Gpu Image Decode Controller

cc/tiles/gpu_image_decode_controller.cc

Index: cc/tiles/gpu_image_decode_controller.cc
diff --git a/cc/tiles/gpu_image_decode_controller.cc b/cc/tiles/gpu_image_decode_controller.cc
index da9bd207010071c937c8c6490c1d6511db1b7ab8..c2684c9bf40fd2e6bc6c7241b13004692656859b 100644
--- a/cc/tiles/gpu_image_decode_controller.cc
+++ b/cc/tiles/gpu_image_decode_controller.cc
@@ -4,35 +4,81 @@
 
 #include "cc/tiles/gpu_image_decode_controller.h"
 
+#include "base/memory/discardable_memory_allocator.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/strings/stringprintf.h"
+#include "base/thread_task_runner_handle.h"
 #include "cc/debug/devtools_instrumentation.h"
+#include "cc/output/context_provider.h"
 #include "cc/raster/tile_task_runner.h"
+#include "gpu/command_buffer/client/context_support.h"
+#include "gpu/command_buffer/client/gles2_interface.h"
+#include "gpu_image_decode_controller.h"
 #include "skia/ext/refptr.h"
+#include "skia/ext/texture_handle.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkSurface.h"
+#include "third_party/skia/include/gpu/GrContext.h"
+#include "third_party/skia/include/gpu/GrTexture.h"
+#include "ui/gfx/skia_util.h"
+#include "ui/gl/trace_util.h"
 
 namespace cc {
+namespace {
 
+static const int kMaxGpuImageBytes = 1024 * 1024 * 96;
+static const int kMaxDiscardableItems = 1000;
+
+// Returns true if an image would not be drawn and should therefore be
+// skipped rather than decoded.
+bool SkipImage(const DrawImage& draw_image) {
+  if (!SkIRect::Intersects(draw_image.src_rect(), draw_image.image()->bounds()))
+    return true;
+  if (draw_image.matrix_is_decomposable() &&

[vmpstr, 2016/03/28 23:55:52]

If matrix is not decomposable, then the scale is set to (1.f, 1.f) so I don't
think you need this particular term. 

[ericrk, 2016/03/29 23:11:29]

ah, good point.

+      (std::abs(draw_image.scale().width()) <
+           std::numeric_limits<float>::epsilon() ||
+       std::abs(draw_image.scale().height()) <
+           std::numeric_limits<float>::epsilon()))

[vmpstr, 2016/03/28 23:55:53]

Can you add braces for this if-statement please?

[ericrk, 2016/03/29 23:11:30]

Done.

+    return true;
+  return false;
+}
+
+SkImage::DeferredTextureImageUsageParams ParamsFromDrawImage(
+    const DrawImage& draw_image) {
+  SkImage::DeferredTextureImageUsageParams params;
+  params.fMatrix = draw_image.matrix();
+  params.fQuality = draw_image.filter_quality();
+
+  return params;
+}
+
+}  // namespace
+
+// Task which decodes an image and stores the result in discardable memory.
+// This task does not use GPU resources and can be run on any thread.
 class ImageDecodeTaskImpl : public ImageDecodeTask {
  public:
   ImageDecodeTaskImpl(GpuImageDecodeController* controller,
-                      const DrawImage& image,
+                      const DrawImage& draw_image,
                       uint64_t source_prepare_tiles_id)
       : controller_(controller),
-        image_(image),
-        image_ref_(skia::SharePtr(image.image())),
-        source_prepare_tiles_id_(source_prepare_tiles_id) {}
+        image_(draw_image),
+        image_ref_(skia::SharePtr(draw_image.image())),
+        source_prepare_tiles_id_(source_prepare_tiles_id) {
+    DCHECK(!SkipImage(draw_image));
+  }
 
   // Overridden from Task:
   void RunOnWorkerThread() override {
     TRACE_EVENT2("cc", "ImageDecodeTaskImpl::RunOnWorkerThread", "mode", "gpu",
                  "source_prepare_tiles_id", source_prepare_tiles_id_);
-    devtools_instrumentation::ScopedImageDecodeTask image_decode_task(
-        image_ref_.get());
     controller_->DecodeImage(image_);
   }
 
