remove a surface with no image cache");
 897
 898     // If the surface was not a placeholder, tell its image that we discarded
 899     // it.
 900     if (!aSurface->IsPlaceholder()) {
 901       static_cast<Image*>(imageKey)->OnSurfaceDiscarded(
 902           aSurface->GetSurfaceKey());
 903     }
 904
 905     // If we failed during StartTracking, we can skip this step.
 906     if (aStopTracking) {
 907       StopTracking(aSurface, /* aIsTracked */ true, aAutoLock);
 908     }
 909
 910     // Individual surfaces must be freed outside the lock.
 911     mCachedSurfacesDiscard.AppendElement(cache->Remove(aSurface));
 912
 913     MaybeRemoveEmptyCache(imageKey, cache);
 914   }
 915
 916   bool StartTracking(NotNull<CachedSurface*> aSurface,
 917                      const StaticMutexAutoLock& aAutoLock) {
 918     CostEntry costEntry = aSurface->GetCostEntry();
 919     MOZ_ASSERT(costEntry.GetCost() <= mAvailableCost,
 920                "Cost too large and the caller didn't catch it");
 921
 922     if (aSurface->IsLocked()) {
 923       mLockedCost += costEntry.GetCost();
 924       MOZ_ASSERT(mLockedCost <= mMaxCost, "Locked more than we can hold?");
 925     } else {
 926       if (NS_WARN_IF(!mCosts.InsertElementSorted(costEntry, fallible))) {
 927         mTrackingFailureCount++;
 928         return false;
 929       }
 930
 931       // This may fail during XPCOM shutdown, so we need to ensure the object is
 932       // tracked before calling RemoveObject in StopTracking.
 933       nsresult rv = mExpirationTracker.AddObjectLocked(aSurface, aAutoLock);
 934       if (NS_WARN_IF(NS_FAILED(rv))) {
 935         DebugOnly<bool> foundInCosts = mCosts.RemoveElementSorted(costEntry);
 936         MOZ_ASSERT(foundInCosts, "Lost track of costs for this surface");
 937         mTrackingFailureCount++;
 938         return false;
 939       }
 940     }
 941
 942     mAvailableCost -= costEntry.GetCost();
 943     return true;
 944   }
 945
 946   void StopTracking(NotNull<CachedSurface*> aSurface, bool aIsTracked,
 947                     const StaticMutexAutoLock& aAutoLock) {
 948     CostEntry costEntry = aSurface->GetCostEntry();
 949
 950     if (aSurface->IsLocked()) {
 951       MOZ_ASSERT(mLockedCost >= costEntry.GetCost(), "Costs don't balance");
 952       mLockedCost -= costEntry.GetCost();
 953       // XXX(seth): It'd be nice to use an O(log n) lookup here. This is O(n).
 954       MOZ_ASSERT(!mCosts.Contains(costEntry),
 955                  "Shouldn't have a cost entry for a locked surface");
 956     } else {
 957       if (MOZ_LIKELY(aSurface->GetExpirationState()->IsTracked())) {
 958         MOZ_ASSERT(aIsTracked, "Expiration-tracking a surface unexpectedly!");
 959         mExpirationTracker.RemoveObjectLocked(aSurface, aAutoLock);
 960       } else {
 961         // Our call to AddObject must have failed in StartTracking; most likely
 962         // we're in XPCOM shutdown right now.
 963         MOZ_ASSERT(!aIsTracked, "Not expiration-tracking an unlocked surface!");
 964       }
 965
 966       DebugOnly<bool> foundInCosts = mCosts.RemoveElementSorted(costEntry);
 967       MOZ_ASSERT(foundInCosts, "Lost track of costs for this surface");
 968     }
 969
 970     mAvailableCost += costEntry.GetCost();
 971     MOZ_ASSERT(mAvailableCost <= mMaxCost,
 972                "More available cost than we started with");
 973   }
 974
 975   LookupResult Lookup(const ImageKey aImageKey, const SurfaceKey& aSurfaceKey,
 976                       const StaticMutexAutoLock& aAutoLock, bool aMarkUsed) {
 977     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
 978     if (!cache) {
 979       // No cached surfaces for this image.
 980       return LookupResult(MatchType::NOT_FOUND);
 981     }
 982
 983     RefPtr<CachedSurface> surface = cache->Lookup(aSurfaceKey, aMarkUsed);
 984     if (!surface) {
 985       // Lookup in the per-image cache missed.
 986       return LookupResult(MatchType::NOT_FOUND);
 987     }
 988
 989     if (surface->IsPlaceholder()) {
 990       return LookupResult(MatchType::PENDING);
 991     }
 992
 993     DrawableSurface drawableSurface = surface->GetDrawableSurface();
 994     if (!drawableSurface) {
 995       // The surface was released by the operating system. Remove the cache
 996       // entry as well.
 997       Remove(WrapNotNull(surface), /* aStopTracking */ true, aAutoLock);
 998       return LookupResult(MatchType::NOT_FOUND);
 999     }
1000
1001     if (aMarkUsed &&
1002         !MarkUsed(WrapNotNull(surface), WrapNotNull(cache), aAutoLock)) {
1003       Remove(WrapNotNull(surface), /* aStopTracking */ false, aAutoLock);
1004       return LookupResult(MatchType::NOT_FOUND);
1005     }
1006
1007     MOZ_ASSERT(surface->GetSurfaceKey() == aSurfaceKey,
1008                "Lookup() not returning an exact match?");
1009     return LookupResult(std::move(drawableSurface), MatchType::EXACT);
1010   }
1011
1012   LookupResult LookupBestMatch(const ImageKey aImageKey,
1013                                const SurfaceKey& aSurfaceKey,
1014                                const StaticMutexAutoLock& aAutoLock,
1015                                bool aMarkUsed) {
1016     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1017     if (!cache) {
1018       // No cached surfaces for this image.
