Add m-esr52 at 52.6.0

1 files changed, 1164 insertions, 0 deletions

diff --git a/image/SurfaceCache.cpp b/image/SurfaceCache.cpp
new file mode 100644
index 000000000..66fdfcca0
--- /dev/null
+++ b/image/SurfaceCache.cpp
@@ -0,0 +1,1164 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * SurfaceCache is a service for caching temporary surfaces in imagelib.
+ */
+
+#include "SurfaceCache.h"
+
+#include <algorithm>
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Likely.h"
+#include "mozilla/Move.h"
+#include "mozilla/Pair.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Tuple.h"
+#include "nsIMemoryReporter.h"
+#include "gfx2DGlue.h"
+#include "gfxPlatform.h"
+#include "gfxPrefs.h"
+#include "imgFrame.h"
+#include "Image.h"
+#include "ISurfaceProvider.h"
+#include "LookupResult.h"
+#include "nsExpirationTracker.h"
+#include "nsHashKeys.h"
+#include "nsRefPtrHashtable.h"
+#include "nsSize.h"
+#include "nsTArray.h"
+#include "prsystem.h"
+#include "ShutdownTracker.h"
+
+using std::max;
+using std::min;
+
+namespace mozilla {
+
+using namespace gfx;
+
+namespace image {
+
+class CachedSurface;
+class SurfaceCacheImpl;
+
+///////////////////////////////////////////////////////////////////////////////
+// Static Data
+///////////////////////////////////////////////////////////////////////////////
+
+// The single surface cache instance.
+static StaticRefPtr<SurfaceCacheImpl> sInstance;
+
+// The mutex protecting the surface cache.
+static StaticMutex sInstanceMutex;
+
+///////////////////////////////////////////////////////////////////////////////
+// SurfaceCache Implementation
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Cost models the cost of storing a surface in the cache. Right now, this is
+ * simply an estimate of the size of the surface in bytes, but in the future it
+ * may be worth taking into account the cost of rematerializing the surface as
+ * well.
+ */
+typedef size_t Cost;
+
+static Cost
+ComputeCost(const IntSize& aSize, uint32_t aBytesPerPixel)
+{
+  MOZ_ASSERT(aBytesPerPixel == 1 || aBytesPerPixel == 4);
+  return aSize.width * aSize.height * aBytesPerPixel;
+}
+
+/**
+ * Since we want to be able to make eviction decisions based on cost, we need to
+ * be able to look up the CachedSurface which has a certain cost as well as the
+ * cost associated with a certain CachedSurface. To make this possible, in data
+ * structures we actually store a CostEntry, which contains a weak pointer to
+ * its associated surface.
+ *
+ * To make usage of the weak pointer safe, SurfaceCacheImpl always calls
+ * StartTracking after a surface is stored in the cache and StopTracking before
+ * it is removed.
+ */
+class CostEntry
+{
+public:
+  CostEntry(NotNull<CachedSurface*> aSurface, Cost aCost)
+    : mSurface(aSurface)
+    , mCost(aCost)
+  { }
+
+  NotNull<CachedSurface*> Surface() const { return mSurface; }
+  Cost GetCost() const { return mCost; }
+
+  bool operator==(const CostEntry& aOther) const
+  {
+    return mSurface == aOther.mSurface &&
+           mCost == aOther.mCost;
+  }
+
+  bool operator<(const CostEntry& aOther) const
+  {
+    return mCost < aOther.mCost ||
+           (mCost == aOther.mCost && mSurface < aOther.mSurface);
+  }
+
+private:
+  NotNull<CachedSurface*> mSurface;
+  Cost                    mCost;
+};
+
+/**
+ * A CachedSurface associates a surface with a key that uniquely identifies that
+ * surface.
+ */
+class CachedSurface
+{
+  ~CachedSurface() { }
+public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(CachedSurface)
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CachedSurface)
+
+  explicit CachedSurface(NotNull<ISurfaceProvider*> aProvider)
+    : mProvider(aProvider)
+    , mIsLocked(false)
+  { }
+
+  DrawableSurface GetDrawableSurface() const
+  {
+    if (MOZ_UNLIKELY(IsPlaceholder())) {
+      MOZ_ASSERT_UNREACHABLE("Called GetDrawableSurface() on a placeholder");
+      return DrawableSurface();
+    }
+
+    return mProvider->Surface();
+  }
+
+  void SetLocked(bool aLocked)
+  {
+    if (IsPlaceholder()) {
+      return;  // Can't lock a placeholder.
+    }
+
+    // Update both our state and our provider's state. Some surface providers
+    // are permanently locked; maintaining our own locking state enables us to
+    // respect SetLocked() even when it's meaningless from the provider's
+    // perspective.
+    mIsLocked = aLocked;
+    mProvider->SetLocked(aLocked);
+  }
+
+  bool IsLocked() const
+  {
+    return !IsPlaceholder() && mIsLocked && mProvider->IsLocked();
+  }
+
+  bool IsPlaceholder() const { return mProvider->Availability().IsPlaceholder(); }
+  bool IsDecoded() const { return !IsPlaceholder() && mProvider->IsFinished(); }
+
+  ImageKey GetImageKey() const { return mProvider->GetImageKey(); }
+  SurfaceKey GetSurfaceKey() const { return mProvider->GetSurfaceKey(); }
+  nsExpirationState* GetExpirationState() { return &mExpirationState; }
+
+  CostEntry GetCostEntry()
+  {
+    return image::CostEntry(WrapNotNull(this), mProvider->LogicalSizeInBytes());
+  }
+
+  // A helper type used by SurfaceCacheImpl::CollectSizeOfSurfaces.
