Issue #2073 - m-c 523950: Discard decoded frames of very large GIF animations (squashed)

Controlled by image.animated.decode-on-demand.threshold-kb, default 256MB

Includes squashed bugfixes/regressions:
 - m-c 1444537: Shutting down the decode pool should make animated decoders bail early
 - m-c 1628606: Make sure to mark the surface cache entry available before sending the frame complete notification
 - m-c 1502275: Skip recreating the decoder after redecode errors if an animated image is reset
 - m-c 1443232: Don't insert frames into our AnimationFrameBuffer that we consider in error and unusable

gfx/thebes/gfxPrefs.h

@@ -429,6 +429,8 @@ private:
 #endif
   DECL_GFX_PREF(Live, "gl.require-hardware",                   RequireHardwareGL, bool, false);
 
+  DECL_GFX_PREF(Live, "image.animated.decode-on-demand.threshold-kb", ImageAnimatedDecodeOnDemandThresholdKB, uint32_t, 256*1024);
+  DECL_GFX_PREF(Live, "image.animated.decode-on-demand.batch-size", ImageAnimatedDecodeOnDemandBatchSize, uint32_t, 6);
   DECL_GFX_PREF(Once, "image.cache.size",                      ImageCacheSize, int32_t, 5*1024*1024);
   DECL_GFX_PREF(Once, "image.cache.timeweight",                ImageCacheTimeWeight, int32_t, 500);
   DECL_GFX_PREF(Live, "image.decode-immediately.enabled",      ImageDecodeImmediatelyEnabled, bool, false);

