cc: Add image decode control in the compositor.

cc/tiles/image_decode_controller.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/tiles/image_decode_controller.h"
 
+#include "base/memory/discardable_memory.h"
 #include "cc/debug/devtools_instrumentation.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkImage.h"
 
 namespace cc {
 namespace {
 
+// The amount of memory we can lock ahead of time (128MB). This limit is only
+// used to inform the caller of the amount of space available in the cache. The
+// caller can still request tasks which can cause this limit to be breached.
+const size_t kLockedMemoryLimitBytes = 128 * 1024 * 1024;
+
+// The largest single high quality image to try and process. Images above this
+// size will drop down to medium quality.
+const size_t kMaxHighQualityImageSizeBytes = 64 * 1024 * 1024;
+
+// The number of entries to keep around in the cache. This limit can be breached
+// if more items are locked. That is, locked items ignore this limit.
+const size_t kMaxItemsInCache = 100;
+
 class ImageDecodeTaskImpl : public ImageDecodeTask {
  public:
   ImageDecodeTaskImpl(ImageDecodeController* controller,
-                      const SkImage* image,
-                      int layer_id,
+                      const ImageDecodeController::ImageKey& image_key,
+                      const DrawImage& image,
                       uint64_t source_prepare_tiles_id)
       : controller_(controller),
-        image_(skia::SharePtr(image)),
-        layer_id_(layer_id),
+        image_key_(image_key),
+        image_(image),
+        image_ref_(skia::SharePtr(image.image())),
         source_prepare_tiles_id_(source_prepare_tiles_id) {}
 
   // Overridden from Task:
   void RunOnWorkerThread() override {
     TRACE_EVENT1("cc", "ImageDecodeTaskImpl::RunOnWorkerThread",
                  "source_prepare_tiles_id", source_prepare_tiles_id_);
     devtools_instrumentation::ScopedImageDecodeTask image_decode_task(
-        image_.get());
-    controller_->DecodeImage(image_.get());
-
-    // Release the reference after decoding image to ensure that it is not kept
-    // alive unless needed.
-    image_.clear();
+        image_ref_.get());
+    controller_->DecodeImage(image_key_, image_);
   }
 
   // Overridden from TileTask:
   void ScheduleOnOriginThread(TileTaskClient* client) override {}
   void CompleteOnOriginThread(TileTaskClient* client) override {
-    controller_->OnImageDecodeTaskCompleted(layer_id_, image_.get(),
-                                            !HasFinishedRunning());
+    controller_->RemovePendingTask(image_key_);
   }
 
  protected:
   ~ImageDecodeTaskImpl() override {}
 
  private:
   ImageDecodeController* controller_;
-  skia::RefPtr<const SkImage> image_;
-  int layer_id_;
+  ImageDecodeController::ImageKey image_key_;
+  DrawImage image_;
+  skia::RefPtr<const SkImage> image_ref_;
   uint64_t source_prepare_tiles_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecodeTaskImpl);
 };
 
+template <typename Type>
+typename std::deque<Type>::iterator FindImage(
+    std::deque<Type>* collection,
+    const ImageDecodeControllerKey& key) {
+  return std::find_if(collection->begin(), collection->end(),
+                      [key](const Type& image) { return image.first == key; });
+}
+
+SkSize GetScaleAdjustment(const ImageDecodeControllerKey& key,
+                          const SkImage* original_image) {
+  float x_scale =
+      key.target_size().width() / static_cast<float>(original_image->width());
+  float y_scale =
+      key.target_size().height() / static_cast<float>(original_image->height());
+  return SkSize::Make(x_scale, y_scale);
+}
+
 }  // namespace
 