1019       return LookupResult(
1020           MatchType::NOT_FOUND,
1021           SurfaceCache::ClampSize(aImageKey, aSurfaceKey.Size()));
1022     }
1023
1024     // Repeatedly look up the best match, trying again if the resulting surface
1025     // has been freed by the operating system, until we can either lock a
1026     // surface for drawing or there are no matching surfaces left.
1027     // XXX(seth): This is O(N^2), but N is expected to be very small. If we
1028     // encounter a performance problem here we can revisit this.
1029
1030     RefPtr<CachedSurface> surface;
1031     DrawableSurface drawableSurface;
1032     MatchType matchType = MatchType::NOT_FOUND;
1033     IntSize suggestedSize;
1034     while (true) {
1035       std::tie(surface, matchType, suggestedSize) =
1036           cache->LookupBestMatch(aSurfaceKey);
1037
1038       if (!surface) {
1039         return LookupResult(
1040             matchType, suggestedSize);  // Lookup in the per-image cache missed.
1041       }
1042
1043       drawableSurface = surface->GetDrawableSurface();
1044       if (drawableSurface) {
1045         break;
1046       }
1047
1048       // The surface was released by the operating system. Remove the cache
1049       // entry as well.
1050       Remove(WrapNotNull(surface), /* aStopTracking */ true, aAutoLock);
1051     }
1052
1053     MOZ_ASSERT_IF(matchType == MatchType::EXACT,
1054                   surface->GetSurfaceKey() == aSurfaceKey);
1055     MOZ_ASSERT_IF(
1056         matchType == MatchType::SUBSTITUTE_BECAUSE_NOT_FOUND ||
1057             matchType == MatchType::SUBSTITUTE_BECAUSE_PENDING,
1058         surface->GetSurfaceKey().Region() == aSurfaceKey.Region() &&
1059             surface->GetSurfaceKey().SVGContext() == aSurfaceKey.SVGContext() &&
1060             surface->GetSurfaceKey().Playback() == aSurfaceKey.Playback() &&
1061             surface->GetSurfaceKey().Flags() == aSurfaceKey.Flags());
1062
1063     if (matchType == MatchType::EXACT ||
1064         matchType == MatchType::SUBSTITUTE_BECAUSE_BEST) {
1065       if (aMarkUsed &&
1066           !MarkUsed(WrapNotNull(surface), WrapNotNull(cache), aAutoLock)) {
1067         Remove(WrapNotNull(surface), /* aStopTracking */ false, aAutoLock);
1068       }
1069     }
1070
1071     return LookupResult(std::move(drawableSurface), matchType, suggestedSize);
1072   }
1073
1074   bool CanHold(const Cost aCost) const { return aCost <= mMaxCost; }
1075
1076   size_t MaximumCapacity() const { return size_t(mMaxCost); }
1077
1078   void SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider,
1079                         const StaticMutexAutoLock& aAutoLock) {
1080     if (!aProvider->Availability().IsPlaceholder()) {
1081       MOZ_ASSERT_UNREACHABLE("Calling SurfaceAvailable on non-placeholder");
1082       return;
1083     }
1084
1085     // Reinsert the provider, requesting that Insert() mark it available. This
1086     // may or may not succeed, depending on whether some other decoder has
1087     // beaten us to the punch and inserted a non-placeholder version of this
1088     // surface first, but it's fine either way.
1089     // XXX(seth): This could be implemented more efficiently; we should be able
1090     // to just update our data structures without reinserting.
1091     Insert(aProvider, /* aSetAvailable = */ true, aAutoLock);
1092   }
1093
1094   void LockImage(const ImageKey aImageKey) {
1095     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1096     if (!cache) {
1097       cache = new ImageSurfaceCache(aImageKey);
1098       mImageCaches.InsertOrUpdate(aImageKey, RefPtr{cache});
1099     }
1100
1101     cache->SetLocked(true);
1102
1103     // We don't relock this image's existing surfaces right away; instead, the
1104     // image should arrange for Lookup() to touch them if they are still useful.
1105   }
1106
1107   void UnlockImage(const ImageKey aImageKey,
1108                    const StaticMutexAutoLock& aAutoLock) {
1109     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1110     if (!cache || !cache->IsLocked()) {
1111       return;  // Already unlocked.
1112     }
1113
1114     cache->SetLocked(false);
1115     DoUnlockSurfaces(WrapNotNull(cache), /* aStaticOnly = */ false, aAutoLock);
1116   }
1117
1118   void UnlockEntries(const ImageKey aImageKey,
1119                      const StaticMutexAutoLock& aAutoLock) {
1120     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1121     if (!cache || !cache->IsLocked()) {
1122       return;  // Already unlocked.
1123     }
1124
1125     // (Note that we *don't* unlock the per-image cache here; that's the
1126     // difference between this and UnlockImage.)
1127     DoUnlockSurfaces(WrapNotNull(cache),
1128                      /* aStaticOnly = */
1129                      !StaticPrefs::image_mem_animated_discardable_AtStartup(),
1130                      aAutoLock);
1131   }
1132
1133   already_AddRefed<ImageSurfaceCache> RemoveImage(
1134       const ImageKey aImageKey, const StaticMutexAutoLock& aAutoLock) {
1135     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1136     if (!cache) {
1137       return nullptr;  // No cached surfaces for this image, so nothing to do.
1138     }
1139
1140     // Discard all of the cached surfaces for this image.
1141     // XXX(seth): This is O(n^2) since for each item in the cache we are
1142     // removing an element from the costs array. Since n is expected to be
1143     // small, performance should be good, but if usage patterns change we should
1144     // change the data structure used for mCosts.
1145     for (const auto& value : cache->Values()) {
1146       StopTracking(WrapNotNull(value),
1147                    /* aIsTracked */ true, aAutoLock);
1148     }
1149
1150     // The per-image cache isn't needed anymore, so remove it as well.
1151     // This implicitly unlocks the image if it was locked.
1152     mImageCaches.Remove(aImageKey);
1153
1154     // Since we did not actually remove any of the surfaces from the cache
1155     // itself, only stopped tracking them, we should free it outside the lock.