+  struct MOZ_STACK_CLASS SurfaceMemoryReport
+  {
+    SurfaceMemoryReport(nsTArray<SurfaceMemoryCounter>& aCounters,
+                        MallocSizeOf                    aMallocSizeOf)
+      : mCounters(aCounters)
+      , mMallocSizeOf(aMallocSizeOf)
+    { }
+
+    void Add(NotNull<CachedSurface*> aCachedSurface)
+    {
+      SurfaceMemoryCounter counter(aCachedSurface->GetSurfaceKey(),
+                                   aCachedSurface->IsLocked());
+
+      if (aCachedSurface->IsPlaceholder()) {
+        return;
+      }
+
+      // Record the memory used by the ISurfaceProvider. This may not have a
+      // straightforward relationship to the size of the surface that
+      // DrawableRef() returns if the surface is generated dynamically. (i.e.,
+      // for surfaces with PlaybackType::eAnimated.)
+      size_t heap = 0;
+      size_t nonHeap = 0;
+      aCachedSurface->mProvider
+        ->AddSizeOfExcludingThis(mMallocSizeOf, heap, nonHeap);
+      counter.Values().SetDecodedHeap(heap);
+      counter.Values().SetDecodedNonHeap(nonHeap);
+
+      mCounters.AppendElement(counter);
+    }
+
+  private:
+    nsTArray<SurfaceMemoryCounter>& mCounters;
+    MallocSizeOf                    mMallocSizeOf;
+  };
+
+private:
+  nsExpirationState                 mExpirationState;
+  NotNull<RefPtr<ISurfaceProvider>> mProvider;
+  bool                              mIsLocked;
+};
+
+static int64_t
+AreaOfIntSize(const IntSize& aSize) {
+  return static_cast<int64_t>(aSize.width) * static_cast<int64_t>(aSize.height);
+}
+
+/**
+ * An ImageSurfaceCache is a per-image surface cache. For correctness we must be
+ * able to remove all surfaces associated with an image when the image is
+ * destroyed or invalidated. Since this will happen frequently, it makes sense
+ * to make it cheap by storing the surfaces for each image separately.
+ *
+ * ImageSurfaceCache also keeps track of whether its associated image is locked
+ * or unlocked.
+ */
+class ImageSurfaceCache
+{
+  ~ImageSurfaceCache() { }
+public:
+  ImageSurfaceCache() : mLocked(false) { }
+
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(ImageSurfaceCache)
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ImageSurfaceCache)
+
+  typedef
+    nsRefPtrHashtable<nsGenericHashKey<SurfaceKey>, CachedSurface> SurfaceTable;
+
+  bool IsEmpty() const { return mSurfaces.Count() == 0; }
+
+  void Insert(NotNull<CachedSurface*> aSurface)
+  {
+    MOZ_ASSERT(!mLocked || aSurface->IsPlaceholder() || aSurface->IsLocked(),
+               "Inserting an unlocked surface for a locked image");
+    mSurfaces.Put(aSurface->GetSurfaceKey(), aSurface);
+  }
+
+  void Remove(NotNull<CachedSurface*> aSurface)
+  {
+    MOZ_ASSERT(mSurfaces.GetWeak(aSurface->GetSurfaceKey()),
+        "Should not be removing a surface we don't have");
+
+    mSurfaces.Remove(aSurface->GetSurfaceKey());
+  }
+
+  already_AddRefed<CachedSurface> Lookup(const SurfaceKey& aSurfaceKey)
+  {
+    RefPtr<CachedSurface> surface;
+    mSurfaces.Get(aSurfaceKey, getter_AddRefs(surface));
+    return surface.forget();
+  }
+
+  Pair<already_AddRefed<CachedSurface>, MatchType>
+  LookupBestMatch(const SurfaceKey& aIdealKey)
+  {
+    // Try for an exact match first.
+    RefPtr<CachedSurface> exactMatch;
+    mSurfaces.Get(aIdealKey, getter_AddRefs(exactMatch));
+    if (exactMatch && exactMatch->IsDecoded()) {
+      return MakePair(exactMatch.forget(), MatchType::EXACT);
+    }
+
+    // There's no perfect match, so find the best match we can.
+    RefPtr<CachedSurface> bestMatch;
+    for (auto iter = ConstIter(); !iter.Done(); iter.Next()) {
+      NotNull<CachedSurface*> current = WrapNotNull(iter.UserData());
+      const SurfaceKey& currentKey = current->GetSurfaceKey();
+
+      // We never match a placeholder.
+      if (current->IsPlaceholder()) {
+        continue;
+      }
+      // Matching the playback type and SVG context is required.
+      if (currentKey.Playback() != aIdealKey.Playback() ||
+          currentKey.SVGContext() != aIdealKey.SVGContext()) {
+        continue;
+      }
+      // Matching the flags is required.
+      if (currentKey.Flags() != aIdealKey.Flags()) {
+        continue;
+      }
+      // Anything is better than nothing! (Within the constraints we just
+      // checked, of course.)