image/AnimationFrameBuffer.cpp

@@ -0,0 +1,324 @@
+/* -*- 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/. */
+
+#include "AnimationFrameBuffer.h"
+#include "mozilla/Move.h"             // for Move
+
+namespace mozilla {
+namespace image {
+
+AnimationFrameBuffer::AnimationFrameBuffer()
+  : mThreshold(0)
+  , mBatch(0)
+  , mPending(0)
+  , mAdvance(0)
+  , mInsertIndex(0)
+  , mGetIndex(0)
+  , mSizeKnown(false)
+  , mRedecodeError(false)
+{ }
+
+void
+AnimationFrameBuffer::Initialize(size_t aThreshold,
+                                 size_t aBatch,
+                                 size_t aStartFrame)
+{
+  MOZ_ASSERT(mThreshold == 0);
+  MOZ_ASSERT(mBatch == 0);
+  MOZ_ASSERT(mPending == 0);
+  MOZ_ASSERT(mAdvance == 0);
+  MOZ_ASSERT(mFrames.IsEmpty());
+
+  mThreshold = aThreshold;
+  mBatch = aBatch;
+  mAdvance = aStartFrame;
+
+  if (mBatch > SIZE_MAX/4) {
+    // Batch size is so big, we will just end up decoding the whole animation.
+    mBatch = SIZE_MAX/4;
+  } else if (mBatch < 1) {
+    // Never permit a batch size smaller than 1. We always want to be asking for
+    // at least one frame to start.
+    mBatch = 1;
+  }
+
+  // To simplify the code, we have the assumption that the threshold for
+  // entering discard-after-display mode is at least twice the batch size (since
+  // that is the most frames-pending-decode we will request) + 1 for the current
+  // frame. That way the redecoded frames being inserted will never risk
+  // overlapping the frames we will discard due to the animation progressing.
+  // That may cause us to use a little more memory than we want but that is an
+  // acceptable tradeoff for simplicity.
+  size_t minThreshold = 2 * mBatch + 1;
+  if (mThreshold < minThreshold) {
+    mThreshold = minThreshold;
+  }
+
+  // The maximum number of frames we should ever have decoded at one time is
+  // twice the batch. That is a good as number as any to start our decoding at.
+  mPending = mBatch * 2;
+}
+
+bool
+AnimationFrameBuffer::Insert(RawAccessFrameRef&& aFrame)
+{
+  // We should only insert new frames if we actually asked for them.
+  MOZ_ASSERT(mPending > 0);
+
+  if (mSizeKnown) {
+    // We only insert after the size is known if we are repeating the animation
+    // and we did not keep all of the frames. Replace whatever is there
+    // (probably an empty frame) with the new frame.
+    MOZ_ASSERT(MayDiscard());
+
+    // The first decode produced fewer frames than the redecodes, presumably
+    // because it hit an out-of-memory error which later attempts avoided. Just
+    // stop the animation because we can't tell the image that we have more
+    // frames now.
+    if (mInsertIndex >= mFrames.Length()) {
+      mRedecodeError = true;
+      mPending = 0;
+      return false;
+    }
+
+    if (mInsertIndex > 0) {
+      MOZ_ASSERT(!mFrames[mInsertIndex]);
+      mFrames[mInsertIndex] = Move(aFrame);
+    }
+  } else if (mInsertIndex == mFrames.Length()) {
+    // We are still on the first pass of the animation decoding, so this is
+    // the first time we have seen this frame.
+    mFrames.AppendElement(Move(aFrame));
+
+    if (mInsertIndex == mThreshold) {
+      // We just tripped over the threshold for the first time. This is our
+      // chance to do any clearing of already displayed frames. After this,
+      // we only need to release as we advance or force a restart.
+      MOZ_ASSERT(MayDiscard());
+      MOZ_ASSERT(mGetIndex < mInsertIndex);
+      for (size_t i = 1; i < mGetIndex; ++i) {
+        RawAccessFrameRef discard = Move(mFrames[i]);
+      }
+    }
+  } else if (mInsertIndex > 0) {
+    // We were forced to restart an animation before we decoded the last
+    // frame. If we were discarding frames, then we tossed what we had
+    // except for the first frame.
+    MOZ_ASSERT(mInsertIndex < mFrames.Length());
+    MOZ_ASSERT(!mFrames[mInsertIndex]);
+    MOZ_ASSERT(MayDiscard());
+    mFrames[mInsertIndex] = Move(aFrame);
+  } else { // mInsertIndex == 0
+    // We were forced to restart an animation before we decoded the last
+    // frame. We don't need the redecoded first frame because we always keep
+    // the original.
+    MOZ_ASSERT(MayDiscard());
+  }
+
+  MOZ_ASSERT(mFrames[mInsertIndex]);
+  ++mInsertIndex;
+
+  // Ensure we only request more decoded frames if we actually need them. If we
+  // need to advance to a certain point in the animation on behalf of the owner,
+  // then do so. This ensures we keep decoding. If the batch size is really
+  // small (i.e. 1), it is possible advancing will request the decoder to
+  // "restart", but we haven't told it to stop yet. Note that we skip the first
+  // insert because we actually start "advanced" to the first frame anyways.
+  bool continueDecoding = --mPending > 0;
+  if (mAdvance > 0 && mInsertIndex > 1) {
+    continueDecoding |= AdvanceInternal();
+    --mAdvance;
+  }
+  return continueDecoding;
+}
+
+bool
+AnimationFrameBuffer::MarkComplete()
+{
+  // We may have stopped decoding at a different point in the animation than we
+  // did previously. That means the decoder likely hit a new error, e.g. OOM.
+  // This will prevent us from advancing as well, because we are missing the
+  // required frames to blend.
+  //
+  // XXX(aosmond): In an ideal world, we would be generating full frames, and
+  // the consumer of our data doesn't care about our internal state. It simply
+  // knows about the first frame, the current frame, and how long to display the
+  // current frame.
+  if (NS_WARN_IF(mInsertIndex != mFrames.Length())) {
+    MOZ_ASSERT(mSizeKnown);
+    mRedecodeError = true;
+    mPending = 0;
+  }
+
+  // We reached the end of the animation, the next frame we get, if we get
+  // another, will be the first frame again.
+  mInsertIndex = 0;
+
+  // Since we only request advancing when we want to resume at a certain point
+  // in the animation, we should never exceed the number of frames.
+  MOZ_ASSERT(mAdvance == 0);
+
+  if (!mSizeKnown) {
+    // We just received the last frame in the animation. Compact the frame array
+    // because we know we won't need to grow beyond here.
+    mSizeKnown = true;
+    mFrames.Compact();
+
+    if (!MayDiscard()) {
+      // If we did not meet the threshold, then we know we want to keep all of the
+      // frames. If we also hit the last frame, we don't want to ask for more.
+      mPending = 0;
+    }
+  }
+
+  return mPending > 0;
+}
+
+DrawableFrameRef
+AnimationFrameBuffer::Get(size_t aFrame)
+{
+  // We should not have asked for a frame if we never inserted.
+  if (mFrames.IsEmpty()) {
+    MOZ_ASSERT_UNREACHABLE("Calling Get() when we have no frames");
+    return DrawableFrameRef();
+  }
+
+  // If we don't have that frame, return an empty frame ref.
+  if (aFrame >= mFrames.Length()) {
+    return DrawableFrameRef();
+  }
+
+  // We've got the requested frame because we are not discarding frames. While
+  // we typically should have not run out of frames since we ask for more before
+  // we want them, it is possible the decoder is behind.
+  if (!mFrames[aFrame]) {
+    MOZ_ASSERT(MayDiscard());
+    return DrawableFrameRef();
+  }
+
+  // If we are advancing on behalf of the animation, we don't expect it to be
+  // getting any frames (besides the first) until we get the desired frame.
+  MOZ_ASSERT(aFrame == 0 || mAdvance == 0);
+  return mFrames[aFrame]->DrawableRef();
+}
+
+bool
+AnimationFrameBuffer::AdvanceTo(size_t aExpectedFrame)
+{
+  // The owner should only be advancing once it has reached the requested frame
+  // in the animation.
+  MOZ_ASSERT(mAdvance == 0);
+  bool restartDecoder = AdvanceInternal();
+  // Advancing should always be successful, as it should only happen after the
+  // owner has accessed the next (now current) frame.
+  MOZ_ASSERT(mGetIndex == aExpectedFrame);
+  return restartDecoder;
+}
+
+bool
+AnimationFrameBuffer::AdvanceInternal()
+{
+  // We should not have advanced if we never inserted.
+  if (mFrames.IsEmpty()) {
+    MOZ_ASSERT_UNREACHABLE("Calling Advance() when we have no frames");
+    return false;
+  }
+
+  // We only want to change the current frame index if we have advanced. This
+  // means either a higher frame index, or going back to the beginning.
+  size_t framesLength = mFrames.Length();
+  // We should never have advanced beyond the frame buffer.
+  MOZ_ASSERT(mGetIndex < framesLength);
+  // We should never advance if the current frame is null -- it needs to know
+  // the timeout from it at least to know when to advance.
+  MOZ_ASSERT(mFrames[mGetIndex]);
+  if (++mGetIndex == framesLength) {
+    MOZ_ASSERT(mSizeKnown);
+    mGetIndex = 0;
+  }
+  // The owner should have already accessed the next frame, so it should also
+  // be available.
+  MOZ_ASSERT(mFrames[mGetIndex]);
+
+  // If we moved forward, that means we can remove the previous frame, assuming
+  // that frame is not the first frame. If we looped and are back at the first
+  // frame, we can remove the last frame.
+  if (MayDiscard()) {
+    RawAccessFrameRef discard;
+    if (mGetIndex > 1) {
+      discard = Move(mFrames[mGetIndex - 1]);
+    } else if (mGetIndex == 0) {
+      MOZ_ASSERT(mSizeKnown && framesLength > 1);
+      discard = Move(mFrames[framesLength - 1]);
+    }
+  }
+
+  if (!mRedecodeError && (!mSizeKnown || MayDiscard())) {
+    // Calculate how many frames we have requested ahead of the current frame.
+    size_t buffered = mPending;
+    if (mGetIndex > mInsertIndex) {
+      // It wrapped around and we are decoding the beginning again before the
+      // the display has finished the loop.
+      MOZ_ASSERT(mSizeKnown);
+      buffered += mInsertIndex + framesLength - mGetIndex - 1;
+    } else {
+      buffered += mInsertIndex - mGetIndex - 1;
+    }
+
+    if (buffered < mBatch) {
+      // If we have fewer frames than the batch size, then ask for more. If we
+      // do not have any pending, then we know that there is no active decoding.
+      mPending += mBatch;
+      return mPending == mBatch;
+    }
+  }
+
+  return false;
+}
+
+bool
+AnimationFrameBuffer::Reset()
+{
+  // The animation needs to start back at the beginning.
+  mGetIndex = 0;
+  mAdvance = 0;
+
+  if (!MayDiscard()) {
+    // If we haven't crossed the threshold, then we know by definition we have
+    // not discarded any frames. If we previously requested more frames, but
+    // it would have been more than we would have buffered otherwise, we can
+    // stop the decoding after one more frame.
+    if (mPending > 1 && mInsertIndex - 1 >= mBatch * 2) {
+      MOZ_ASSERT(!mSizeKnown);
+      mPending = 1;
+    }
+
+    // Either the decoder is still running, or we have enough frames already.
+    // No need for us to restart it.
+    return false;
+  }
+
+  // Discard all frames besides the first, because the decoder always expects
+  // that when it re-inserts a frame, it is not present. (It doesn't re-insert
+  // the first frame.)
+  for (size_t i = 1; i < mFrames.Length(); ++i) {
+    RawAccessFrameRef discard = Move(mFrames[i]);
+  }
+
+  mInsertIndex = 0;
+
+  // If we hit an error after redecoding, we never want to restart decoding.
+  if (mRedecodeError) {
+    MOZ_ASSERT(mPending == 0);
+    return false;
+  }
+
+  bool restartDecoder = mPending == 0;
+  mPending = 2 * mBatch;
+  return restartDecoder;
+}
+
+} // namespace image
+} // namespace mozilla