-ImageDecodeController::ImageDecodeController() {}
-
-ImageDecodeController::~ImageDecodeController() {}
-
-scoped_refptr<ImageDecodeTask> ImageDecodeController::GetTaskForImage(
+ImageDecodeController::ImageDecodeController()
+    : is_using_gpu_rasterization_(false),
+      locked_images_budget_(kLockedMemoryLimitBytes) {}
+
+ImageDecodeController::~ImageDecodeController() {
+  DCHECK_EQ(0u, decoded_images_ref_counts_.size());
+  DCHECK_EQ(0u, at_raster_decoded_images_ref_counts_.size());
+}
+
+bool ImageDecodeController::GetTaskForImageAndRef(
     const DrawImage& image,
-    int layer_id,
-    uint64_t prepare_tiles_id) {
-  uint32_t generation_id = image.image()->uniqueID();
-  scoped_refptr<ImageDecodeTask>& decode_task =
-      image_decode_tasks_[layer_id][generation_id];
-  if (!decode_task)
-    decode_task = CreateTaskForImage(image.image(), layer_id, prepare_tiles_id);
-  return decode_task;
-}
-
-scoped_refptr<ImageDecodeTask> ImageDecodeController::CreateTaskForImage(
-    const SkImage* image,
-    int layer_id,
-    uint64_t prepare_tiles_id) {
+    uint64_t prepare_tiles_id,
+    scoped_refptr<ImageDecodeTask>* task) {
+  // If the image already exists or if we're going to create a task for it, then

[ericrk, 2015/12/04 00:50:46]

this line is a bit unclear - you say "if we're going to create a task for it,
then we need to ref...", but just below we create a ImageDecodeTaskImpl to
preroll, but don't ref... I get the preroll part, but maybe this comment needs a
few more details?