+      if (!bestMatch) {
+        bestMatch = current;
+        continue;
+      }
+
+      MOZ_ASSERT(bestMatch, "Should have a current best match");
+
+      // Always prefer completely decoded surfaces.
+      bool bestMatchIsDecoded = bestMatch->IsDecoded();
+      if (bestMatchIsDecoded && !current->IsDecoded()) {
+        continue;
+      }
+      if (!bestMatchIsDecoded && current->IsDecoded()) {
+        bestMatch = current;
+        continue;
+      }
+
+      SurfaceKey bestMatchKey = bestMatch->GetSurfaceKey();
+
+      // Compare sizes. We use an area-based heuristic here instead of computing a
+      // truly optimal answer, since it seems very unlikely to make a difference
+      // for realistic sizes.
+      int64_t idealArea = AreaOfIntSize(aIdealKey.Size());
+      int64_t currentArea = AreaOfIntSize(currentKey.Size());
+      int64_t bestMatchArea = AreaOfIntSize(bestMatchKey.Size());
+
+      // If the best match is smaller than the ideal size, prefer bigger sizes.
+      if (bestMatchArea < idealArea) {
+        if (currentArea > bestMatchArea) {
+          bestMatch = current;
+        }
+        continue;
+      }
+      // Other, prefer sizes closer to the ideal size, but still not smaller.
+      if (idealArea <= currentArea && currentArea < bestMatchArea) {
+        bestMatch = current;
+        continue;
+      }
+      // This surface isn't an improvement over the current best match.
+    }
+
+    MatchType matchType;
+    if (bestMatch) {
+      if (!exactMatch) {
+        // No exact match, but we found a substitute.
+        matchType = MatchType::SUBSTITUTE_BECAUSE_NOT_FOUND;
+      } else if (exactMatch != bestMatch) {
+        // The exact match is still decoding, but we found a substitute.
+        matchType = MatchType::SUBSTITUTE_BECAUSE_PENDING;
+      } else {
+        // The exact match is still decoding, but it's the best we've got.
+        matchType = MatchType::EXACT;
+      }
+    } else {
+      if (exactMatch) {
+        // We found an "exact match"; it must have been a placeholder.
+        MOZ_ASSERT(exactMatch->IsPlaceholder());
+        matchType = MatchType::PENDING;
+      } else {
+        // We couldn't find an exact match *or* a substitute.
+        matchType = MatchType::NOT_FOUND;
+      }
+    }
+
+    return MakePair(bestMatch.forget(), matchType);
+  }
+
+  SurfaceTable::Iterator ConstIter() const
+  {
+    return mSurfaces.ConstIter();
+  }
+
+  void SetLocked(bool aLocked) { mLocked = aLocked; }
+  bool IsLocked() const { return mLocked; }
+
+private:
+  SurfaceTable mSurfaces;
+  bool         mLocked;
+};
+
+/**
+ * SurfaceCacheImpl is responsible for determining which surfaces will be cached
+ * and managing the surface cache data structures. Rather than interact with
+ * SurfaceCacheImpl directly, client code interacts with SurfaceCache, which
+ * maintains high-level invariants and encapsulates the details of the surface
+ * cache's implementation.
+ */
+class SurfaceCacheImpl final : public nsIMemoryReporter
+{
+public:
+  NS_DECL_ISUPPORTS
+
+  SurfaceCacheImpl(uint32_t aSurfaceCacheExpirationTimeMS,
+                   uint32_t aSurfaceCacheDiscardFactor,
+                   uint32_t aSurfaceCacheSize)
+    : mExpirationTracker(aSurfaceCacheExpirationTimeMS)
+    , mMemoryPressureObserver(new MemoryPressureObserver)
+    , mDiscardFactor(aSurfaceCacheDiscardFactor)
+    , mMaxCost(aSurfaceCacheSize)
+    , mAvailableCost(aSurfaceCacheSize)
+    , mLockedCost(0)
+    , mOverflowCount(0)
+  {
+    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+    if (os) {
+      os->AddObserver(mMemoryPressureObserver, "memory-pressure", false);
+    }
+  }
+
+private:
+  virtual ~SurfaceCacheImpl()
+  {
+    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+    if (os) {
+      os->RemoveObserver(mMemoryPressureObserver, "memory-pressure");
+    }
+
+    UnregisterWeakMemoryReporter(this);
+  }
+
+public:
+  void InitMemoryReporter() { RegisterWeakMemoryReporter(this); }
+
+  InsertOutcome Insert(NotNull<ISurfaceProvider*> aProvider,
+                       bool                       aSetAvailable,
+                       const StaticMutexAutoLock& aAutoLock)
+  {
+    // If this is a duplicate surface, refuse to replace the original.
+    // XXX(seth): Calling Lookup() and then RemoveEntry() does the lookup
+    // twice. We'll make this more efficient in bug 1185137.
+    LookupResult result = Lookup(aProvider->GetImageKey(),
+                                 aProvider->GetSurfaceKey(),
+                                 aAutoLock,
+                                 /* aMarkUsed = */ false);
+    if (MOZ_UNLIKELY(result)) {
+      return InsertOutcome::FAILURE_ALREADY_PRESENT;
+    }
+
+    if (result.Type() == MatchType::PENDING) {
+      RemoveEntry(aProvider->GetImageKey(), aProvider->GetSurfaceKey(), aAutoLock);
+    }
+
+    MOZ_ASSERT(result.Type() == MatchType::NOT_FOUND ||
+               result.Type() == MatchType::PENDING,
+               "A LookupResult with no surface should be NOT_FOUND or PENDING");
+
+    // If this is bigger than we can hold after discarding everything we can,
+    // refuse to cache it.