image/AnimationFrameBuffer.h

@@ -0,0 +1,204 @@
+/* -*- 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/. */
+
+#ifndef mozilla_image_AnimationFrameBuffer_h
+#define mozilla_image_AnimationFrameBuffer_h
+
+#include "ISurfaceProvider.h"
+
+namespace mozilla {
+namespace image {
+
+/**
+ * An AnimationFrameBuffer owns the frames outputted by an animated image
+ * decoder as well as directing its owner on how to drive the decoder,
+ * whether to produce more or to stop.
+ *
+ * Based upon its given configuration parameters, it will retain up to a
+ * certain number of frames in the buffer before deciding to discard previous
+ * frames, and relying upon the decoder to recreate older frames when the
+ * animation loops. It will also request that the decoder stop producing more
+ * frames when the display of the frames are far behind -- this allows other
+ * tasks and images which require decoding to take execution priority.
+ *
+ * The desire is that smaller animated images should be kept completely in
+ * memory while larger animated images should only keep a certain number of
+ * frames to minimize our memory footprint at the cost of CPU.
+ */
+class AnimationFrameBuffer final
+{
+public:
+  AnimationFrameBuffer();
+
+  /**
+   * Configure the frame buffer with a particular threshold and batch size. Note
+   * that the frame buffer may adjust the given values.
+   *
+   * @param aThreshold  Maximum number of frames that may be stored in the frame
+   *                    buffer before it may discard already displayed frames.
+   *                    Once exceeded, it will discard the previous frame to the
+   *                    current frame whenever Advance is called. It always
+   *                    retains the first frame.
+   *
+   * @param aBatch      Number of frames we request to be decoded each time it
+   *                    decides we need more.
+   *
+   * @param aStartFrame The starting frame for the animation. The frame buffer
+   *                    will auto-advance (and thus keep the decoding pipeline
+   *                    going) until it has reached this frame. Useful when the
+   *                    animation was progressing, but the surface was
+   *                    discarded, and we had to redecode.
+   */
+  void Initialize(size_t aThreshold, size_t aBatch, size_t aStartFrame);
+
+  /**
+   * Access a specific frame from the frame buffer. It should generally access
+   * frames in sequential order, increasing in tandem with AdvanceTo calls. The
+   * first frame may be accessed at any time. The access order should start with
+   * the same value as that given in Initialize (aStartFrame).
+   *
+   * @param aFrame      The frame index to access.
+   *
+   * @returns The frame, if available.
+   */
+  DrawableFrameRef Get(size_t aFrame);
+
+  /**
+   * Inserts a frame into the frame buffer. If it has yet to fully decode the
+   * animated image yet, then it will append the frame to its internal buffer.
+   * If it has been fully decoded, it will replace the next frame in its buffer
+   * with the given frame.
+   *
+   * Once we have a sufficient number of frames buffered relative to the
+   * currently displayed frame, it will return false to indicate the caller
+   * should stop decoding.
+   *
+   * @param aFrame      The frame to insert into the buffer.
+   *
+   * @returns True if the decoder should decode another frame.
+   */
+  bool Insert(RawAccessFrameRef&& aFrame);
+
+  /**
+   * This should be called after the last frame has been inserted. If the buffer
+   * is discarding old frames, it may request more frames to be decoded. In this
+   * case that means the decoder should start again from the beginning. This
+   * return value should be used in preference to that of the Insert call.
+   *
+   * @returns True if the decoder should decode another frame.
+   */
+  bool MarkComplete();
+
+  /**
+   * Advance the currently displayed frame of the frame buffer. If it reaches
+   * the end, it will loop back to the beginning. It should not be called unless
+   * a call to Get has returned a valid frame for the next frame index.
+   *
+   * As we advance, the number of frames we have buffered ahead of the current
+   * will shrink. Once that becomes too few, we will request a batch-sized set
+   * of frames to be decoded from the decoder.
+   *
+   * @param aExpectedFrame  The frame we expect to have advanced to. This is
+   *                        used for confirmation purposes (e.g. asserts).
+   *
+   * @returns True if the caller should restart the decoder.
+   */
+  bool AdvanceTo(size_t aExpectedFrame);
+
+  /**
+   * Resets the currently displayed frame of the frame buffer to the beginning.
+   * If the buffer is discarding old frames, it will actually discard all frames
+   * besides the first.
+   *
+   * @returns True if the caller should restart the decoder.
+   */
+  bool Reset();
+
+  /**
+   * @returns True if frames post-advance may be discarded and redecoded on
+   *          demand, else false.
+   */
+  bool MayDiscard() const { return mFrames.Length() > mThreshold; }
+
+  /**
+   * @returns True if the frame buffer was ever marked as complete. This implies
+   *          that the total number of frames is known and may be gotten from
+   *          Frames().Length().
+   */
+  bool SizeKnown() const { return mSizeKnown; }
+
+  /**
+   * @returns True if encountered an error during redecode which should cause
+   *          the caller to stop inserting frames.
+   */
+  bool HasRedecodeError() const { return mRedecodeError; }
+
+  /**
+   * @returns The current frame index we have advanced to.
+   */
+  size_t Displayed() const { return mGetIndex; }
+
+  /**
+   * @returns Outstanding frames desired from the decoder.
+   */
+  size_t PendingDecode() const { return mPending; }
+
+  /**
+   * @returns Outstanding frames to advance internally.
+   */
+  size_t PendingAdvance() const { return mAdvance; }
+
+  /**
+   * @returns Number of frames we request to be decoded each time it decides we
+   *          need more.
+   */
+  size_t Batch() const { return mBatch; }
+
+  /**
+   * @returns Maximum number of frames before we start discarding previous
+   *          frames post-advance.
+   */
+  size_t Threshold() const { return mThreshold; }
+
+  /**
+   * @returns The frames of this animation, in order. May contain empty indices.
+   */
+  const nsTArray<RawAccessFrameRef>& Frames() const { return mFrames; }
+
+private:
+  bool AdvanceInternal();
+
+  /// The frames of this animation, in order, but may have holes if discarding.
+  nsTArray<RawAccessFrameRef> mFrames;
+
+  // The maximum number of frames we can have before discarding.
+  size_t mThreshold;
+
+  // The minimum number of frames that we want buffered ahead of the display.
+  size_t mBatch;
+
+  // The number of frames to decode before we stop.
+  size_t mPending;
+
+  // The number of frames we need to auto-advance to synchronize with the caller.
+  size_t mAdvance;
+
+  // The mFrames index in which to insert the next decoded frame.
+  size_t mInsertIndex;
+
+  // The mFrames index that we have advanced to.
+  size_t mGetIndex;
+
+  // True if the total number of frames is known.
+  bool mSizeKnown;
+
+  // True if we encountered an error while redecoding.
+  bool mRedecodeError;
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_AnimationFrameBuffer_h

image/AnimationSurfaceProvider.cpp

@@ -8,6 +8,7 @@
 #include "gfxPrefs.h"
 #include "nsProxyRelease.h"
 