+  // we need to ref this image. That means the image is or will be in the cache.
+  // When the ref goes to 0, it will be unpinned but will remain in the cache.
+  // If the image does not fit into the budget, then we don't ref this image,
+  // since it will be decoded at raster time which is when it will be
+  // temporarily put in the cache.
+  ImageKey key = ImageKey::FromDrawImage(image);
+  TRACE_EVENT1("cc", "ImageDecodeController::GetTaskForImageAndRef", "key",
+               key.ToString());
+  // If we're not going to do a scale, we will just create a task to preroll the
+  // image the first time we see it. This doesn't need to account for memory.
+  // TODO(vmpstr): We can also lock the original sized image, in which case it
+  // does require memory bookkeeping.
+  if (!ShouldDecodeAndScaleImage(key, image)) {
+    base::AutoLock lock(lock_);
+    if (prerolled_images_.count(key.image_id()) == 0) {
+      scoped_refptr<ImageDecodeTask>& existing_task = pending_image_tasks_[key];
+      if (!existing_task) {
+        existing_task = make_scoped_refptr(
+            new ImageDecodeTaskImpl(this, key, image, prepare_tiles_id));
+      }
+      *task = existing_task;
+    } else {
+      *task = nullptr;
+    }
+    return false;
+  }
+
+  base::AutoLock lock(lock_);
+
+  // If we already have the image in cache, then we can return it.
+  auto decoded_it = FindImage(&decoded_images_, key);
+  bool new_image_fits_in_memory =
+      locked_images_budget_.AvailableMemoryBytes() >= key.target_bytes();
+  if (decoded_it != decoded_images_.end()) {
+    if (decoded_it->second->is_locked() ||
+        (new_image_fits_in_memory && decoded_it->second->Lock())) {
+      RefImage(key);
+      *task = nullptr;
+      SanityCheckState(__LINE__, true);
+      return true;
+    }
+    // If the image fits in memory, then we at least tried to lock it and
+    // failed. This means that it's not valid anymore.
+    if (new_image_fits_in_memory)
+      decoded_images_.erase(decoded_it);
+  }
+
+  // If the task exists, return it.
+  scoped_refptr<ImageDecodeTask>& existing_task = pending_image_tasks_[key];
+  if (existing_task) {
+    RefImage(key);
+    *task = existing_task;
+    SanityCheckState(__LINE__, true);
+    return true;
+  }
+
+  // At this point, we have to create a new image/task, so we need to abort if
+  // it doesn't fit into memory and there are currently no raster tasks that
+  // would have already accounted for memory. The latter part is possible if
+  // there's a running raster task that could not be canceled, and still has a
+  // ref to the image that is now being reffed for the new schedule.
+  if (!new_image_fits_in_memory && (decoded_images_ref_counts_.find(key) ==
+                                    decoded_images_ref_counts_.end())) {
+    *task = nullptr;
+    SanityCheckState(__LINE__, true);
+    return false;
+  }
+
+  // Actually create the task. RefImage will account for memory on the first
+  // ref.
+  RefImage(key);
+  existing_task = make_scoped_refptr(
+      new ImageDecodeTaskImpl(this, key, image, prepare_tiles_id));
+  *task = existing_task;
+  SanityCheckState(__LINE__, true);
+  return true;
+}
+
+void ImageDecodeController::RefImage(const ImageKey& key) {
+  TRACE_EVENT1("cc", "ImageDecodeController::RefImage", "key", key.ToString());
+  lock_.AssertAcquired();
+  int ref = ++decoded_images_ref_counts_[key];
+  if (ref == 1) {
+    DCHECK_GE(locked_images_budget_.AvailableMemoryBytes(), key.target_bytes());
+    locked_images_budget_.AddUsage(key.target_bytes());
+  }
+}
+
+void ImageDecodeController::UnrefImage(const DrawImage& image) {
+  // When we unref the image, there are several situations we need to consider:
+  // 1. The ref did not reach 0, which means we have to keep the image locked.
+  // 2. The ref reached 0, we should unlock it.
+  //   2a. The image isn't in the locked cache because we didn't get to decode
+  //       it yet.
+  //   2b. Unlock the image but keep it in list.
+  const ImageKey& key = ImageKey::FromDrawImage(image);
+  DCHECK(ShouldDecodeAndScaleImage(key, image));
+  TRACE_EVENT1("cc", "ImageDecodeController::UnrefImage", "key",
+               key.ToString());
+
+  base::AutoLock lock(lock_);
+  auto ref_count_it = decoded_images_ref_counts_.find(key);
+  DCHECK(ref_count_it != decoded_images_ref_counts_.end());
+
+  --ref_count_it->second;
+  if (ref_count_it->second == 0) {
+    decoded_images_ref_counts_.erase(ref_count_it);
+    locked_images_budget_.SubtractUsage(key.target_bytes());
+
+    auto decoded_image_it = FindImage(&decoded_images_, key);
+    // If we've never decoded the image before ref reached 0, then we wouldn't