+    Cost cost = aProvider->LogicalSizeInBytes();
+    if (MOZ_UNLIKELY(!CanHoldAfterDiscarding(cost))) {
+      mOverflowCount++;
+      return InsertOutcome::FAILURE;
+    }
+
+    // Remove elements in order of cost until we can fit this in the cache. Note
+    // that locked surfaces aren't in mCosts, so we never remove them here.
+    while (cost > mAvailableCost) {
+      MOZ_ASSERT(!mCosts.IsEmpty(),
+                 "Removed everything and it still won't fit");
+      Remove(mCosts.LastElement().Surface(), aAutoLock);
+    }
+
+    // Locate the appropriate per-image cache. If there's not an existing cache
+    // for this image, create it.
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aProvider->GetImageKey());
+    if (!cache) {
+      cache = new ImageSurfaceCache;
+      mImageCaches.Put(aProvider->GetImageKey(), cache);
+    }
+
+    // If we were asked to mark the cache entry available, do so.
+    if (aSetAvailable) {
+      aProvider->Availability().SetAvailable();
+    }
+
+    NotNull<RefPtr<CachedSurface>> surface =
+      WrapNotNull(new CachedSurface(aProvider));
+
+    // We require that locking succeed if the image is locked and we're not
+    // inserting a placeholder; the caller may need to know this to handle
+    // errors correctly.
+    if (cache->IsLocked() && !surface->IsPlaceholder()) {
+      surface->SetLocked(true);
+      if (!surface->IsLocked()) {
+        return InsertOutcome::FAILURE;
+      }
+    }
+
+    // Insert.
+    MOZ_ASSERT(cost <= mAvailableCost, "Inserting despite too large a cost");
+    cache->Insert(surface);
+    StartTracking(surface, aAutoLock);
+
+    return InsertOutcome::SUCCESS;
+  }
+
+  void Remove(NotNull<CachedSurface*> aSurface,
+              const StaticMutexAutoLock& aAutoLock)
+  {
+    ImageKey imageKey = aSurface->GetImageKey();
+
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(imageKey);
+    MOZ_ASSERT(cache, "Shouldn't try to remove a surface with no image cache");
+
+    // If the surface was not a placeholder, tell its image that we discarded it.
+    if (!aSurface->IsPlaceholder()) {
+      static_cast<Image*>(imageKey)->OnSurfaceDiscarded();
+    }
+
+    StopTracking(aSurface, aAutoLock);
+    cache->Remove(aSurface);
+
+    // Remove the per-image cache if it's unneeded now. (Keep it if the image is
+    // locked, since the per-image cache is where we store that state.)
+    if (cache->IsEmpty() && !cache->IsLocked()) {
+      mImageCaches.Remove(imageKey);
+    }
+  }
+
+  void StartTracking(NotNull<CachedSurface*> aSurface,
+                     const StaticMutexAutoLock& aAutoLock)
+  {
+    CostEntry costEntry = aSurface->GetCostEntry();
+    MOZ_ASSERT(costEntry.GetCost() <= mAvailableCost,
+               "Cost too large and the caller didn't catch it");
+
+    mAvailableCost -= costEntry.GetCost();
+
+    if (aSurface->IsLocked()) {
+      mLockedCost += costEntry.GetCost();
+      MOZ_ASSERT(mLockedCost <= mMaxCost, "Locked more than we can hold?");
+    } else {
+      mCosts.InsertElementSorted(costEntry);
+      // This may fail during XPCOM shutdown, so we need to ensure the object is
+      // tracked before calling RemoveObject in StopTracking.
+      mExpirationTracker.AddObjectLocked(aSurface, aAutoLock);
+    }
+  }
+
+  void StopTracking(NotNull<CachedSurface*> aSurface,
+                    const StaticMutexAutoLock& aAutoLock)
+  {
+    CostEntry costEntry = aSurface->GetCostEntry();
+
+    if (aSurface->IsLocked()) {
+      MOZ_ASSERT(mLockedCost >= costEntry.GetCost(), "Costs don't balance");
+      mLockedCost -= costEntry.GetCost();
+      // XXX(seth): It'd be nice to use an O(log n) lookup here. This is O(n).
+      MOZ_ASSERT(!mCosts.Contains(costEntry),
+                 "Shouldn't have a cost entry for a locked surface");
+    } else {
+      if (MOZ_LIKELY(aSurface->GetExpirationState()->IsTracked())) {
+        mExpirationTracker.RemoveObjectLocked(aSurface, aAutoLock);
+      } else {
+        // Our call to AddObject must have failed in StartTracking; most likely
+        // we're in XPCOM shutdown right now.
+        NS_ASSERTION(ShutdownTracker::ShutdownHasStarted(),
+                     "Not expiration-tracking an unlocked surface!");
+      }
+
+      DebugOnly<bool> foundInCosts = mCosts.RemoveElementSorted(costEntry);
+      MOZ_ASSERT(foundInCosts, "Lost track of costs for this surface");
+    }
+
+    mAvailableCost += costEntry.GetCost();
+    MOZ_ASSERT(mAvailableCost <= mMaxCost,
+               "More available cost than we started with");
+  }
+
+  LookupResult Lookup(const ImageKey    aImageKey,
+                      const SurfaceKey& aSurfaceKey,
+                      const StaticMutexAutoLock& aAutoLock,
+                      bool aMarkUsed = true)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      // No cached surfaces for this image.