+#include "DecodePool.h"
 #include "Decoder.h"
 
 using namespace mozilla::gfx;
@@ -17,7 +18,8 @@ namespace image {
 
 AnimationSurfaceProvider::AnimationSurfaceProvider(NotNull<RasterImage*> aImage,
                                                    const SurfaceKey& aSurfaceKey,
-                                                   NotNull<Decoder*> aDecoder)
+                                                   NotNull<Decoder*> aDecoder,
+                                                   size_t aCurrentFrame)
   : ISurfaceProvider(ImageKey(aImage.get()), aSurfaceKey,
                      AvailabilityState::StartAsPlaceholder())
   , mImage(aImage.get())
@@ -29,6 +31,22 @@ AnimationSurfaceProvider::AnimationSurfaceProvider(NotNull<RasterImage*> aImage,
              "Use MetadataDecodingTask for metadata decodes");
   MOZ_ASSERT(!mDecoder->IsFirstFrameDecode(),
              "Use DecodedSurfaceProvider for single-frame image decodes");
+
+  // We still produce paletted surfaces for GIF which means the frames are
+  // smaller than one would expect for APNG. This may be removed if/when
+  // bug 1337111 lands and it is enabled by default.
+  size_t pixelSize = aDecoder->GetType() == DecoderType::GIF
+                     ? sizeof(uint8_t) : sizeof(uint32_t);
+
+  // Calculate how many frames we need to decode in this animation before we
+  // enter decode-on-demand mode.
+  IntSize frameSize = aSurfaceKey.Size();
+  size_t threshold =
+    (size_t(gfxPrefs::ImageAnimatedDecodeOnDemandThresholdKB()) * 1024) /
+    (pixelSize * frameSize.width * frameSize.height);
+  size_t batch = gfxPrefs::ImageAnimatedDecodeOnDemandBatchSize();
+
+  mFrames.Initialize(threshold, batch, aCurrentFrame);
 }
 
 AnimationSurfaceProvider::~AnimationSurfaceProvider()
@@ -53,6 +71,75 @@ AnimationSurfaceProvider::DropImageReference()
   NS_ReleaseOnMainThread(image.forget(), /* aAlwaysProxy = */ true);
 }
 
+void
+AnimationSurfaceProvider::Reset()
+{
+  // We want to go back to the beginning.
+  bool mayDiscard;
+  bool restartDecoder = false;
+
+  {
+    MutexAutoLock lock(mFramesMutex);
+
+    // If we have not crossed the threshold, we know we haven't discarded any
+    // frames, and thus we know it is safe move our display index back to the
+    // very beginning. It would be cleaner to let the frame buffer make this
+    // decision inside the AnimationFrameBuffer::Reset method, but if we have
+    // crossed the threshold, we need to hold onto the decoding mutex too. We
+    // should avoid blocking the main thread on the decoder threads.
+    mayDiscard = mFrames.MayDiscard();
+    if (!mayDiscard) {
+      restartDecoder = mFrames.Reset();
+    }
+  }
+
+  if (mayDiscard) {
+    // We are over the threshold and have started discarding old frames. In
+    // that case we need to seize the decoding mutex. Thankfully we know that
+    // we are in the process of decoding at most the batch size frames, so
+    // this should not take too long to acquire.
+    MutexAutoLock lock(mDecodingMutex);
+
+    // We may have hit an error while redecoding. Because FrameAnimator is
+    // tightly coupled to our own state, that means we would need to go through
+    // some heroics to resume animating in those cases. The typical reason for
+    // a redecode to fail is out of memory, and recycling should prevent most of
+    // those errors. When image.animated.generate-full-frames has shipped
+    // enabled on a release or two, we can simply remove the old FrameAnimator
+    // blending code and simplify this quite a bit -- just always pop the next
+    // full frame and timeout off the stack.
+    if (mDecoder) {
+      mDecoder = DecoderFactory::CloneAnimationDecoder(mDecoder);
+      MOZ_ASSERT(mDecoder);
+
+      MutexAutoLock lock2(mFramesMutex);
+      restartDecoder = mFrames.Reset();
+    } else {
+      MOZ_ASSERT(mFrames.HasRedecodeError());
+    }
+  }
+
+  if (restartDecoder) {
+    DecodePool::Singleton()->AsyncRun(this);
+  }
+}
+
+void
+AnimationSurfaceProvider::Advance(size_t aFrame)
+{
+  bool restartDecoder;
+
+  {
+    // Typical advancement of a frame.
+    MutexAutoLock lock(mFramesMutex);
+    restartDecoder = mFrames.AdvanceTo(aFrame);
+  }
+
+  if (restartDecoder) {
+    DecodePool::Singleton()->AsyncRun(this);
+  }
+}
+
 DrawableFrameRef
 AnimationSurfaceProvider::DrawableRef(size_t aFrame)
 {
@@ -63,19 +150,7 @@ AnimationSurfaceProvider::DrawableRef(size_t aFrame)
     return DrawableFrameRef();
   }
 
-  if (mFrames.IsEmpty()) {
+  return mFrames.Get(aFrame);
-    MOZ_ASSERT_UNREACHABLE("Calling DrawableRef() when we have no frames");
-    return DrawableFrameRef();
-  }
-
-  // If we don't have that frame, return an empty frame ref.
-  if (aFrame >= mFrames.Length()) {
-    return DrawableFrameRef();
-  }
-
-  // We've got the requested frame. Return it.
-  MOZ_ASSERT(mFrames[aFrame]);
-  return mFrames[aFrame]->DrawableRef();
 }
 
 bool
@@ -88,13 +163,20 @@ AnimationSurfaceProvider::IsFinished() const
     return false;
   }
 
-  if (mFrames.IsEmpty()) {
+  if (mFrames.Frames().IsEmpty()) {
     MOZ_ASSERT_UNREACHABLE("Calling IsFinished() when we have no frames");
     return false;
   }
 
   // As long as we have at least one finished frame, we're finished.
-  return mFrames[0]->IsFinished();
+  return mFrames.Frames()[0]->IsFinished();
+}
+
+bool
+AnimationSurfaceProvider::IsFullyDecoded() const
+{
+  MutexAutoLock lock(mFramesMutex);
+  return mFrames.SizeKnown() && !mFrames.MayDiscard();
 }
 
 size_t
@@ -125,17 +207,19 @@ AnimationSurfaceProvider::AddSizeOfExcludingThis(MallocSizeOf aMallocSizeOf,
   // that we must be careful to always use the same ordering elsewhere.
   MutexAutoLock lock(mFramesMutex);
 
-  for (const RawAccessFrameRef& frame : mFrames) {
+  for (const RawAccessFrameRef& frame : mFrames.Frames()) {
+    if (frame) {
       frame->AddSizeOfExcludingThis(aMallocSizeOf, aHeapSizeOut, aNonHeapSizeOut);
     }
   }
+}
 
 void
 AnimationSurfaceProvider::Run()
 {
   MutexAutoLock lock(mDecodingMutex);
 