   // Overridden from TileTask:
   void ScheduleOnOriginThread(TileTaskClient* client) override {}
   void CompleteOnOriginThread(TileTaskClient* client) override {
-    controller_->RemovePendingTaskForImage(image_);
+    controller_->DecodeTaskCompleted(image_);
   }
 
  protected:
@@ -42,61 +88,590 @@ class ImageDecodeTaskImpl : public ImageDecodeTask {
   GpuImageDecodeController* controller_;
   DrawImage image_;
   skia::RefPtr<const SkImage> image_ref_;
-  uint64_t source_prepare_tiles_id_;
+  const uint64_t source_prepare_tiles_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecodeTaskImpl);
 };
 
-GpuImageDecodeController::GpuImageDecodeController() {}
+// Task which creates an image from decoded data. Typically this involves
+// uploading data to the GPU, which requires this task be run on the non-
+// concurrent thread.
+class ImageUploadTaskImpl : public ImageDecodeTask {
+ public:
+  ImageUploadTaskImpl(GpuImageDecodeController* controller,
+                      const DrawImage& draw_image,
+                      scoped_refptr<ImageDecodeTask> decode_dependency,
+                      uint64_t source_prepare_tiles_id)
+      : ImageDecodeTask(std::move(decode_dependency)),
+        controller_(controller),
+        image_(draw_image),
+        image_ref_(skia::SharePtr(draw_image.image())),
+        source_prepare_tiles_id_(source_prepare_tiles_id) {
+    DCHECK(!SkipImage(draw_image));
+  }
+
+  // Override from Task:
+  void RunOnWorkerThread() override {
+    TRACE_EVENT2("cc", "ImageUploadTaskImpl::RunOnWorkerThread", "mode", "gpu",
+                 "source_prepare_tiles_id", source_prepare_tiles_id_);
+    controller_->UploadImage(image_);
+  }
+
+  void ScheduleOnOriginThread(TileTaskClient* client) override {}
+  void CompleteOnOriginThread(TileTaskClient* client) override {
+    controller_->UploadTaskCompleted(image_);
+  }
+
+  // Override from ImageDecodeTask:
+  bool SupportsConcurrentExecution() const override { return false; }
+
+ protected:
+  ~ImageUploadTaskImpl() override {}
+
+ private:
+  GpuImageDecodeController* controller_;
+  DrawImage image_;
+  skia::RefPtr<const SkImage> image_ref_;
+  uint64_t source_prepare_tiles_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(ImageUploadTaskImpl);
+};
+
+GpuImageDecodeController::DecodedImageData::DecodedImageData()
+    : ref_count(0), is_locked(false) {}
+
+GpuImageDecodeController::DecodedImageData::~DecodedImageData() = default;
+
+GpuImageDecodeController::UploadedImageData::UploadedImageData()
+    : pending(false), ref_count(0) {}
+
+GpuImageDecodeController::UploadedImageData::~UploadedImageData() = default;
+
+GpuImageDecodeController::ImageData::ImageData(DecodedDataMode mode,
+                                               size_t size)
+    : mode(mode), size(size), is_at_raster(false) {}
+
+GpuImageDecodeController::ImageData::~ImageData() = default;
+
+GpuImageDecodeController::GpuImageDecodeController(ContextProvider* context,
+                                                   ResourceFormat decode_format)
+    : format_(decode_format),
+      context_(context),
+      context_threadsafe_proxy_(context->GrContext()->threadSafeProxy()),
+      image_data_(ImageDataMRUCache::NO_AUTO_EVICT),
+      cached_items_limit_(kMaxDiscardableItems),
+      cached_bytes_limit_(kMaxGpuImageBytes),
+      bytes_used_(0) {}
 