1156     return cache.forget();
1157   }
1158
1159   void PruneImage(const ImageKey aImageKey,
1160                   const StaticMutexAutoLock& aAutoLock) {
1161     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1162     if (!cache) {
1163       return;  // No cached surfaces for this image, so nothing to do.
1164     }
1165
1166     cache->Prune([this, &aAutoLock](NotNull<CachedSurface*> aSurface) -> void {
1167       StopTracking(aSurface, /* aIsTracked */ true, aAutoLock);
1168       // Individual surfaces must be freed outside the lock.
1169       mCachedSurfacesDiscard.AppendElement(aSurface);
1170     });
1171
1172     MaybeRemoveEmptyCache(aImageKey, cache);
1173   }
1174
1175   bool InvalidateImage(const ImageKey aImageKey,
1176                        const StaticMutexAutoLock& aAutoLock) {
1177     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1178     if (!cache) {
1179       return false;  // No cached surfaces for this image, so nothing to do.
1180     }
1181
1182     bool rv = cache->Invalidate(
1183         [this, &aAutoLock](NotNull<CachedSurface*> aSurface) -> void {
1184           StopTracking(aSurface, /* aIsTracked */ true, aAutoLock);
1185           // Individual surfaces must be freed outside the lock.
1186           mCachedSurfacesDiscard.AppendElement(aSurface);
1187         });
1188
1189     MaybeRemoveEmptyCache(aImageKey, cache);
1190     return rv;
1191   }
1192
1193   void DiscardAll(const StaticMutexAutoLock& aAutoLock) {
1194     // Remove in order of cost because mCosts is an array and the other data
1195     // structures are all hash tables. Note that locked surfaces are not
1196     // removed, since they aren't present in mCosts.
1197     while (!mCosts.IsEmpty()) {
1198       Remove(mCosts.LastElement().Surface(), /* aStopTracking */ true,
1199              aAutoLock);
1200     }
1201   }
1202
1203   void DiscardForMemoryPressure(const StaticMutexAutoLock& aAutoLock) {
1204     // Compute our discardable cost. Since locked surfaces aren't discardable,
1205     // we exclude them.
1206     const Cost discardableCost = (mMaxCost - mAvailableCost) - mLockedCost;
1207     MOZ_ASSERT(discardableCost <= mMaxCost, "Discardable cost doesn't add up");
1208
1209     // Our target is to raise our available cost by (1 / mDiscardFactor) of our
1210     // discardable cost - in other words, we want to end up with about
1211     // (discardableCost / mDiscardFactor) fewer bytes stored in the surface
1212     // cache after we're done.
1213     const Cost targetCost = mAvailableCost + (discardableCost / mDiscardFactor);
1214
1215     if (targetCost > mMaxCost - mLockedCost) {
1216       MOZ_ASSERT_UNREACHABLE("Target cost is more than we can discard");
1217       DiscardAll(aAutoLock);
1218       return;
1219     }
1220
1221     // Discard surfaces until we've reduced our cost to our target cost.
1222     while (mAvailableCost < targetCost) {
1223       MOZ_ASSERT(!mCosts.IsEmpty(), "Removed everything and still not done");
1224       Remove(mCosts.LastElement().Surface(), /* aStopTracking */ true,
1225              aAutoLock);
1226     }
1227   }
1228
1229   void TakeDiscard(nsTArray<RefPtr<CachedSurface>>& aDiscard,
1230                    const StaticMutexAutoLock& aAutoLock) {
1231     MOZ_ASSERT(aDiscard.IsEmpty());
1232     aDiscard = std::move(mCachedSurfacesDiscard);
1233   }
1234
1235   already_AddRefed<CachedSurface> GetSurfaceForResetAnimation(
1236       const ImageKey aImageKey, const SurfaceKey& aSurfaceKey,
1237       const StaticMutexAutoLock& aAutoLock) {
1238     RefPtr<CachedSurface> surface;
1239
1240     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1241     if (!cache) {
1242       // No cached surfaces for this image.
1243       return surface.forget();
1244     }
1245
1246     surface = cache->Lookup(aSurfaceKey, /* aForAccess = */ false);
1247     return surface.forget();
1248   }
1249
1250   void LockSurface(NotNull<CachedSurface*> aSurface,
1251                    const StaticMutexAutoLock& aAutoLock) {
1252     if (aSurface->IsPlaceholder() || aSurface->IsLocked()) {
1253       return;
1254     }
1255
1256     StopTracking(aSurface, /* aIsTracked */ true, aAutoLock);
1257
1258     // Lock the surface. This can fail.
1259     aSurface->SetLocked(true);
1260     DebugOnly<bool> tracked = StartTracking(aSurface, aAutoLock);
1261     MOZ_ASSERT(tracked);
1262   }
1263
1264   size_t ShallowSizeOfIncludingThis(
1265       MallocSizeOf aMallocSizeOf, const StaticMutexAutoLock& aAutoLock) const {
1266     size_t bytes =
1267         aMallocSizeOf(this) + mCosts.ShallowSizeOfExcludingThis(aMallocSizeOf) +
1268         mImageCaches.ShallowSizeOfExcludingThis(aMallocSizeOf) +
1269         mCachedSurfacesDiscard.ShallowSizeOfExcludingThis(aMallocSizeOf) +
1270         mExpirationTracker.ShallowSizeOfExcludingThis(aMallocSizeOf);
1271     for (const auto& data : mImageCaches.Values()) {
1272       bytes += data->ShallowSizeOfIncludingThis(aMallocSizeOf);
1273     }
1274     return bytes;
1275   }
1276
1277   NS_IMETHOD
1278   CollectReports(nsIHandleReportCallback* aHandleReport, nsISupports* aData,
1279                  bool aAnonymize) override {
1280     StaticMutexAutoLock lock(sInstanceMutex);
1281
1282     uint32_t lockedImageCount = 0;
1283     uint32_t totalSurfaceCount = 0;
1284     uint32_t lockedSurfaceCount = 0;
1285     for (const auto& cache : mImageCaches.Values()) {
1286       totalSurfaceCount += cache->Count();
1287       if (cache->IsLocked()) {
1288         ++lockedImageCount;
1289       }
1290       for (const auto& value : cache->Values()) {
1291         if (value->IsLocked()) {
1292           ++lockedSurfaceCount;
1293         }
1294       }
1295     }
1296
1297     // clang-format off
1298     // We have explicit memory reporting for the surface cache which is more
1299     // accurate than the cost metrics we report here, but these metrics are
1300     // still useful to report, since they control the cache's behavior.