-  if (!mDecoder || !mImage) {
+  if (!mDecoder) {
     MOZ_ASSERT_UNREACHABLE("Running after decoding finished?");
     return;
   }
@@ -150,15 +234,34 @@ AnimationSurfaceProvider::Run()
       // Since we're not sure, rather than call CheckForNewFrameAtYield() here
       // we call CheckForNewFrameAtTerminalState(), which handles both of these
       // possibilities.
-      CheckForNewFrameAtTerminalState();
+      bool continueDecoding = CheckForNewFrameAtTerminalState();
-
-      // We're done!
       FinishDecoding();
+
+      // Even if it is the last frame, we may not have enough frames buffered
+      // ahead of the current. If we are shutting down, we want to ensure we
+      // release the thread as soon as possible. The animation may advance even
+      // during shutdown, which keeps us decoding, and thus blocking the decode
+      // pool during teardown.
+      if (!mDecoder || !continueDecoding ||
+          DecodePool::Singleton()->IsShuttingDown()) {
         return;
       }
+      // Restart from the very beginning because the decoder was recreated.
+      continue;
+    }
+
+    // If there is output available we want to change the entry in the surface
+    // cache from a placeholder to an actual surface now before NotifyProgress
+    // call below so that when consumers get the frame complete notification
+    // from the NotifyProgress they can actually get a surface from the surface
+    // cache.
+    bool checkForNewFrameAtYieldResult = false;
+    if (result == LexerResult(Yield::OUTPUT_AVAILABLE)) {
+      checkForNewFrameAtYieldResult = CheckForNewFrameAtYield();
+    }
 
     // Notify for the progress we've made so far.
-    if (mDecoder->HasProgress()) {
+    if (mImage && mDecoder->HasProgress()) {
       NotifyProgress(WrapNotNull(mImage), WrapNotNull(mDecoder));
     }
 
@@ -168,38 +271,52 @@ AnimationSurfaceProvider::Run()
       return;
     }
 
-    // There's new output available - a new frame! Grab it.
+    // There's new output available - a new frame! Grab it. If we don't need any
+    // more for the moment we can break out of the loop. If we are shutting
+    // down, we want to ensure we release the thread as soon as possible. The
+    // animation may advance even during shutdown, which keeps us decoding, and
+    // thus blocking the decode pool during teardown.
     MOZ_ASSERT(result == LexerResult(Yield::OUTPUT_AVAILABLE));
-    CheckForNewFrameAtYield();
+    if (!checkForNewFrameAtYieldResult ||
+        DecodePool::Singleton()->IsShuttingDown()) {
+      return;
+    }
   }
 }
 
-void
+bool
 AnimationSurfaceProvider::CheckForNewFrameAtYield()
 {
   mDecodingMutex.AssertCurrentThreadOwns();
   MOZ_ASSERT(mDecoder);
 
   bool justGotFirstFrame = false;
+  bool continueDecoding;
 
   {
     MutexAutoLock lock(mFramesMutex);
 
     // Try to get the new frame from the decoder.
     RawAccessFrameRef frame = mDecoder->GetCurrentFrameRef();
+    MOZ_ASSERT(mDecoder->HasFrameToTake());
+    mDecoder->ClearHasFrameToTake();
+
     if (!frame) {
       MOZ_ASSERT_UNREACHABLE("Decoder yielded but didn't produce a frame?");
-      return;
+      return true;
     }
 
     // We should've gotten a different frame than last time.
-    MOZ_ASSERT_IF(!mFrames.IsEmpty(),
+    MOZ_ASSERT_IF(!mFrames.Frames().IsEmpty(),
-                  mFrames.LastElement().get() != frame.get());
+                  mFrames.Frames().LastElement().get() != frame.get());
 
     // Append the new frame to the list.
-    mFrames.AppendElement(Move(frame));
+    continueDecoding = mFrames.Insert(Move(frame));
 
-    if (mFrames.Length() == 1) {
+    // We only want to handle the first frame if it is the first pass for the
+    // animation decoder. The owning image will be cleared after that.
+    size_t frameCount = mFrames.Frames().Length();
+    if (frameCount == 1 && mImage) {
       justGotFirstFrame = true;
     }
   }
@@ -207,32 +324,49 @@ AnimationSurfaceProvider::CheckForNewFrameAtYield()
   if (justGotFirstFrame) {
     AnnounceSurfaceAvailable();
   }
+
+  return continueDecoding;
 }
 
-void
+bool
 AnimationSurfaceProvider::CheckForNewFrameAtTerminalState()
 {
   mDecodingMutex.AssertCurrentThreadOwns();
   MOZ_ASSERT(mDecoder);
 
   bool justGotFirstFrame = false;
+  bool continueDecoding;
 
   {
     MutexAutoLock lock(mFramesMutex);
 
+    // The decoder may or may not have a new frame for us at this point. Avoid
+    // reinserting the same frame again.
     RawAccessFrameRef frame = mDecoder->GetCurrentFrameRef();
-    if (!frame) {
+
-      return;
+    // If the decoder didn't finish a new frame (ie if, after starting the
+    // frame, it got an error and aborted the frame and the rest of the decode)
+    // that means it won't be reporting it to the image or FrameAnimator so we
+    // should ignore it too, that's what HasFrameToTake tracks basically.
+    if (!mDecoder->HasFrameToTake()) {
+      frame = RawAccessFrameRef();
+    } else {
+      MOZ_ASSERT(frame);
+      mDecoder->ClearHasFrameToTake();
     }
 
-    if (!mFrames.IsEmpty() && mFrames.LastElement().get() == frame.get()) {
+    if (!frame || (!mFrames.Frames().IsEmpty() &&
-      return;  // We already have this one.
+                   mFrames.Frames().LastElement().get() == frame.get())) {
+      return mFrames.MarkComplete();
     }
 
     // Append the new frame to the list.
-    mFrames.AppendElement(Move(frame));
+    mFrames.Insert(Move(frame));
+    continueDecoding = mFrames.MarkComplete();
 
-    if (mFrames.Length() == 1) {
+    // We only want to handle the first frame if it is the first pass for the
+    // animation decoder. The owning image will be cleared after that.
+    if (mFrames.Frames().Length() == 1 && mImage) {
       justGotFirstFrame = true;
     }
   }
@@ -240,6 +374,8 @@ AnimationSurfaceProvider::CheckForNewFrameAtTerminalState()
   if (justGotFirstFrame) {
     AnnounceSurfaceAvailable();
   }
+
+  return continueDecoding;
 }
 
 void
@@ -260,14 +396,27 @@ void
 AnimationSurfaceProvider::FinishDecoding()
 {
   mDecodingMutex.AssertCurrentThreadOwns();
-  MOZ_ASSERT(mImage);
   MOZ_ASSERT(mDecoder);
 
+  if (mImage) {
     // Send notifications.
     NotifyDecodeComplete(WrapNotNull(mImage), WrapNotNull(mDecoder));
+  }
 
-  // Destroy our decoder; we don't need it anymore.
+  // Determine if we need to recreate the decoder, in case we are discarding
+  // frames and need to loop back to the beginning.
+  bool recreateDecoder;
+  {
+    MutexAutoLock lock(mFramesMutex);
+    recreateDecoder = !mFrames.HasRedecodeError() && mFrames.MayDiscard();
+  }
+
+  if (recreateDecoder) {
+    mDecoder = DecoderFactory::CloneAnimationDecoder(mDecoder);
+    MOZ_ASSERT(mDecoder);
+  } else {
     mDecoder = nullptr;
+  }
 