+      return LookupResult(MatchType::NOT_FOUND);
+    }
+
+    RefPtr<CachedSurface> surface = cache->Lookup(aSurfaceKey);
+    if (!surface) {
+      // Lookup in the per-image cache missed.
+      return LookupResult(MatchType::NOT_FOUND);
+    }
+
+    if (surface->IsPlaceholder()) {
+      return LookupResult(MatchType::PENDING);
+    }
+
+    DrawableSurface drawableSurface = surface->GetDrawableSurface();
+    if (!drawableSurface) {
+      // The surface was released by the operating system. Remove the cache
+      // entry as well.
+      Remove(WrapNotNull(surface), aAutoLock);
+      return LookupResult(MatchType::NOT_FOUND);
+    }
+
+    if (aMarkUsed) {
+      MarkUsed(WrapNotNull(surface), WrapNotNull(cache), aAutoLock);
+    }
+
+    MOZ_ASSERT(surface->GetSurfaceKey() == aSurfaceKey,
+               "Lookup() not returning an exact match?");
+    return LookupResult(Move(drawableSurface), MatchType::EXACT);
+  }
+
+  LookupResult LookupBestMatch(const ImageKey         aImageKey,
+                               const SurfaceKey&      aSurfaceKey,
+                               const StaticMutexAutoLock& aAutoLock)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      // No cached surfaces for this image.
+      return LookupResult(MatchType::NOT_FOUND);
+    }
+
+    // Repeatedly look up the best match, trying again if the resulting surface
+    // has been freed by the operating system, until we can either lock a
+    // surface for drawing or there are no matching surfaces left.
+    // XXX(seth): This is O(N^2), but N is expected to be very small. If we
+    // encounter a performance problem here we can revisit this.
+
+    RefPtr<CachedSurface> surface;
+    DrawableSurface drawableSurface;
+    MatchType matchType = MatchType::NOT_FOUND;
+    while (true) {
+      Tie(surface, matchType) = cache->LookupBestMatch(aSurfaceKey);
+
+      if (!surface) {
+        return LookupResult(matchType);  // Lookup in the per-image cache missed.
+      }
+
+      drawableSurface = surface->GetDrawableSurface();
+      if (drawableSurface) {
+        break;
+      }
+
+      // The surface was released by the operating system. Remove the cache
+      // entry as well.
+      Remove(WrapNotNull(surface), aAutoLock);
+    }
+
+    MOZ_ASSERT_IF(matchType == MatchType::EXACT,
+                  surface->GetSurfaceKey() == aSurfaceKey);
+    MOZ_ASSERT_IF(matchType == MatchType::SUBSTITUTE_BECAUSE_NOT_FOUND ||
+                  matchType == MatchType::SUBSTITUTE_BECAUSE_PENDING,
+      surface->GetSurfaceKey().SVGContext() == aSurfaceKey.SVGContext() &&
+      surface->GetSurfaceKey().Playback() == aSurfaceKey.Playback() &&
+      surface->GetSurfaceKey().Flags() == aSurfaceKey.Flags());
+
+    if (matchType == MatchType::EXACT) {
+      MarkUsed(WrapNotNull(surface), WrapNotNull(cache), aAutoLock);
+    }
+
+    return LookupResult(Move(drawableSurface), matchType);
+  }
+
+  bool CanHold(const Cost aCost) const
+  {
+    return aCost <= mMaxCost;
+  }
+
+  size_t MaximumCapacity() const
+  {
+    return size_t(mMaxCost);
+  }
+
+  void SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider,
+                        const StaticMutexAutoLock& aAutoLock)
+  {
+    if (!aProvider->Availability().IsPlaceholder()) {
+      MOZ_ASSERT_UNREACHABLE("Calling SurfaceAvailable on non-placeholder");
+      return;
+    }
+
+    // Reinsert the provider, requesting that Insert() mark it available. This
+    // may or may not succeed, depending on whether some other decoder has
+    // beaten us to the punch and inserted a non-placeholder version of this
+    // surface first, but it's fine either way.
+    // XXX(seth): This could be implemented more efficiently; we should be able
+    // to just update our data structures without reinserting.
+    Insert(aProvider, /* aSetAvailable = */ true, aAutoLock);
+  }
+
+  void LockImage(const ImageKey aImageKey)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      cache = new ImageSurfaceCache;
+      mImageCaches.Put(aImageKey, cache);
+    }
+
+    cache->SetLocked(true);
+
+    // We don't relock this image's existing surfaces right away; instead, the
+    // image should arrange for Lookup() to touch them if they are still useful.
+  }
+
+  void UnlockImage(const ImageKey aImageKey, const StaticMutexAutoLock& aAutoLock)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache || !cache->IsLocked()) {
+      return;  // Already unlocked.
+    }
+
+    cache->SetLocked(false);
+    DoUnlockSurfaces(WrapNotNull(cache), aAutoLock);
+  }
+
+  void UnlockEntries(const ImageKey aImageKey, const StaticMutexAutoLock& aAutoLock)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache || !cache->IsLocked()) {
+      return;  // Already unlocked.