+    // have it in our cache. This would happen if we canceled tasks.
+    if (decoded_image_it == decoded_images_.end()) {
+      SanityCheckState(__LINE__, true);
+      return;
+    }
+    DCHECK(decoded_image_it->second->is_locked());
+    decoded_image_it->second->Unlock();
+  }
+  SanityCheckState(__LINE__, true);
+}
+
+void ImageDecodeController::DecodeImage(const ImageKey& key,
+                                        const DrawImage& image) {
+  TRACE_EVENT1("cc", "ImageDecodeController::DecodeImage", "key",
+               key.ToString());
+  if (!ShouldDecodeAndScaleImage(key, image)) {
+    image.image()->preroll();
+
+    base::AutoLock lock(lock_);
+    prerolled_images_.insert(key.image_id());
+    // Erase the pending task from the queue, since the task won't be doing
+    // anything useful after this function terminates. Since we don't preroll
+    // images twice, this is actually not necessary but it behaves similar to
+    // the other code path: when this function finishes, the task isn't in the
+    // pending_image_tasks_ list.
+    pending_image_tasks_.erase(key);
+    return;
+  }
+
+  base::AutoLock lock(lock_);
+
+  auto image_it = FindImage(&decoded_images_, key);
+  if (image_it != decoded_images_.end()) {
+    if (image_it->second->is_locked() || image_it->second->Lock()) {
+      pending_image_tasks_.erase(key);
+      return;
+    }
+    decoded_images_.erase(image_it);
+  }
+
+  scoped_refptr<DecodedImage> decoded_image;
+  {
+    base::AutoUnlock unlock(lock_);
+    decoded_image = DecodeImageInternal(key, image.image());
+  }
+
+  // Erase the pending task from the queue, since the task won't be doing
+  // anything useful after this function terminates. That is, if this image
+  // needs to be decoded again, we have to create a new task.
+  pending_image_tasks_.erase(key);
+
+  // We could have finished all of the raster tasks (cancelled) while this image
+  // decode task was running, which means that we now have a locked image but no
+  // ref counts. Unlock it immediately in this case.
+  if (decoded_images_ref_counts_.find(key) ==
+      decoded_images_ref_counts_.end()) {
+    decoded_image->Unlock();
+  }
+
+  // At this point, it could have been the case that this image was decoded in
+  // place by an already running raster task from a previous schedule. If that's
+  // the case, then it would have already been placed into the cache (possibly
+  // locked). Remove it if that was the case.
+  image_it = FindImage(&decoded_images_, key);
+  if (image_it != decoded_images_.end()) {
+    if (image_it->second->is_locked() || image_it->second->Lock()) {
+      pending_image_tasks_.erase(key);
+      return;
+    }
+    decoded_images_.erase(image_it);
+  }
+  decoded_images_.push_back(AnnotatedDecodedImage(key, decoded_image));
+  SanityCheckState(__LINE__, true);
+}
+
+scoped_refptr<ImageDecodeController::DecodedImage>
+ImageDecodeController::DecodeImageInternal(const ImageKey& key,
+                                           const SkImage* image) {
+  TRACE_EVENT1("cc", "ImageDecodeController::DecodeImageInternal", "key",
+               key.ToString());
+
+  // Get the decoded image first (at the original scale).
+  SkImageInfo decoded_info =
+      SkImageInfo::MakeN32Premul(image->width(), image->height());
+  scoped_ptr<uint8_t[]> decoded_pixels(
+      new uint8_t[decoded_info.minRowBytes() * decoded_info.height()]);
+  bool result = image->readPixels(decoded_info, decoded_pixels.get(),
+                                  decoded_info.minRowBytes(), 0, 0,
+                                  SkImage::kAllow_CachingHint);
+  DCHECK(result);
+
+  skia::RefPtr<SkImage> decoded_image = skia::AdoptRef(SkImage::NewFromRaster(
+      decoded_info, decoded_pixels.get(), decoded_info.minRowBytes(),
+      [](const void* pixels, void* context) {}, nullptr));
+
+  // Now scale the pixels into the destination size.
+  SkImageInfo scaled_info = SkImageInfo::MakeN32Premul(
+      key.target_size().width(), key.target_size().height());
+  scoped_ptr<base::DiscardableMemory> scaled_pixels =
+      base::DiscardableMemoryAllocator::GetInstance()
+          ->AllocateLockedDiscardableMemory(scaled_info.minRowBytes() *
+                                            scaled_info.height());
+  SkPixmap scaled_pixmap(scaled_info, scaled_pixels->data(),
+                         scaled_info.minRowBytes());
+  // TODO(vmpstr): Start handling more than just high filter quality.
+  DCHECK_EQ(kHigh_SkFilterQuality, key.filter_quality());
+  result = decoded_image->scalePixels(scaled_pixmap, kHigh_SkFilterQuality,
+                                      SkImage::kDisallow_CachingHint);
+  DCHECK(result);
   return make_scoped_refptr(