   // We don't need a reference to our image anymore, either, and we don't want
   // one. We may be stored in the surface cache for a long time after decoding

image/AnimationSurfaceProvider.h

@@ -13,6 +13,7 @@
 #include "FrameAnimator.h"
 #include "IDecodingTask.h"
 #include "ISurfaceProvider.h"
+#include "AnimationFrameBuffer.h"
 
 namespace mozilla {
 namespace image {
@@ -31,7 +32,8 @@ public:
 
   AnimationSurfaceProvider(NotNull<RasterImage*> aImage,
                            const SurfaceKey& aSurfaceKey,
-                           NotNull<Decoder*> aDecoder);
+                           NotNull<Decoder*> aDecoder,
+                           size_t aCurrentFrame);
 
 
   //////////////////////////////////////////////////////////////////////////////
@@ -44,10 +46,13 @@ public:
   DrawableSurface Surface() override { return DrawableSurface(WrapNotNull(this)); }
 
   bool IsFinished() const override;
+  bool IsFullyDecoded() const override;
   size_t LogicalSizeInBytes() const override;
   void AddSizeOfExcludingThis(MallocSizeOf aMallocSizeOf,
                               size_t& aHeapSizeOut,
                               size_t& aNonHeapSizeOut) override;
+  void Reset() override;
+  void Advance(size_t aFrame) override;
 
 protected:
   DrawableFrameRef DrawableRef(size_t aFrame) override;
@@ -77,11 +82,15 @@ private:
   virtual ~AnimationSurfaceProvider();
 
   void DropImageReference();
-  void CheckForNewFrameAtYield();
-  void CheckForNewFrameAtTerminalState();
   void AnnounceSurfaceAvailable();
   void FinishDecoding();
 
+  // @returns Whether or not we should continue decoding.
+  bool CheckForNewFrameAtYield();
+
+  // @returns Whether or not we should restart decoding.
+  bool CheckForNewFrameAtTerminalState();
+
   /// The image associated with our decoder.
   RefPtr<RasterImage> mImage;
 
@@ -95,7 +104,7 @@ private:
   mutable Mutex mFramesMutex;
 
   /// The frames of this animation, in order.
-  nsTArray<RawAccessFrameRef> mFrames;
+  AnimationFrameBuffer mFrames;
 };
 
 } // namespace image

image/DecodePool.cpp

@@ -87,6 +87,12 @@ public:
     mMonitor.NotifyAll();
   }
 
+  bool IsShuttingDown() const
+  {
+    MonitorAutoLock lock(mMonitor);
+    return mShuttingDown;
+  }
+
   /// Pushes a new decode work item.
   void PushWork(IDecodingTask* aTask)
   {
@@ -150,7 +156,7 @@ private:
   nsThreadPoolNaming mThreadNaming;
 
   // mMonitor guards the queues and mShuttingDown.
-  Monitor mMonitor;
+  mutable Monitor mMonitor;
   nsTArray<RefPtr<IDecodingTask>> mHighPriorityQueue;
   nsTArray<RefPtr<IDecodingTask>> mLowPriorityQueue;
   bool mShuttingDown;
@@ -299,6 +305,12 @@ DecodePool::Observe(nsISupports*, const char* aTopic, const char16_t*)
   return NS_OK;
 }
 
+bool
+DecodePool::IsShuttingDown() const
+{
+  return mImpl->IsShuttingDown();
+}
+
 void
 DecodePool::AsyncRun(IDecodingTask* aTask)
 {

image/DecodePool.h

@@ -54,6 +54,10 @@ public:
   /// same as the number of decoding threads we're actually using.
   static uint32_t NumberOfCores();
 
+  /// True if the DecodePool is being shutdown. This may only be called by
+  /// threads from the pool to check if they should keep working or not.
+  bool IsShuttingDown() const;
+
   /// Ask the DecodePool to run @aTask asynchronously and return immediately.
   void AsyncRun(IDecodingTask* aTask);
 

image/Decoder.cpp

@@ -36,6 +36,7 @@ Decoder::Decoder(RasterImage* aImage)
   , mHaveExplicitOutputSize(false)
   , mInFrame(false)
   , mFinishedNewFrame(false)
+  , mHasFrameToTake(false)
   , mReachedTerminalState(false)
   , mDecodeDone(false)
   , mError(false)
@@ -254,6 +255,8 @@ Decoder::AllocateFrame(const gfx::IntSize& aOutputSize,
                                         mCurrentFrame.get());
 
   if (mCurrentFrame) {
+    mHasFrameToTake = true;
+
     // Gather the raw pointers the decoders will use.
     mCurrentFrame->GetImageData(&mImageData, &mImageDataLength);
     mCurrentFrame->GetPaletteData(&mColormap, &mColormapSize);
@@ -474,6 +477,7 @@ Decoder::PostError()
     mCurrentFrame->Abort();
     mInFrame = false;
     --mFrameCount;
+    mHasFrameToTake = false;
   }
 }
 

image/Decoder.h

@@ -200,6 +200,11 @@ public:
     mIterator.emplace(Move(aIterator));
   }
 
+  SourceBuffer* GetSourceBuffer() const
+  {
+    return mIterator->Owner();
+  }
+
   /**
    * Should this decoder send partial invalidations?
    */
@@ -244,6 +249,12 @@ public:
   /// Are we in the middle of a frame right now? Used for assertions only.
   bool InFrame() const { return mInFrame; }
 
+  /// Type of decoder.
+  virtual DecoderType GetType() const
+  {
+    return DecoderType::UNKNOWN;
+  }
+
   enum DecodeStyle {
       PROGRESSIVE, // produce intermediate frames representing the partial
                    // state of the image
@@ -339,6 +350,11 @@ public:
                          : RawAccessFrameRef();
   }
 
+  bool HasFrameToTake() const { return mHasFrameToTake; }
+  void ClearHasFrameToTake() {
+    MOZ_ASSERT(mHasFrameToTake);
+    mHasFrameToTake = false;
+  }
 
 protected:
   friend class nsICODecoder;
@@ -493,6 +509,10 @@ private:
   bool mInFrame : 1;
   bool mFinishedNewFrame : 1;  // True if PostFrameStop() has been called since
                                // the last call to TakeCompleteFrameCount().
+  // Has a new frame that AnimationSurfaceProvider can take. Unfortunately this
+  // has to be separate from mFinishedNewFrame because the png decoder yields a
+  // new frame before calling PostFrameStop().
+  bool mHasFrameToTake : 1;
   bool mReachedTerminalState : 1;
   bool mDecodeDone : 1;
   bool mError : 1;

image/DecoderFactory.cpp

@@ -181,7 +181,8 @@ DecoderFactory::CreateAnimationDecoder(DecoderType aType,
                                        NotNull<SourceBuffer*> aSourceBuffer,
                                        const IntSize& aIntrinsicSize,
                                        DecoderFlags aDecoderFlags,
-                                       SurfaceFlags aSurfaceFlags)
+                                       SurfaceFlags aSurfaceFlags,
+                                       size_t aCurrentFrame)
 {
   if (aType == DecoderType::UNKNOWN) {
     return nullptr;
@@ -213,7 +214,8 @@ DecoderFactory::CreateAnimationDecoder(DecoderType aType,
   NotNull<RefPtr<AnimationSurfaceProvider>> provider =
     WrapNotNull(new AnimationSurfaceProvider(aImage,
                                              surfaceKey,
-                                             WrapNotNull(decoder)));
+                                             WrapNotNull(decoder),
+                                             aCurrentFrame));
 