+    }
+
+    // (Note that we *don't* unlock the per-image cache here; that's the
+    // difference between this and UnlockImage.)
+    DoUnlockSurfaces(WrapNotNull(cache), aAutoLock);
+  }
+
+  void RemoveImage(const ImageKey aImageKey, const StaticMutexAutoLock& aAutoLock)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      return;  // No cached surfaces for this image, so nothing to do.
+    }
+
+    // Discard all of the cached surfaces for this image.
+    // XXX(seth): This is O(n^2) since for each item in the cache we are
+    // removing an element from the costs array. Since n is expected to be
+    // small, performance should be good, but if usage patterns change we should
+    // change the data structure used for mCosts.
+    for (auto iter = cache->ConstIter(); !iter.Done(); iter.Next()) {
+      StopTracking(WrapNotNull(iter.UserData()), aAutoLock);
+    }
+
+    // The per-image cache isn't needed anymore, so remove it as well.
+    // This implicitly unlocks the image if it was locked.
+    mImageCaches.Remove(aImageKey);
+  }
+
+  void DiscardAll(const StaticMutexAutoLock& aAutoLock)
+  {
+    // Remove in order of cost because mCosts is an array and the other data
+    // structures are all hash tables. Note that locked surfaces are not
+    // removed, since they aren't present in mCosts.
+    while (!mCosts.IsEmpty()) {
+      Remove(mCosts.LastElement().Surface(), aAutoLock);
+    }
+  }
+
+  void DiscardForMemoryPressure(const StaticMutexAutoLock& aAutoLock)
+  {
+    // Compute our discardable cost. Since locked surfaces aren't discardable,
+    // we exclude them.
+    const Cost discardableCost = (mMaxCost - mAvailableCost) - mLockedCost;
+    MOZ_ASSERT(discardableCost <= mMaxCost, "Discardable cost doesn't add up");
+
+    // Our target is to raise our available cost by (1 / mDiscardFactor) of our
+    // discardable cost - in other words, we want to end up with about
+    // (discardableCost / mDiscardFactor) fewer bytes stored in the surface
+    // cache after we're done.
+    const Cost targetCost = mAvailableCost + (discardableCost / mDiscardFactor);
+
+    if (targetCost > mMaxCost - mLockedCost) {
+      MOZ_ASSERT_UNREACHABLE("Target cost is more than we can discard");
+      DiscardAll(aAutoLock);
+      return;
+    }
+
+    // Discard surfaces until we've reduced our cost to our target cost.
+    while (mAvailableCost < targetCost) {
+      MOZ_ASSERT(!mCosts.IsEmpty(), "Removed everything and still not done");
+      Remove(mCosts.LastElement().Surface(), aAutoLock);
+    }
+  }
+
+  void LockSurface(NotNull<CachedSurface*> aSurface,
+                   const StaticMutexAutoLock& aAutoLock)
+  {
+    if (aSurface->IsPlaceholder() || aSurface->IsLocked()) {
+      return;
+    }
+
+    StopTracking(aSurface, aAutoLock);
+
+    // Lock the surface. This can fail.
+    aSurface->SetLocked(true);
+    StartTracking(aSurface, aAutoLock);
+  }
+
+  NS_IMETHOD
+  CollectReports(nsIHandleReportCallback* aHandleReport,
+                 nsISupports*             aData,
+                 bool                     aAnonymize) override
+  {
+    StaticMutexAutoLock lock(sInstanceMutex);
+
+    // We have explicit memory reporting for the surface cache which is more
+    // accurate than the cost metrics we report here, but these metrics are
+    // still useful to report, since they control the cache's behavior.
+    MOZ_COLLECT_REPORT(
+      "imagelib-surface-cache-estimated-total",
+      KIND_OTHER, UNITS_BYTES, (mMaxCost - mAvailableCost),
+"Estimated total memory used by the imagelib surface cache.");
+
+    MOZ_COLLECT_REPORT(
+      "imagelib-surface-cache-estimated-locked",
+      KIND_OTHER, UNITS_BYTES, mLockedCost,
+"Estimated memory used by locked surfaces in the imagelib surface cache.");
+
+    MOZ_COLLECT_REPORT(
+      "imagelib-surface-cache-overflow-count",
+      KIND_OTHER, UNITS_COUNT, mOverflowCount,
+"Count of how many times the surface cache has hit its capacity and been "
+"unable to insert a new surface.");
+
+    return NS_OK;
+  }
+
+  void CollectSizeOfSurfaces(const ImageKey                  aImageKey,
+                             nsTArray<SurfaceMemoryCounter>& aCounters,
+                             MallocSizeOf                    aMallocSizeOf)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      return;  // No surfaces for this image.
+    }
+
+    // Report all surfaces in the per-image cache.
+    CachedSurface::SurfaceMemoryReport report(aCounters, aMallocSizeOf);
+    for (auto iter = cache->ConstIter(); !iter.Done(); iter.Next()) {
+      report.Add(WrapNotNull(iter.UserData()));
+    }
+  }
+
+private:
+  already_AddRefed<ImageSurfaceCache> GetImageCache(const ImageKey aImageKey)
+  {
+    RefPtr<ImageSurfaceCache> imageCache;
+    mImageCaches.Get(aImageKey, getter_AddRefs(imageCache));
+    return imageCache.forget();
+  }
+
+  // This is similar to CanHold() except that it takes into account the costs of
+  // locked surfaces. It's used internally in Insert(), but it's not exposed
+  // publicly because we permit multithreaded access to the surface cache, which
+  // means that the result would be meaningless: another thread could insert a
+  // surface or lock an image at any time.