1301     MOZ_COLLECT_REPORT(
1302       "explicit/images/cache/overhead", KIND_HEAP, UNITS_BYTES,
1303       ShallowSizeOfIncludingThis(SurfaceCacheMallocSizeOf, lock),
1304 "Memory used by the surface cache data structures, excluding surface data.");
1305
1306     MOZ_COLLECT_REPORT(
1307       "imagelib-surface-cache-estimated-total",
1308       KIND_OTHER, UNITS_BYTES, (mMaxCost - mAvailableCost),
1309 "Estimated total memory used by the imagelib surface cache.");
1310
1311     MOZ_COLLECT_REPORT(
1312       "imagelib-surface-cache-estimated-locked",
1313       KIND_OTHER, UNITS_BYTES, mLockedCost,
1314 "Estimated memory used by locked surfaces in the imagelib surface cache.");
1315
1316     MOZ_COLLECT_REPORT(
1317       "imagelib-surface-cache-tracked-cost-count",
1318       KIND_OTHER, UNITS_COUNT, mCosts.Length(),
1319 "Total number of surfaces tracked for cost (and expiry) in the imagelib surface cache.");
1320
1321     MOZ_COLLECT_REPORT(
1322       "imagelib-surface-cache-tracked-expiry-count",
1323       KIND_OTHER, UNITS_COUNT, mExpirationTracker.Length(lock),
1324 "Total number of surfaces tracked for expiry (and cost) in the imagelib surface cache.");
1325
1326     MOZ_COLLECT_REPORT(
1327       "imagelib-surface-cache-image-count",
1328       KIND_OTHER, UNITS_COUNT, mImageCaches.Count(),
1329 "Total number of images in the imagelib surface cache.");
1330
1331     MOZ_COLLECT_REPORT(
1332       "imagelib-surface-cache-locked-image-count",
1333       KIND_OTHER, UNITS_COUNT, lockedImageCount,
1334 "Total number of locked images in the imagelib surface cache.");
1335
1336     MOZ_COLLECT_REPORT(
1337       "imagelib-surface-cache-image-surface-count",
1338       KIND_OTHER, UNITS_COUNT, totalSurfaceCount,
1339 "Total number of surfaces in the imagelib surface cache.");
1340
1341     MOZ_COLLECT_REPORT(
1342       "imagelib-surface-cache-locked-surfaces-count",
1343       KIND_OTHER, UNITS_COUNT, lockedSurfaceCount,
1344 "Total number of locked surfaces in the imagelib surface cache.");
1345
1346     MOZ_COLLECT_REPORT(
1347       "imagelib-surface-cache-overflow-count",
1348       KIND_OTHER, UNITS_COUNT, mOverflowCount,
1349 "Count of how many times the surface cache has hit its capacity and been "
1350 "unable to insert a new surface.");
1351
1352     MOZ_COLLECT_REPORT(
1353       "imagelib-surface-cache-tracking-failure-count",
1354       KIND_OTHER, UNITS_COUNT, mTrackingFailureCount,
1355 "Count of how many times the surface cache has failed to begin tracking a "
1356 "given surface.");
1357
1358     MOZ_COLLECT_REPORT(
1359       "imagelib-surface-cache-already-present-count",
1360       KIND_OTHER, UNITS_COUNT, mAlreadyPresentCount,
1361 "Count of how many times the surface cache has failed to insert a surface "
1362 "because it is already present.");
1363
1364     MOZ_COLLECT_REPORT(
1365       "imagelib-surface-cache-table-failure-count",
1366       KIND_OTHER, UNITS_COUNT, mTableFailureCount,
1367 "Count of how many times the surface cache has failed to insert a surface "
1368 "because a hash table could not accept an entry.");
1369     // clang-format on
1370
1371     return NS_OK;
1372   }
1373
1374   void CollectSizeOfSurfaces(const ImageKey aImageKey,
1375                              nsTArray<SurfaceMemoryCounter>& aCounters,
1376                              MallocSizeOf aMallocSizeOf,
1377                              const StaticMutexAutoLock& aAutoLock) {
1378     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1379     if (!cache) {
1380       return;  // No surfaces for this image.
1381     }
1382
1383     // Report all surfaces in the per-image cache.
1384     cache->CollectSizeOfSurfaces(
1385         aCounters, aMallocSizeOf,
1386         [this, &aAutoLock](NotNull<CachedSurface*> aSurface) -> void {
1387           StopTracking(aSurface, /* aIsTracked */ true, aAutoLock);
1388           // Individual surfaces must be freed outside the lock.
1389           mCachedSurfacesDiscard.AppendElement(aSurface);
1390         });
1391
1392     MaybeRemoveEmptyCache(aImageKey, cache);
1393   }
1394
1395   void ReleaseImageOnMainThread(already_AddRefed<image::Image>&& aImage,
1396                                 const StaticMutexAutoLock& aAutoLock) {
1397     RefPtr<image::Image> image = aImage;
1398     if (!image) {
1399       return;
1400     }
1401
1402     bool needsDispatch = mReleasingImagesOnMainThread.IsEmpty();
1403     mReleasingImagesOnMainThread.AppendElement(image);
1404
1405     if (!needsDispatch ||
1406         AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownFinal)) {
1407       // Either there is already a ongoing task for ClearReleasingImages() or
1408       // it's too late in shutdown to dispatch.