   // Attempt to insert the surface provider into the surface cache right away so
   // we won't trigger any more decoders with the same parameters.
@@ -226,6 +228,29 @@ DecoderFactory::CreateAnimationDecoder(DecoderType aType,
   return task.forget();
 }
 
+/* static */ already_AddRefed<Decoder>
+DecoderFactory::CloneAnimationDecoder(Decoder* aDecoder)
+{
+  MOZ_ASSERT(aDecoder);
+  MOZ_ASSERT(aDecoder->HasAnimation());
+
+  RefPtr<Decoder> decoder = GetDecoder(aDecoder->GetType(), nullptr,
+                                       /* aIsRedecode = */ true);
+  MOZ_ASSERT(decoder, "Should have a decoder now");
+
+  // Initialize the decoder.
+  decoder->SetMetadataDecode(false);
+  decoder->SetIterator(aDecoder->GetSourceBuffer()->Iterator());
+  decoder->SetDecoderFlags(aDecoder->GetDecoderFlags());
+  decoder->SetSurfaceFlags(aDecoder->GetSurfaceFlags());
+
+  if (NS_FAILED(decoder->Init())) {
+    return nullptr;
+  }
+
+  return decoder.forget();
+}
+
 /* static */ already_AddRefed<IDecodingTask>
 DecoderFactory::CreateMetadataDecoder(DecoderType aType,
                                       NotNull<RasterImage*> aImage,

image/DecoderFactory.h

@@ -92,6 +92,7 @@ public:
    * @param aDecoderFlags Flags specifying the behavior of this decoder.
    * @param aSurfaceFlags Flags specifying the type of output this decoder
    *                      should produce.
+   * @param aCurrentFrame The current frame the decoder should auto advance to.
    */
   static already_AddRefed<IDecodingTask>
   CreateAnimationDecoder(DecoderType aType,
@@ -99,7 +100,17 @@ public:
                          NotNull<SourceBuffer*> aSourceBuffer,
                          const gfx::IntSize& aIntrinsicSize,
                          DecoderFlags aDecoderFlags,
-                         SurfaceFlags aSurfaceFlags);
+                         SurfaceFlags aSurfaceFlags,
+                         size_t aCurrentFrame);
+
+  /**
+   * Creates and initializes a decoder for animated images, cloned from the
+   * given decoder.
+   *
+   * @param aDecoder Decoder to clone.
+   */
+  static already_AddRefed<Decoder>
+  CloneAnimationDecoder(Decoder* aDecoder);
 
   /**
    * Creates and initializes a metadata decoder of type @aType. This decoder

image/FrameAnimator.cpp

@@ -64,12 +64,7 @@ AnimationState::UpdateStateInternal(LookupResult& aResult,
     if (mHasBeenDecoded) {
       Maybe<uint32_t> frameCount = FrameCount();
       MOZ_ASSERT(frameCount.isSome());
-      aResult.Surface().Seek(*frameCount - 1);
+      mIsCurrentlyDecoded = aResult.Surface().IsFullyDecoded();
-      if (aResult.Surface() && aResult.Surface()->IsFinished()) {
-        mIsCurrentlyDecoded = true;
-      } else {
-        mIsCurrentlyDecoded = false;
-      }
     }
   }
 
@@ -286,8 +281,12 @@ FrameAnimator::AdvanceFrame(AnimationState& aState,
   // failure) we would have discarded all the old frames and may not yet have
   // the new ones.
   if (!nextFrame || !nextFrame->IsFinished()) {
-    // Uh oh, the frame we want to show is currently being decoded (partial)
+    // Uh oh, the frame we want to show is currently being decoded (partial).
-    // Wait until the next refresh driver tick and try again
+    // Similar to the above case, we could be blocked by network or decoding,
+    // and so we should advance our current time rather than risk jumping
+    // through the animation. We will wait until the next refresh driver tick
+    // and try again.
+    aState.mCurrentAnimationFrameTime = aTime;
     return ret;
   }
 
@@ -313,6 +312,7 @@ FrameAnimator::AdvanceFrame(AnimationState& aState,
       MOZ_ASSERT(currentFrameEndTime.isSome());
       aState.mCurrentAnimationFrameTime = *currentFrameEndTime;
       aState.mCurrentAnimationFrameIndex = nextFrameIndex;
+      aFrames.Advance(nextFrameIndex);
 
       return ret;
     }
@@ -343,6 +343,7 @@ FrameAnimator::AdvanceFrame(AnimationState& aState,
 
   // Set currentAnimationFrameIndex at the last possible moment
   aState.mCurrentAnimationFrameIndex = nextFrameIndex;
+  aFrames.Advance(nextFrameIndex);
 
   // If we're here, we successfully advanced the frame.
   ret.mFrameAdvanced = true;
@@ -350,6 +351,25 @@ FrameAnimator::AdvanceFrame(AnimationState& aState,
   return ret;
 }
 
+void
+FrameAnimator::ResetAnimation(AnimationState& aState)
+{
+  aState.ResetAnimation();
+
+  // Our surface provider is synchronized to our state, so we need to reset its
+  // state as well, if we still have one.
+  LookupResult result =
+    SurfaceCache::Lookup(ImageKey(mImage),
+                         RasterSurfaceKey(mSize,
+                                          DefaultSurfaceFlags(),
+                                          PlaybackType::eAnimated));
+  if (!result) {
+    return;
+  }
+
+  result.Surface().Reset();
+}
+
 RefreshResult
 FrameAnimator::RequestRefresh(AnimationState& aState,
                               const TimeStamp& aTime,

image/FrameAnimator.h

@@ -276,6 +276,12 @@ public:
     MOZ_COUNT_DTOR(FrameAnimator);
   }
 
+  /**
+   * Call when you need to re-start animating. Ensures we start from the first
+   * frame.
+   */
+  void ResetAnimation(AnimationState& aState);
+
   /**
    * Re-evaluate what frame we're supposed to be on, and do whatever blending
    * is necessary to get us to that frame.

image/ISurfaceProvider.h

@@ -54,6 +54,12 @@ public:
   /// @return true if DrawableRef() will return a completely decoded surface.
   virtual bool IsFinished() const = 0;
 