+  bool CanHoldAfterDiscarding(const Cost aCost) const
+  {
+    return aCost <= mMaxCost - mLockedCost;
+  }
+
+  void MarkUsed(NotNull<CachedSurface*> aSurface,
+                NotNull<ImageSurfaceCache*> aCache,
+                const StaticMutexAutoLock& aAutoLock)
+  {
+    if (aCache->IsLocked()) {
+      LockSurface(aSurface, aAutoLock);
+    } else {
+      mExpirationTracker.MarkUsedLocked(aSurface, aAutoLock);
+    }
+  }
+
+  void DoUnlockSurfaces(NotNull<ImageSurfaceCache*> aCache,
+                        const StaticMutexAutoLock& aAutoLock)
+  {
+    // Unlock all the surfaces the per-image cache is holding.
+    for (auto iter = aCache->ConstIter(); !iter.Done(); iter.Next()) {
+      NotNull<CachedSurface*> surface = WrapNotNull(iter.UserData());
+      if (surface->IsPlaceholder() || !surface->IsLocked()) {
+        continue;
+      }
+      StopTracking(surface, aAutoLock);
+      surface->SetLocked(false);
+      StartTracking(surface, aAutoLock);
+    }
+  }
+
+  void RemoveEntry(const ImageKey    aImageKey,
+                   const SurfaceKey& aSurfaceKey,
+                   const StaticMutexAutoLock& aAutoLock)
+  {
+    RefPtr<ImageSurfaceCache> cache = GetImageCache(aImageKey);
+    if (!cache) {
+      return;  // No cached surfaces for this image.
+    }
+
+    RefPtr<CachedSurface> surface = cache->Lookup(aSurfaceKey);
+    if (!surface) {
+      return;  // Lookup in the per-image cache missed.
+    }
+
+    Remove(WrapNotNull(surface), aAutoLock);
+  }
+
+  struct SurfaceTracker : public ExpirationTrackerImpl<CachedSurface, 2,
+                                                       StaticMutex,
+                                                       StaticMutexAutoLock>
+  {
+    explicit SurfaceTracker(uint32_t aSurfaceCacheExpirationTimeMS)
+      : ExpirationTrackerImpl<CachedSurface, 2,
+                              StaticMutex, StaticMutexAutoLock>(
+          aSurfaceCacheExpirationTimeMS, "SurfaceTracker")
+    { }
+
+  protected:
+    void NotifyExpiredLocked(CachedSurface* aSurface,
+                             const StaticMutexAutoLock& aAutoLock) override
+    {
+      sInstance->Remove(WrapNotNull(aSurface), aAutoLock);
+    }
+
+    StaticMutex& GetMutex() override
+    {
+      return sInstanceMutex;
+    }
+  };
+
+  struct MemoryPressureObserver : public nsIObserver
+  {
+    NS_DECL_ISUPPORTS
+
+    NS_IMETHOD Observe(nsISupports*,
+                       const char* aTopic,
+                       const char16_t*) override
+    {
+      StaticMutexAutoLock lock(sInstanceMutex);
+      if (sInstance && strcmp(aTopic, "memory-pressure") == 0) {
+        sInstance->DiscardForMemoryPressure(lock);
+      }
+      return NS_OK;
+    }
+
+  private:
+    virtual ~MemoryPressureObserver() { }
+  };
+
+  nsTArray<CostEntry>                     mCosts;
+  nsRefPtrHashtable<nsPtrHashKey<Image>,
+    ImageSurfaceCache> mImageCaches;
+  SurfaceTracker                          mExpirationTracker;
+  RefPtr<MemoryPressureObserver>        mMemoryPressureObserver;
+  const uint32_t                          mDiscardFactor;
+  const Cost                              mMaxCost;
+  Cost                                    mAvailableCost;
+  Cost                                    mLockedCost;
+  size_t                                  mOverflowCount;
+};
+
+NS_IMPL_ISUPPORTS(SurfaceCacheImpl, nsIMemoryReporter)
+NS_IMPL_ISUPPORTS(SurfaceCacheImpl::MemoryPressureObserver, nsIObserver)
+
+///////////////////////////////////////////////////////////////////////////////
+// Public API
+///////////////////////////////////////////////////////////////////////////////
+
+/* static */ void
+SurfaceCache::Initialize()
+{
+  // Initialize preferences.
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!sInstance, "Shouldn't initialize more than once");
+
+  // See gfxPrefs for the default values of these preferences.
+
+  // Length of time before an unused surface is removed from the cache, in
+  // milliseconds.
+  uint32_t surfaceCacheExpirationTimeMS =
+    gfxPrefs::ImageMemSurfaceCacheMinExpirationMS();
+
+  // What fraction of the memory used by the surface cache we should discard
+  // when we get a memory pressure notification. This value is interpreted as
+  // 1/N, so 1 means to discard everything, 2 means to discard about half of the
+  // memory we're using, and so forth. We clamp it to avoid division by zero.
+  uint32_t surfaceCacheDiscardFactor =
+    max(gfxPrefs::ImageMemSurfaceCacheDiscardFactor(), 1u);
+
+  // Maximum size of the surface cache, in kilobytes.