1409       return;
1410     }
1411
1412     NS_DispatchToMainThread(NS_NewRunnableFunction(
1413         "SurfaceCacheImpl::ReleaseImageOnMainThread",
1414         []() -> void { SurfaceCache::ClearReleasingImages(); }));
1415   }
1416
1417   void TakeReleasingImages(nsTArray<RefPtr<image::Image>>& aImage,
1418                            const StaticMutexAutoLock& aAutoLock) {
1419     MOZ_ASSERT(NS_IsMainThread());
1420     aImage.SwapElements(mReleasingImagesOnMainThread);
1421   }
1422
1423  private:
1424   already_AddRefed<ImageSurfaceCache> GetImageCache(const ImageKey aImageKey) {
1425     RefPtr<ImageSurfaceCache> imageCache;
1426     mImageCaches.Get(aImageKey, getter_AddRefs(imageCache));
1427     return imageCache.forget();
1428   }
1429
1430   void MaybeRemoveEmptyCache(const ImageKey aImageKey,
1431                              ImageSurfaceCache* aCache) {
1432     // Remove the per-image cache if it's unneeded now. Keep it if the image is
1433     // locked, since the per-image cache is where we store that state. Note that
1434     // we don't push it into mImageCachesDiscard because all of its surfaces
1435     // have been removed, so it is safe to free while holding the lock.
1436     if (aCache->IsEmpty() && !aCache->IsLocked()) {
1437       mImageCaches.Remove(aImageKey);
1438     }
1439   }
1440
1441   // This is similar to CanHold() except that it takes into account the costs of
1442   // locked surfaces. It's used internally in Insert(), but it's not exposed
1443   // publicly because we permit multithreaded access to the surface cache, which
1444   // means that the result would be meaningless: another thread could insert a
1445   // surface or lock an image at any time.
1446   bool CanHoldAfterDiscarding(const Cost aCost) const {
1447     return aCost <= mMaxCost - mLockedCost;
1448   }
1449
1450   bool MarkUsed(NotNull<CachedSurface*> aSurface,
1451                 NotNull<ImageSurfaceCache*> aCache,
1452                 const StaticMutexAutoLock& aAutoLock) {
1453     if (aCache->IsLocked()) {
1454       LockSurface(aSurface, aAutoLock);
1455       return true;
1456     }
1457
1458     nsresult rv = mExpirationTracker.MarkUsedLocked(aSurface, aAutoLock);
1459     if (NS_WARN_IF(NS_FAILED(rv))) {
1460       // If mark used fails, it is because it failed to reinsert the surface
1461       // after removing it from the tracker. Thus we need to update our
1462       // own accounting but otherwise expect it to be untracked.
1463       StopTracking(aSurface, /* aIsTracked */ false, aAutoLock);
1464       return false;
1465     }
1466     return true;
1467   }
1468
1469   void DoUnlockSurfaces(NotNull<ImageSurfaceCache*> aCache, bool aStaticOnly,
1470                         const StaticMutexAutoLock& aAutoLock) {
1471     AutoTArray<NotNull<CachedSurface*>, 8> discard;
1472
1473     // Unlock all the surfaces the per-image cache is holding.
1474     for (const auto& value : aCache->Values()) {
1475       NotNull<CachedSurface*> surface = WrapNotNull(value);
1476       if (surface->IsPlaceholder() || !surface->IsLocked()) {
1477         continue;
1478       }
1479       if (aStaticOnly &&
1480           surface->GetSurfaceKey().Playback() != PlaybackType::eStatic) {
1481         continue;
1482       }
1483       StopTracking(surface, /* aIsTracked */ true, aAutoLock);
1484       surface->SetLocked(false);
1485       if (MOZ_UNLIKELY(!StartTracking(surface, aAutoLock))) {
1486         discard.AppendElement(surface);
1487       }
1488     }
1489
1490     // Discard any that we failed to track.
1491     for (auto iter = discard.begin(); iter != discard.end(); ++iter) {
1492       Remove(*iter, /* aStopTracking */ false, aAutoLock);
1493     }
1494   }
1495
1496   void RemoveEntry(const ImageKey aImageKey, const SurfaceKey& aSurfaceKey,
1497                    const StaticMutexAutoLock& aAutoLock) {
1498     RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
1499     if (!cache) {
1500       return;  // No cached surfaces for this image.
1501     }
1502
1503     RefPtr<CachedSurface> surface =
1504         cache->Lookup(aSurfaceKey, /* aForAccess = */ false);
1505     if (!surface) {
1506       return;  // Lookup in the per-image cache missed.