+  /// @return true if the underlying decoder is currently fully decoded. For
+  /// animated images, this means that at least every frame has been decoded
+  /// at least once. It does not guarantee that all of the frames are present,
+  /// as the surface provider has the option to discard as it deems necessary.
+  virtual bool IsFullyDecoded() const { return IsFinished(); }
+
   /// @return the number of bytes of memory this ISurfaceProvider is expected to
   /// require. Optimizations may result in lower real memory usage. Trivial
   /// overhead is ignored. Because this value is used in bookkeeping, it's
@@ -75,6 +81,9 @@ public:
     ref->AddSizeOfExcludingThis(aMallocSizeOf, aHeapSizeOut, aNonHeapSizeOut);
   }
 
+  virtual void Reset() { }
+  virtual void Advance(size_t aFrame) { }
+
   /// @return the availability state of this ISurfaceProvider, which indicates
   /// whether DrawableRef() could successfully return a surface. Should only be
   /// called from SurfaceCache code as it relies on SurfaceCache for
@@ -189,6 +198,36 @@ public:
     return mDrawableRef ? NS_OK : NS_ERROR_FAILURE;
   }
 
+  void Reset()
+  {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to reset a static DrawableSurface?");
+      return;
+    }
+
+    mProvider->Reset();
+  }
+
+  void Advance(size_t aFrame)
+  {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to advance a static DrawableSurface?");
+      return;
+    }
+
+    mProvider->Advance(aFrame);
+  }
+
+  bool IsFullyDecoded() const
+  {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to check decoding state of a static DrawableSurface?");
+      return false;
+    }
+
+    return mProvider->IsFullyDecoded();
+  }
+
   explicit operator bool() const { return mHaveSurface; }
   imgFrame* operator->() { return DrawableRef().get(); }
 

image/RasterImage.cpp

@@ -853,7 +853,8 @@ RasterImage::ResetAnimation()
   }
 
   MOZ_ASSERT(mAnimationState, "Should have AnimationState");
-  mAnimationState->ResetAnimation();
+  MOZ_ASSERT(mFrameAnimator, "Should have FrameAnimator");
+  mFrameAnimator->ResetAnimation(*mAnimationState);
 
   NotifyProgress(NoProgress, mAnimationState->FirstFrameRefreshArea());
 
@@ -1183,10 +1184,13 @@ RasterImage::Decode(const IntSize& aSize,
 
   // Create a decoder.
   RefPtr<IDecodingTask> task;
-  if (mAnimationState && aPlaybackType == PlaybackType::eAnimated) {
+  bool animated = mAnimationState && aPlaybackType == PlaybackType::eAnimated;
+  if (animated) {
+    size_t currentFrame = mAnimationState->GetCurrentAnimationFrameIndex();
     task = DecoderFactory::CreateAnimationDecoder(mDecoderType, WrapNotNull(this),
                                                   mSourceBuffer, mSize,
-                                                  decoderFlags, surfaceFlags);
+                                                  decoderFlags, surfaceFlags,
+                                                  currentFrame);
     mAnimationState->UpdateState(mAnimationFinished, this, mSize);
     // If the animation is finished we can draw right away because we just draw
     // the final frame all the time from now on. See comment in

image/SourceBuffer.h

@@ -187,6 +187,12 @@ public:
   /// @return a count of the bytes in all chunks we've advanced through.
   size_t ByteCount() const { return mByteCount; }
 
+  /// @return the source buffer which owns the iterator.
+  SourceBuffer* Owner() const {
+    MOZ_ASSERT(mOwner);
+    return mOwner;
+  }
+
 private:
   friend class SourceBuffer;
 

image/decoders/nsBMPDecoder.h

@@ -124,6 +124,8 @@ class nsBMPDecoder : public Decoder
 public:
   ~nsBMPDecoder();
 
+  DecoderType GetType() const override { return DecoderType::BMP; }
+
   /// Obtains the internal output image buffer.
   uint32_t* GetImageData() { return reinterpret_cast<uint32_t*>(mImageData); }
 

image/decoders/nsGIFDecoder2.h

@@ -24,6 +24,8 @@ class nsGIFDecoder2 : public Decoder
 public:
   ~nsGIFDecoder2();
 
+  DecoderType GetType() const override { return DecoderType::GIF; }
+
 protected:
   LexerResult DoDecode(SourceBufferIterator& aIterator,
                        IResumable* aOnResume) override;

image/decoders/nsICODecoder.h

@@ -69,6 +69,7 @@ public:
   /// @return The offset from the beginning of the ICO to the first resource.
   size_t FirstResourceOffset() const;
 
+  DecoderType GetType() const override { return DecoderType::ICO; }
   LexerResult DoDecode(SourceBufferIterator& aIterator,
                        IResumable* aOnResume) override;
   nsresult FinishInternal() override;

image/decoders/nsIconDecoder.h

@@ -37,6 +37,8 @@ class nsIconDecoder : public Decoder
 public:
   virtual ~nsIconDecoder();
 
+  DecoderType GetType() const override { return DecoderType::ICON; }
+
   LexerResult DoDecode(SourceBufferIterator& aIterator,
                        IResumable* aOnResume) override;
 

image/decoders/nsJPEGDecoder.h

@@ -52,6 +52,8 @@ class nsJPEGDecoder : public Decoder
 public:
   virtual ~nsJPEGDecoder();
 
+  DecoderType GetType() const override { return DecoderType::JPEG; }
+
   virtual void SetSampleSize(int aSampleSize) override
   {
     mSampleSize = aSampleSize;

image/decoders/nsPNGDecoder.h

@@ -25,6 +25,8 @@ public:
   /// @return true if this PNG is a valid ICO resource.
   bool IsValidICO() const;
 
+  DecoderType GetType() const override { return DecoderType::PNG; }
+
 protected:
   nsresult InitInternal() override;
   LexerResult DoDecode(SourceBufferIterator& aIterator,

image/decoders/nsWebPDecoder.h

@@ -21,6 +21,8 @@ class nsWebPDecoder final : public Decoder
 public:
   virtual ~nsWebPDecoder();
 
+  DecoderType GetType() const override { return DecoderType::WEBP; }
+
 protected:
   LexerResult DoDecode(SourceBufferIterator& aIterator,
                        IResumable* aOnResume) override;

image/moz.build

@@ -47,6 +47,7 @@ EXPORTS += [
 ]
 
 UNIFIED_SOURCES += [
+    'AnimationFrameBuffer.cpp',
     'AnimationSurfaceProvider.cpp',
     'ClippedImage.cpp',
     'DecodedSurfaceProvider.cpp',

modules/libpref/init/all.js

@@ -4187,6 +4187,15 @@ pref("toolkit.zoomManager.zoomValues", ".3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2
 // Image-related prefs
 //
 
+// The maximum size (in kB) that the aggregate frames of an animation can use
+// before it starts to discard already displayed frames and redecode them as
+// necessary.
+pref("image.animated.decode-on-demand.threshold-kb", 262144);
+
+// The minimum number of frames we want to have buffered ahead of an
+// animation's currently displayed frame.
+pref("image.animated.decode-on-demand.batch-size", 6);
+
 // The maximum size, in bytes, of the decoded images we cache
 pref("image.cache.size", 5242880);