-      new ImageDecodeTaskImpl(this, image, layer_id, prepare_tiles_id));
-}
-
-void ImageDecodeController::DecodeImage(const SkImage* image) {
-  image->preroll();
-}
-
-void ImageDecodeController::AddLayerUsedCount(int layer_id) {
-  ++used_layer_counts_[layer_id];
-}
-
-void ImageDecodeController::SubtractLayerUsedCount(int layer_id) {
-  if (--used_layer_counts_[layer_id])
+      new DecodedImage(scaled_info, std::move(scaled_pixels)));
+}
+
+DecodedDrawImage ImageDecodeController::GetDecodedImageForDraw(
+    const DrawImage& draw_image) {
+  ImageKey key = ImageKey::FromDrawImage(draw_image);
+  TRACE_EVENT1("cc", "ImageDecodeController::GetDecodedImageAndRef", "key",
+               key.ToString());
+  if (!ShouldDecodeAndScaleImage(key, draw_image)) {
+    return DecodedDrawImage(draw_image.image(), SkSize::Make(1.f, 1.f),
+                            draw_image.filter_quality());
+  }
+
+  base::AutoLock lock(lock_);
+  auto decoded_images_it = FindImage(&decoded_images_, key);
+  // If we found the image and it's locked, then return it. If it's not locked,
+  // erase it from the cache since it might be put into the at-raster cache.
+  scoped_refptr<DecodedImage> decoded_image;
+  if (decoded_images_it != decoded_images_.end()) {
+    decoded_image = decoded_images_it->second;
+    if (decoded_image->is_locked()) {
+      RefImage(key);
+      SanityCheckState(__LINE__, true);
+      return DecodedDrawImage(decoded_image->image(),
+                              GetScaleAdjustment(key, draw_image.image()),
+                              kLow_SkFilterQuality);
+    } else {
+      decoded_images_.erase(decoded_images_it);
+    }
+  }
+
+  // See if another thread already decoded this image at raster time. If so, we
+  // can just use that result directly.
+  auto at_raster_images_it = FindImage(&at_raster_decoded_images_, key);
+  if (at_raster_images_it != at_raster_decoded_images_.end()) {
+    DCHECK(at_raster_images_it->second->is_locked());
+    RefAtRasterImage(key);
+    SanityCheckState(__LINE__, true);
+    auto decoded_draw_image = DecodedDrawImage(
+        at_raster_images_it->second->image(),
+        GetScaleAdjustment(key, draw_image.image()), kLow_SkFilterQuality);
+    decoded_draw_image.set_at_raster_decode(true);
+    return decoded_draw_image;
+  }
+
+  // Now we know that we don't have a locked image, and we seem to be the first
+  // thread encountering this image (that might not be true, since other threads
+  // might be decoding it already). This means that we need to decode the image
+  // assuming we can't lock the one we found in the cache.
+  bool check_at_raster_cache = false;
+  if (!decoded_image || !decoded_image->Lock()) {
+    // Note that we have to release the lock, since this lock is also accessed
+    // on the compositor thread. This means holding on to the lock might stall
+    // the compositor thread for the duration of the decode!
+    base::AutoUnlock unlock(lock_);
+    decoded_image = DecodeImageInternal(key, draw_image.image());
+    check_at_raster_cache = true;
+  }
+
+  // While we unlocked the lock, it could be the case that another thread
+  // already decoded this already and put it in the at-raster cache. Look it up
+  // first.
+  bool need_to_add_image_to_cache = true;
+  if (check_at_raster_cache) {
+    at_raster_images_it = FindImage(&at_raster_decoded_images_, key);
+    if (at_raster_images_it != at_raster_decoded_images_.end()) {
+      // We have to drop our decode, since the one in the cache is being used by
+      // another thread.
+      decoded_image->Unlock();
+      decoded_image = at_raster_images_it->second;
+      need_to_add_image_to_cache = false;
+    }
+  }
+
+  // If we really are the first ones, or if the other thread already unlocked
+  // the image, then put our work into at-raster time cache.
+  if (need_to_add_image_to_cache) {
+    at_raster_decoded_images_.push_back(
+        AnnotatedDecodedImage(key, decoded_image));
+  }
+
+  DCHECK(decoded_image);
+  DCHECK(decoded_image->is_locked());
+  RefAtRasterImage(key);
+  SanityCheckState(__LINE__, true);
+  auto decoded_draw_image = DecodedDrawImage(
+      decoded_image->image(), GetScaleAdjustment(key, draw_image.image()),
+      kLow_SkFilterQuality);
+  decoded_draw_image.set_at_raster_decode(true);
+  return decoded_draw_image;
+}
+
+void ImageDecodeController::DrawWithImageFinished(
+    const DrawImage& image,
+    const DecodedDrawImage& decoded_image) {
+  TRACE_EVENT1("cc", "ImageDecodeController::DrawWithImageFinished", "key",
+               ImageKey::FromDrawImage(image).ToString());
+  ImageKey key = ImageKey::FromDrawImage(image);
+  if (!ShouldDecodeAndScaleImage(key, image))
     return;
 