1507     }
1508
1509     Remove(WrapNotNull(surface), /* aStopTracking */ true, aAutoLock);
1510   }
1511
1512   class SurfaceTracker final
1513       : public ExpirationTrackerImpl<CachedSurface, 2, StaticMutex,
1514                                      StaticMutexAutoLock> {
1515    public:
1516     explicit SurfaceTracker(uint32_t aSurfaceCacheExpirationTimeMS)
1517         : ExpirationTrackerImpl<CachedSurface, 2, StaticMutex,
1518                                 StaticMutexAutoLock>(
1519               aSurfaceCacheExpirationTimeMS, "SurfaceTracker") {}
1520
1521    protected:
1522     void NotifyExpiredLocked(CachedSurface* aSurface,
1523                              const StaticMutexAutoLock& aAutoLock) override {
1524       sInstance->Remove(WrapNotNull(aSurface), /* aStopTracking */ true,
1525                         aAutoLock);
1526     }
1527
1528     void NotifyHandlerEndLocked(const StaticMutexAutoLock& aAutoLock) override {
1529       sInstance->TakeDiscard(mDiscard, aAutoLock);
1530     }
1531
1532     void NotifyHandlerEnd() override {
1533       nsTArray<RefPtr<CachedSurface>> discard(std::move(mDiscard));
1534     }
1535
1536     StaticMutex& GetMutex() override { return sInstanceMutex; }
1537
1538     nsTArray<RefPtr<CachedSurface>> mDiscard;
1539   };
1540
1541   class MemoryPressureObserver final : public nsIObserver {
1542    public:
1543     NS_DECL_ISUPPORTS
1544
1545     NS_IMETHOD Observe(nsISupports*, const char* aTopic,
1546                        const char16_t*) override {
1547       nsTArray<RefPtr<CachedSurface>> discard;
1548       {
1549         StaticMutexAutoLock lock(sInstanceMutex);
1550         if (sInstance && strcmp(aTopic, "memory-pressure") == 0) {
1551           sInstance->DiscardForMemoryPressure(lock);
1552           sInstance->TakeDiscard(discard, lock);
1553         }
1554       }
1555       return NS_OK;
1556     }
1557
1558    private:
1559     virtual ~MemoryPressureObserver() {}
1560   };
1561
1562   nsTArray<CostEntry> mCosts;
1563   nsRefPtrHashtable<nsPtrHashKey<Image>, ImageSurfaceCache> mImageCaches;
1564   nsTArray<RefPtr<CachedSurface>> mCachedSurfacesDiscard;
1565   SurfaceTracker mExpirationTracker;
1566   RefPtr<MemoryPressureObserver> mMemoryPressureObserver;
1567   nsTArray<RefPtr<image::Image>> mReleasingImagesOnMainThread;
1568   const uint32_t mDiscardFactor;
1569   const Cost mMaxCost;
1570   Cost mAvailableCost;
1571   Cost mLockedCost;
1572   size_t mOverflowCount;
1573   size_t mAlreadyPresentCount;
1574   size_t mTableFailureCount;
1575   size_t mTrackingFailureCount;
1576 };
1577
1578 NS_IMPL_ISUPPORTS(SurfaceCacheImpl, nsIMemoryReporter)
1579 NS_IMPL_ISUPPORTS(SurfaceCacheImpl::MemoryPressureObserver, nsIObserver)
1580
1581 ///////////////////////////////////////////////////////////////////////////////
1582 // Public API
1583 ///////////////////////////////////////////////////////////////////////////////
1584
1585 /* static */
1586 void SurfaceCache::Initialize() {
1587   // Initialize preferences.
1588   MOZ_ASSERT(NS_IsMainThread());
1589   MOZ_ASSERT(!sInstance, "Shouldn't initialize more than once");
1590
1591   // See StaticPrefs for the default values of these preferences.
1592
1593   // Length of time before an unused surface is removed from the cache, in
1594   // milliseconds.
1595   uint32_t surfaceCacheExpirationTimeMS =
1596       StaticPrefs::image_mem_surfacecache_min_expiration_ms_AtStartup();
1597
1598   // What fraction of the memory used by the surface cache we should discard
1599   // when we get a memory pressure notification. This value is interpreted as
1600   // 1/N, so 1 means to discard everything, 2 means to discard about half of the
1601   // memory we're using, and so forth. We clamp it to avoid division by zero.
1602   uint32_t surfaceCacheDiscardFactor =
1603       max(StaticPrefs::image_mem_surfacecache_discard_factor_AtStartup(), 1u);
1604
1605   // Maximum size of the surface cache, in kilobytes.
1606   uint64_t surfaceCacheMaxSizeKB =
1607       StaticPrefs::image_mem_surfacecache_max_size_kb_AtStartup();
1608
1609   if (sizeof(uintptr_t) <= 4) {
1610     // Limit surface cache to 1 GB if our address space is 32 bit.
1611     surfaceCacheMaxSizeKB = 1024 * 1024;
1612   }
1613
1614   // A knob determining the actual size of the surface cache. Currently the
1615   // cache is (size of main memory) / (surface cache size factor) KB
1616   // or (surface cache max size) KB, whichever is smaller. The formula
1617   // may change in the future, though.
1618   // For example, a value of 4 would yield a 256MB cache on a 1GB machine.
1619   // The smallest machines we are likely to run this code on have 256MB
1620   // of memory, which would yield a 64MB cache on this setting.
1621   // We clamp this value to avoid division by zero.
1622   uint32_t surfaceCacheSizeFactor =
1623       max(StaticPrefs::image_mem_surfacecache_size_factor_AtStartup(), 1u);
1624
1625   // Compute the size of the surface cache.
1626   uint64_t memorySize = PR_GetPhysicalMemorySize();
1627   if (memorySize == 0) {
1628 #if !defined(__DragonFly__)
1629     MOZ_ASSERT_UNREACHABLE("PR_GetPhysicalMemorySize not implemented here");
1630 #endif
1631     memorySize = 256 * 1024 * 1024;  // Fall back to 256MB.
1632   }
1633   uint64_t proposedSize = memorySize / surfaceCacheSizeFactor;
1634   uint64_t surfaceCacheSizeBytes =
1635       min(proposedSize, surfaceCacheMaxSizeKB * 1024);
1636   uint32_t finalSurfaceCacheSizeBytes =
1637       min(surfaceCacheSizeBytes, uint64_t(UINT32_MAX));
1638
1639   // Create the surface cache singleton with the requested settings.  Note that
1640   // the size is a limit that the cache may not grow beyond, but we do not
1641   // actually allocate any storage for surfaces at this time.