+  uint64_t surfaceCacheMaxSizeKB = gfxPrefs::ImageMemSurfaceCacheMaxSizeKB();
+
+  // A knob determining the actual size of the surface cache. Currently the
+  // cache is (size of main memory) / (surface cache size factor) KB
+  // or (surface cache max size) KB, whichever is smaller. The formula
+  // may change in the future, though.
+  // For example, a value of 4 would yield a 256MB cache on a 1GB machine.
+  // The smallest machines we are likely to run this code on have 256MB
+  // of memory, which would yield a 64MB cache on this setting.
+  // We clamp this value to avoid division by zero.
+  uint32_t surfaceCacheSizeFactor =
+    max(gfxPrefs::ImageMemSurfaceCacheSizeFactor(), 1u);
+
+  // Compute the size of the surface cache.
+  uint64_t memorySize = PR_GetPhysicalMemorySize();
+  if (memorySize == 0) {
+    MOZ_ASSERT_UNREACHABLE("PR_GetPhysicalMemorySize not implemented here");
+    memorySize = 256 * 1024 * 1024;  // Fall back to 256MB.
+  }
+  uint64_t proposedSize = memorySize / surfaceCacheSizeFactor;
+  uint64_t surfaceCacheSizeBytes = min(proposedSize,
+                                       surfaceCacheMaxSizeKB * 1024);
+  uint32_t finalSurfaceCacheSizeBytes =
+    min(surfaceCacheSizeBytes, uint64_t(UINT32_MAX));
+
+  // Create the surface cache singleton with the requested settings.  Note that
+  // the size is a limit that the cache may not grow beyond, but we do not
+  // actually allocate any storage for surfaces at this time.
+  sInstance = new SurfaceCacheImpl(surfaceCacheExpirationTimeMS,
+                                   surfaceCacheDiscardFactor,
+                                   finalSurfaceCacheSizeBytes);
+  sInstance->InitMemoryReporter();
+}
+
+/* static */ void
+SurfaceCache::Shutdown()
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(sInstance, "No singleton - was Shutdown() called twice?");
+  sInstance = nullptr;
+}
+
+/* static */ LookupResult
+SurfaceCache::Lookup(const ImageKey         aImageKey,
+                     const SurfaceKey&      aSurfaceKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return LookupResult(MatchType::NOT_FOUND);
+  }
+
+  return sInstance->Lookup(aImageKey, aSurfaceKey, lock);
+}
+
+/* static */ LookupResult
+SurfaceCache::LookupBestMatch(const ImageKey         aImageKey,
+                              const SurfaceKey&      aSurfaceKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return LookupResult(MatchType::NOT_FOUND);
+  }
+
+  return sInstance->LookupBestMatch(aImageKey, aSurfaceKey, lock);
+}
+
+/* static */ InsertOutcome
+SurfaceCache::Insert(NotNull<ISurfaceProvider*> aProvider)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return InsertOutcome::FAILURE;
+  }
+
+  return sInstance->Insert(aProvider, /* aSetAvailable = */ false, lock);
+}
+
+/* static */ bool
+SurfaceCache::CanHold(const IntSize& aSize, uint32_t aBytesPerPixel /* = 4 */)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return false;
+  }
+
+  Cost cost = ComputeCost(aSize, aBytesPerPixel);
+  return sInstance->CanHold(cost);
+}
+
+/* static */ bool
+SurfaceCache::CanHold(size_t aSize)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return false;
+  }
+
+  return sInstance->CanHold(aSize);
+}
+
+/* static */ void
+SurfaceCache::SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return;
+  }
+
+  sInstance->SurfaceAvailable(aProvider, lock);
+}
+
+/* static */ void
+SurfaceCache::LockImage(const ImageKey aImageKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (sInstance) {
+    return sInstance->LockImage(aImageKey);
+  }
+}
+
+/* static */ void
+SurfaceCache::UnlockImage(const ImageKey aImageKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (sInstance) {
+    return sInstance->UnlockImage(aImageKey, lock);
+  }
+}
+
+/* static */ void
+SurfaceCache::UnlockEntries(const ImageKey aImageKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (sInstance) {
+    return sInstance->UnlockEntries(aImageKey, lock);
+  }
+}
+
+/* static */ void
+SurfaceCache::RemoveImage(const ImageKey aImageKey)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (sInstance) {
+    sInstance->RemoveImage(aImageKey, lock);
+  }
+}
+
+/* static */ void
+SurfaceCache::DiscardAll()
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (sInstance) {
+    sInstance->DiscardAll(lock);
+  }
+}
+
+/* static */ void
+SurfaceCache::CollectSizeOfSurfaces(const ImageKey                  aImageKey,
+                                    nsTArray<SurfaceMemoryCounter>& aCounters,
+                                    MallocSizeOf                    aMallocSizeOf)
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return;
+  }
+
+  return sInstance->CollectSizeOfSurfaces(aImageKey, aCounters, aMallocSizeOf);
+}
+
+/* static */ size_t
+SurfaceCache::MaximumCapacity()
+{
+  StaticMutexAutoLock lock(sInstanceMutex);
+  if (!sInstance) {
+    return 0;
+  }
+
+  return sInstance->MaximumCapacity();
+}
+
+} // namespace image
+} // namespace mozilla