-  // Clean up decode tasks once a layer is no longer used.
-  used_layer_counts_.erase(layer_id);
-  image_decode_tasks_.erase(layer_id);
-}
-
-void ImageDecodeController::OnImageDecodeTaskCompleted(int layer_id,
-                                                       const SkImage* image,
-                                                       bool was_canceled) {
-  // If the task has successfully finished, then keep the task until the layer
-  // is no longer in use. This ensures that we only decode a image once.
-  // TODO(vmpstr): Remove this when decode lifetime is controlled by cc.
-  if (!was_canceled)
+  if (decoded_image.is_at_raster_decode())
+    UnrefAtRasterImage(key);
+  else
+    UnrefImage(image);
+  SanityCheckState(__LINE__, false);
+}
+
+void ImageDecodeController::RefAtRasterImage(const ImageKey& key) {
+  TRACE_EVENT1("cc", "ImageDecodeController::RefAtRasterImage", "key",
+               key.ToString());
+  DCHECK(FindImage(&at_raster_decoded_images_, key) !=
+         at_raster_decoded_images_.end());
+  ++at_raster_decoded_images_ref_counts_[key];
+}
+
+void ImageDecodeController::UnrefAtRasterImage(const ImageKey& key) {
+  TRACE_EVENT1("cc", "ImageDecodeController::UnrefAtRasterImage", "key",
+               key.ToString());
+  base::AutoLock lock(lock_);
+
+  auto ref_it = at_raster_decoded_images_ref_counts_.find(key);
+  DCHECK(ref_it != at_raster_decoded_images_ref_counts_.end());
+  --ref_it->second;
+  if (ref_it->second == 0) {
+    at_raster_decoded_images_ref_counts_.erase(ref_it);
+    auto at_raster_image_it = FindImage(&at_raster_decoded_images_, key);
+    DCHECK(at_raster_image_it != at_raster_decoded_images_.end());
+
+    // The ref for our image reached 0 and it's still locked. We need to figure
+    // out what the best thing to do with the image. There are several
+    // situations:
+    // 1. The image is not in the main cache and...
+    //    1a. ... its ref count is 0: unlock our image and put it in the main
+    //    cache.
+    //    1b. ... ref count is not 0: keep the image locked and put it in the
+    //    main cache.
+    // 2. The image is in the main cache...
+    //    2a. ... and is locked: unlock our image and discard it
+    //    2b. ... and is unlocked and...
+    //       2b1. ... its ref count is 0: unlock our image and replace the
+    //       existing one with ours.
+    //       2b2. ... its ref count is not 0: this shouldn't be possible.
+    auto image_it = FindImage(&decoded_images_, key);
+    if (image_it == decoded_images_.end()) {
+      if (decoded_images_ref_counts_.find(key) ==
+          decoded_images_ref_counts_.end()) {
+        at_raster_image_it->second->Unlock();
+      }
+      decoded_images_.push_back(*at_raster_image_it);
+    } else if (image_it->second->is_locked()) {
+      at_raster_image_it->second->Unlock();
+    } else {
+      DCHECK(decoded_images_ref_counts_.find(key) ==
+             decoded_images_ref_counts_.end());
+      at_raster_image_it->second->Unlock();
+      decoded_images_.erase(image_it);
+      decoded_images_.push_back(*at_raster_image_it);
+    }
+    at_raster_decoded_images_.erase(at_raster_image_it);
+  }
+}
+
+bool ImageDecodeController::ShouldDecodeAndScaleImage(const ImageKey& key,
+                                                      const DrawImage& image) {
+  // TODO(vmpstr): Handle GPU rasterization.
+  if (is_using_gpu_rasterization_)
+    return false;
+  if (!CanHandleFilterQuality(key.filter_quality()))
+    return false;
+  return true;
+}
+
+bool ImageDecodeController::CanHandleFilterQuality(
+    SkFilterQuality filter_quality) {
+  // We don't need to handle low quality filters.
+  if (filter_quality == kLow_SkFilterQuality ||
+      filter_quality == kNone_SkFilterQuality) {