1642   sInstance = new SurfaceCacheImpl(surfaceCacheExpirationTimeMS,
1643                                    surfaceCacheDiscardFactor,
1644                                    finalSurfaceCacheSizeBytes);
1645   sInstance->InitMemoryReporter();
1646 }
1647
1648 /* static */
1649 void SurfaceCache::Shutdown() {
1650   RefPtr<SurfaceCacheImpl> cache;
1651   {
1652     StaticMutexAutoLock lock(sInstanceMutex);
1653     MOZ_ASSERT(NS_IsMainThread());
1654     MOZ_ASSERT(sInstance, "No singleton - was Shutdown() called twice?");
1655     cache = sInstance.forget();
1656   }
1657 }
1658
1659 /* static */
1660 LookupResult SurfaceCache::Lookup(const ImageKey aImageKey,
1661                                   const SurfaceKey& aSurfaceKey,
1662                                   bool aMarkUsed) {
1663   nsTArray<RefPtr<CachedSurface>> discard;
1664   LookupResult rv(MatchType::NOT_FOUND);
1665
1666   {
1667     StaticMutexAutoLock lock(sInstanceMutex);
1668     if (!sInstance) {
1669       return rv;
1670     }
1671
1672     rv = sInstance->Lookup(aImageKey, aSurfaceKey, lock, aMarkUsed);
1673     sInstance->TakeDiscard(discard, lock);
1674   }
1675
1676   return rv;
1677 }
1678
1679 /* static */
1680 LookupResult SurfaceCache::LookupBestMatch(const ImageKey aImageKey,
1681                                            const SurfaceKey& aSurfaceKey,
1682                                            bool aMarkUsed) {
1683   nsTArray<RefPtr<CachedSurface>> discard;
1684   LookupResult rv(MatchType::NOT_FOUND);
1685
1686   {
1687     StaticMutexAutoLock lock(sInstanceMutex);
1688     if (!sInstance) {
1689       return rv;
1690     }
1691
1692     rv = sInstance->LookupBestMatch(aImageKey, aSurfaceKey, lock, aMarkUsed);
1693     sInstance->TakeDiscard(discard, lock);
1694   }
1695
1696   return rv;
1697 }
1698
1699 /* static */
1700 InsertOutcome SurfaceCache::Insert(NotNull<ISurfaceProvider*> aProvider) {
1701   nsTArray<RefPtr<CachedSurface>> discard;
1702   InsertOutcome rv(InsertOutcome::FAILURE);
1703
1704   {
1705     StaticMutexAutoLock lock(sInstanceMutex);
1706     if (!sInstance) {
1707       return rv;
1708     }
1709
1710     rv = sInstance->Insert(aProvider, /* aSetAvailable = */ false, lock);
1711     sInstance->TakeDiscard(discard, lock);
1712   }
1713
1714   return rv;
1715 }
1716
1717 /* static */
1718 bool SurfaceCache::CanHold(const IntSize& aSize,
1719                            uint32_t aBytesPerPixel /* = 4 */) {
1720   StaticMutexAutoLock lock(sInstanceMutex);
1721   if (!sInstance) {
1722     return false;
1723   }
1724
1725   Cost cost = ComputeCost(aSize, aBytesPerPixel);
1726   return sInstance->CanHold(cost);
1727 }
1728
1729 /* static */
1730 bool SurfaceCache::CanHold(size_t aSize) {
1731   StaticMutexAutoLock lock(sInstanceMutex);
1732   if (!sInstance) {
1733     return false;
1734   }
1735
1736   return sInstance->CanHold(aSize);
1737 }
1738
1739 /* static */
1740 void SurfaceCache::SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider) {
1741   StaticMutexAutoLock lock(sInstanceMutex);
1742   if (!sInstance) {
1743     return;
1744   }
1745
1746   sInstance->SurfaceAvailable(aProvider, lock);
1747 }
1748
1749 /* static */
1750 void SurfaceCache::LockImage(const ImageKey aImageKey) {
1751   StaticMutexAutoLock lock(sInstanceMutex);
1752   if (sInstance) {
1753     return sInstance->LockImage(aImageKey);
1754   }
1755 }
1756
1757 /* static */
1758 void SurfaceCache::UnlockImage(const ImageKey aImageKey) {
1759   StaticMutexAutoLock lock(sInstanceMutex);
1760   if (sInstance) {
1761     return sInstance->UnlockImage(aImageKey, lock);
1762   }
1763 }
1764
1765 /* static */
1766 void SurfaceCache::UnlockEntries(const ImageKey aImageKey) {
1767   StaticMutexAutoLock lock(sInstanceMutex);
1768   if (sInstance) {
1769     return sInstance->UnlockEntries(aImageKey, lock);
1770   }
1771 }
1772
1773 /* static */
1774 void SurfaceCache::RemoveImage(const ImageKey aImageKey) {
1775   RefPtr<ImageSurfaceCache> discard;
1776   {
1777     StaticMutexAutoLock lock(sInstanceMutex);
1778     if (sInstance) {
1779       discard = sInstance->RemoveImage(aImageKey, lock);
1780     }
1781   }
1782 }
1783
1784 /* static */
1785 void SurfaceCache::PruneImage(const ImageKey aImageKey) {
1786   nsTArray<RefPtr<CachedSurface>> discard;
1787   {
1788     StaticMutexAutoLock lock(sInstanceMutex);
1789     if (sInstance) {
1790       sInstance->PruneImage(aImageKey, lock);
1791       sInstance->TakeDiscard(discard, lock);
1792     }
1793   }
1794 }
1795
1796 /* static */
1797 bool SurfaceCache::InvalidateImage(const ImageKey aImageKey) {
1798   nsTArray<RefPtr<CachedSurface>> discard;
1799   bool rv = false;
1800   {
1801     StaticMutexAutoLock lock(sInstanceMutex);
1802     if (sInstance) {
1803       rv = sInstance->InvalidateImage(aImageKey, lock);
1804       sInstance->TakeDiscard(discard, lock);
1805     }
1806   }
1807   return rv;
1808 }
1809
1810 /* static */
1811 void SurfaceCache::DiscardAll() {
1812   nsTArray<RefPtr<CachedSurface>> discard;
1813   {
1814     StaticMutexAutoLock lock(sInstanceMutex);
1815     if (sInstance) {
1816       sInstance->DiscardAll(lock);
1817       sInstance->TakeDiscard(discard, lock);
1818     }
1819   }
1820 }
1821
1822 /* static */
1823 void SurfaceCache::ResetAnimation(const ImageKey aImageKey,
1824                                   const SurfaceKey& aSurfaceKey) {
1825   RefPtr<CachedSurface> surface;
1826   nsTArray<RefPtr<CachedSurface>> discard;
1827   {
1828     StaticMutexAutoLock lock(sInstanceMutex);
1829     if (!sInstance) {
1830       return;
1831     }
1832
1833     surface =
1834         sInstance->GetSurfaceForResetAnimation(aImageKey, aSurfaceKey, lock);
1835     sInstance->TakeDiscard(discard, lock);
1836   }
1837
1838   // Calling Reset will acquire the AnimationSurfaceProvider::mFramesMutex
1839   // mutex. In other places we acquire the mFramesMutex then call into the
1840   // surface cache (acquiring the surface cache mutex), so that determines a
1841   // lock order which we must obey by calling Reset after releasing the surface
1842   // cache mutex.