+    return false;
+  }
+
+  // TODO(vmpstr): We need to start caching mipmaps for medium quality and
+  // caching the interpolated values from those. For now, we don't have this.
+  if (filter_quality == kMedium_SkFilterQuality)
+    return false;
+  DCHECK(filter_quality == kHigh_SkFilterQuality);
+  return true;
+}
+
+void ImageDecodeController::ReduceCacheUsage() {
+  TRACE_EVENT0("cc", "ImageDecodeController::ReduceCacheUsage");
+  base::AutoLock lock(lock_);
+  size_t num_to_remove = (decoded_images_.size() > kMaxItemsInCache)
+                             ? (decoded_images_.size() - kMaxItemsInCache)
+                             : 0;
+  for (auto it = decoded_images_.begin();
+       num_to_remove != 0 && it != decoded_images_.end();) {
+    if (it->second->is_locked()) {
+      ++it;
+      continue;
+    }
+
+    it = decoded_images_.erase(it);
+    --num_to_remove;
+  }
+}
+
+void ImageDecodeController::RemovePendingTask(const ImageKey& key) {
+  base::AutoLock lock(lock_);
+  pending_image_tasks_.erase(key);
+}
+
+void ImageDecodeController::SetIsUsingGpuRasterization(
+    bool is_using_gpu_rasterization) {
+  if (is_using_gpu_rasterization_ == is_using_gpu_rasterization)
     return;
-
-  // Otherwise, we have to clean up the task so that a new one can be created if
-  // we need to decode the image again.
-  LayerImageTaskMap::iterator layer_it = image_decode_tasks_.find(layer_id);
-  if (layer_it == image_decode_tasks_.end())
-    return;
-
-  ImageTaskMap& image_tasks = layer_it->second;
-  ImageTaskMap::iterator task_it = image_tasks.find(image->uniqueID());
-  if (task_it == image_tasks.end())
-    return;
-  image_tasks.erase(task_it);
+  is_using_gpu_rasterization_ = is_using_gpu_rasterization;
+
+  base::AutoLock lock(lock_);
+
+  DCHECK_EQ(0u, decoded_images_ref_counts_.size());
+  DCHECK_EQ(0u, at_raster_decoded_images_ref_counts_.size());
+  DCHECK(std::find_if(decoded_images_.begin(), decoded_images_.end(),
+                      [](const AnnotatedDecodedImage& image) {
+                        return image.second->is_locked();
+                      }) == decoded_images_.end());
+  DCHECK(std::find_if(at_raster_decoded_images_.begin(),
+                      at_raster_decoded_images_.end(),
+                      [](const AnnotatedDecodedImage& image) {
+                        return image.second->is_locked();
+                      }) == at_raster_decoded_images_.end());
+  decoded_images_.clear();
+  at_raster_decoded_images_.clear();
+}
+
+size_t ImageDecodeController::SanityCheckState(int line, bool lock_acquired) {
+#if DCHECK_IS_ON()
+  if (!lock_acquired) {
+    base::AutoLock lock(lock_);
+    return SanityCheckState(line, true);
+  }
+
+  MemoryBudget budget(kLockedMemoryLimitBytes);
+  for (const auto& annotated_image : decoded_images_) {
+    auto ref_it = decoded_images_ref_counts_.find(annotated_image.first);
+    if (annotated_image.second->is_locked()) {
+      budget.AddUsage(annotated_image.first.target_bytes());
+      DCHECK(ref_it != decoded_images_ref_counts_.end()) << line;
+    } else {
+      DCHECK(ref_it == decoded_images_ref_counts_.end() ||
+             pending_image_tasks_.find(annotated_image.first) !=
+                 pending_image_tasks_.end())
+          << line;
+    }
+  }
+  DCHECK_GE(budget.AvailableMemoryBytes(),
+            locked_images_budget_.AvailableMemoryBytes())
+      << line;
+  return budget.AvailableMemoryBytes();
+#else
+  return 0u;
+#endif  // DCHECK_IS_ON()
+}
+
+// ImageDecodeControllerKey
+ImageDecodeControllerKey ImageDecodeControllerKey::FromDrawImage(
+    const DrawImage& image) {
+  const SkSize& scale = image.scale();
+  gfx::Size target_size(
+      std::abs(SkScalarRoundToInt(image.image()->width() * scale.width())),

[ericrk, 2015/12/04 00:50:46]

maybe this is fine, but SkScalarRoundToInt is defined as:

#define SkScalarRoundToInt(x)       (int)floor((x) + 0.5)

this means that an image with width 1.0f and scale 0.5f will end up with a size
of 1.0f, while a scale of -0.5f would result in a size of 0.0f.

Would be consistent if you took the abs of the multiplication, before rounding.
- not sure what behavior is desired.

+      std::abs(SkScalarRoundToInt(image.image()->height() * scale.height())));
+
+  // Start with the quality that was requested, but drop down immediately to low
+  // if we're not actually going to do any scale.
+  SkFilterQuality quality = image.filter_quality();
+  if (target_size.width() == image.image()->width() &&
+      target_size.height() == image.image()->height()) {
+    quality = std::min(quality, kLow_SkFilterQuality);
+  }
+
+  // Drop from high to medium if the image has perspective applied, the matrix
+  // we applied wasn't decomposable, or if the scaled image will be too large.
+  if (quality == kHigh_SkFilterQuality) {
+    if (image.matrix_has_perspective() || !image.matrix_is_decomposable()) {
+      quality = kMedium_SkFilterQuality;
+    } else {
+      base::CheckedNumeric<size_t> size = 4u;
+      size *= target_size.width();
+      size *= target_size.height();
+      if (size.ValueOrDefault(std::numeric_limits<size_t>::max()) >
+          kMaxHighQualityImageSizeBytes) {
+        quality = kMedium_SkFilterQuality;
+      }
+    }
+  }
+
+  // Drop from medium to low if the matrix we applied wasn't decomposable or if
+  // we're enlarging the image in both dimensions.
+  if (quality == kMedium_SkFilterQuality) {
+    if (!image.matrix_is_decomposable() ||
+        (scale.width() >= 1.f && scale.height() >= 1.f)) {
+      quality = kLow_SkFilterQuality;
+    }
+  }
+
+  return ImageDecodeControllerKey(image.image()->uniqueID(), target_size,
+                                  quality);
+}
+
+ImageDecodeControllerKey::ImageDecodeControllerKey(
+    uint32_t image_id,
+    const gfx::Size& size,
+    SkFilterQuality filter_quality)
+    : image_id_(image_id), size_(size), filter_quality_(filter_quality) {}
+
+std::string ImageDecodeControllerKey::ToString() const {
+  std::ostringstream str;
+  str << "id[" << image_id_ << "] size[" << size_.width() << "x"
+      << size_.height() << "] filter_quality[" << filter_quality_ << "]";
+  return str.str();
+}
+
+// DecodedImage
+ImageDecodeController::DecodedImage::DecodedImage(
+    const SkImageInfo& info,
+    scoped_ptr<base::DiscardableMemory> memory)
+    : locked_(true), image_info_(info), memory_(memory.Pass()) {
+  image_ = skia::AdoptRef(SkImage::NewFromRaster(
+      image_info_, memory_->data(), image_info_.minRowBytes(),
+      [](const void* pixels, void* context) {}, nullptr));
+}
+
+ImageDecodeController::DecodedImage::~DecodedImage() {}
+
+bool ImageDecodeController::DecodedImage::Lock() {
+  DCHECK(!locked_);
+  bool success = memory_->Lock();
+  if (!success)
+    return false;
+  locked_ = true;
+  return true;
+}
+
+void ImageDecodeController::DecodedImage::Unlock() {
+  DCHECK(locked_);
+  memory_->Unlock();
+  locked_ = false;
+}
+
+// MemoryBudget
+ImageDecodeController::MemoryBudget::MemoryBudget(size_t limit_bytes)
+    : limit_bytes_(limit_bytes), current_usage_bytes_(0u) {}
+
+size_t ImageDecodeController::MemoryBudget::AvailableMemoryBytes() const {
+  size_t usage = GetCurrentUsageSafe();
+  return usage >= limit_bytes_ ? 0u : (limit_bytes_ - usage);
+}
+
+void ImageDecodeController::MemoryBudget::AddUsage(size_t usage) {
+  current_usage_bytes_ += usage;
+}
+
+void ImageDecodeController::MemoryBudget::SubtractUsage(size_t usage) {
+  DCHECK_GE(current_usage_bytes_.ValueOrDefault(0u), usage);
+  current_usage_bytes_ -= usage;
+}
+
+void ImageDecodeController::MemoryBudget::ResetUsage() {
+  current_usage_bytes_ = 0;
+}
+
+size_t ImageDecodeController::MemoryBudget::GetCurrentUsageSafe() const {
+  return current_usage_bytes_.ValueOrDie();
 }
 
 }  // namespace cc