1843   if (surface) {
1844     DrawableSurface drawableSurface =
1845         surface->GetDrawableSurfaceEvenIfPlaceholder();
1846     if (drawableSurface) {
1847       MOZ_ASSERT(surface->GetSurfaceKey() == aSurfaceKey,
1848                  "ResetAnimation() not returning an exact match?");
1849
1850       drawableSurface.Reset();
1851     }
1852   }
1853 }
1854
1855 /* static */
1856 void SurfaceCache::CollectSizeOfSurfaces(
1857     const ImageKey aImageKey, nsTArray<SurfaceMemoryCounter>& aCounters,
1858     MallocSizeOf aMallocSizeOf) {
1859   nsTArray<RefPtr<CachedSurface>> discard;
1860   {
1861     StaticMutexAutoLock lock(sInstanceMutex);
1862     if (!sInstance) {
1863       return;
1864     }
1865
1866     sInstance->CollectSizeOfSurfaces(aImageKey, aCounters, aMallocSizeOf, lock);
1867     sInstance->TakeDiscard(discard, lock);
1868   }
1869 }
1870
1871 /* static */
1872 size_t SurfaceCache::MaximumCapacity() {
1873   StaticMutexAutoLock lock(sInstanceMutex);
1874   if (!sInstance) {
1875     return 0;
1876   }
1877
1878   return sInstance->MaximumCapacity();
1879 }
1880
1881 /* static */
1882 bool SurfaceCache::IsLegalSize(const IntSize& aSize) {
1883   // reject over-wide or over-tall images
1884   const int32_t k64KLimit = 0x0000FFFF;
1885   if (MOZ_UNLIKELY(aSize.width > k64KLimit || aSize.height > k64KLimit)) {
1886     NS_WARNING("image too big");
1887     return false;
1888   }
1889
1890   // protect against invalid sizes
1891   if (MOZ_UNLIKELY(aSize.height <= 0 || aSize.width <= 0)) {
1892     return false;
1893   }
1894
1895   // check to make sure we don't overflow a 32-bit
1896   CheckedInt32 requiredBytes =
1897       CheckedInt32(aSize.width) * CheckedInt32(aSize.height) * 4;
1898   if (MOZ_UNLIKELY(!requiredBytes.isValid())) {
1899     NS_WARNING("width or height too large");
1900     return false;
1901   }
1902   const int32_t maxSize = StaticPrefs::image_mem_max_legal_imgframe_size_kb();
1903   if (MOZ_UNLIKELY(maxSize > 0 && requiredBytes.value() / 1024 > maxSize)) {
1904     return false;
1905   }
1906   return true;
1907 }
1908
1909 IntSize SurfaceCache::ClampVectorSize(const IntSize& aSize) {
1910   // If we exceed the maximum, we need to scale the size downwards to fit.
1911   // It shouldn't get here if it is significantly larger because
1912   // VectorImage::UseSurfaceCacheForSize should prevent us from requesting
1913   // a rasterized version of a surface greater than 4x the maximum.
1914   int32_t maxSizeKB =
1915       StaticPrefs::image_cache_max_rasterized_svg_threshold_kb();
1916   if (maxSizeKB <= 0) {
1917     return aSize;
1918   }
1919
1920   int64_t proposedKB = int64_t(aSize.width) * aSize.height / 256;
1921   if (maxSizeKB >= proposedKB) {
1922     return aSize;
1923   }
1924
1925   double scale = sqrt(double(maxSizeKB) / proposedKB);
1926   return IntSize(int32_t(scale * aSize.width), int32_t(scale * aSize.height));
1927 }
1928
1929 IntSize SurfaceCache::ClampSize(ImageKey aImageKey, const IntSize& aSize) {
1930   if (aImageKey->GetType() != imgIContainer::TYPE_VECTOR) {
1931     return aSize;
1932   }
1933
1934   return ClampVectorSize(aSize);
1935 }
1936
1937 /* static */
1938 void SurfaceCache::ReleaseImageOnMainThread(
1939     already_AddRefed<image::Image> aImage, bool aAlwaysProxy) {
1940   if (NS_IsMainThread() && !aAlwaysProxy) {
1941     RefPtr<image::Image> image = std::move(aImage);
1942     return;
1943   }
1944
1945   // Don't try to dispatch the release after shutdown, we'll just leak the
1946   // runnable.
1947   if (AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownFinal)) {
1948     return;
1949   }
1950
1951   StaticMutexAutoLock lock(sInstanceMutex);
1952   if (sInstance) {
1953     sInstance->ReleaseImageOnMainThread(std::move(aImage), lock);
1954   } else {
1955     NS_ReleaseOnMainThread("SurfaceCache::ReleaseImageOnMainThread",
1956                            std::move(aImage), /* aAlwaysProxy */ true);
1957   }
1958 }
1959
1960 /* static */
1961 void SurfaceCache::ClearReleasingImages() {
1962   MOZ_ASSERT(NS_IsMainThread());
1963
1964   nsTArray<RefPtr<image::Image>> images;
1965   {
1966     StaticMutexAutoLock lock(sInstanceMutex);
1967     if (sInstance) {
1968       sInstance->TakeReleasingImages(images, lock);
1969     }
1970   }
1971 }
1972
1973 }  // namespace image
1974 }  // namespace mozilla