 GpuImageDecodeController::~GpuImageDecodeController() {}
 
 bool GpuImageDecodeController::GetTaskForImageAndRef(
-    const DrawImage& image,
+    const DrawImage& draw_image,
     uint64_t prepare_tiles_id,
     scoped_refptr<ImageDecodeTask>* task) {
-  auto image_id = image.image()->uniqueID();
+  if (SkipImage(draw_image)) {
+    *task = nullptr;
+    return false;
+  }
+
   base::AutoLock lock(lock_);
-  if (prerolled_images_.count(image_id) != 0) {
+  const auto image_id = draw_image.image()->uniqueID();
+
+  auto found = image_data_.Get(image_id);
+  if (found != image_data_.end() && found->second->upload.image) {
+    // The image is already uploaded. If it is not at-raster, or if it will now
+    // fit in the cache (can be converted to not at-raster) ref and return.
+    if (!found->second->is_at_raster ||
+        EnsureCapacityWithClassLock(found->second->size)) {
+      found->second->is_at_raster = false;
+      RefImageWithClassLock(draw_image);
+      *task = nullptr;
+      return true;
+    }
+
+    // Image is at-raster and doesn't fit in the cache. Keep using the image as
+    // at-raster.
     *task = nullptr;
     return false;
   }
 
+  // We didn't have a pre-uploaded image. Try to find an existing upload task.
   scoped_refptr<ImageDecodeTask>& existing_task =
-      pending_image_tasks_[image_id];
-  if (!existing_task) {
-    existing_task = make_scoped_refptr(
-        new ImageDecodeTaskImpl(this, image, prepare_tiles_id));
+      pending_image_upload_tasks_[image_id];
+  if (existing_task) {
+    // We had an existing upload task, ref to the image and return the task.

[vmpstr, 2016/03/28 23:55:53]

either "add ref to the image" or "ref the image"

[ericrk, 2016/03/29 23:11:30]

Done.

+    RefImageWithClassLock(draw_image);
+    *task = existing_task;
+    return true;
+  }
+
+  // We will be creating a new upload task. If necessary, create a placeholder
+  // ImageData to hold the result.
+  scoped_ptr<ImageData> new_data;
+  ImageData* data;
+  if (found == image_data_.end()) {
+    new_data = CreateImageData(draw_image);
+    data = new_data.get();
+  } else {
+    data = found->second.get();
   }
+
+  // Ensure that the image we're about to decode/upload will fit in memory.
+  // Otherwise do an at-raster decode.
+  if (!EnsureCapacityWithClassLock(data->size)) {
+    *task = nullptr;
+    return false;
+  }
+
+  // If we had to create new image data, add it to our map now that we know it
+  // will fit.
+  if (new_data)
+    found = image_data_.Put(image_id, std::move(new_data));
+
+  // Increment |bytes_used_| to reserve room for the pending image. As there is
+  // no |image| created yet, mark the data as |pending|. This lets us account
+  // for the image's size correctly if we cancel this task before uploading.
+  DCHECK(!data->upload.pending);
+  bytes_used_ += data->size;

[vmpstr, 2016/03/28 23:55:53]

There's some extremely rare but possible overflow here. I'm not sure if we
should care or not, but if we should then we have a bunch of checked math
classes in base. 

[ericrk, 2016/03/29 23:11:30]

Updated CanFitSize to use checked math. Now that at-raster is not added to
bytes_used_, we gate all additions by CanFitSize, so we shouldn't have any
issues.

+  data->upload.pending = true;
+
+  // Ref image and create an upload task. We will release this ref in

[vmpstr, 2016/03/28 23:55:52]

nit: create both upload and decode tasks.

[ericrk, 2016/03/29 23:11:30]

Done.

+  // UploadTaskCompleted.
+  RefImageWithClassLock(draw_image);
+  existing_task = make_scoped_refptr(new ImageUploadTaskImpl(
+      this, draw_image,
+      GetImageDecodeTaskAndRefWithClassLock(draw_image, prepare_tiles_id),
+      prepare_tiles_id));
+
+  RefImageWithClassLock(draw_image);

[vmpstr, 2016/03/28 23:55:52]

There's two Refs here (lines 240 and 246). Is that intentional? If so, why? 

Is this for the case that raster is cancelled but the decode task is already
running? Maybe we should do something like this for software as well. In
software, the decode function double checks the ref. 

Either that or gpu should do something like software does. Wdyt?

[ericrk, 2016/03/29 23:11:30]

This was intentional - one ref is kept alive by this class, for the lifetime of
the decode/upload task. The other is the ref that's "returned" to the caller...
Adding a comment.

Keeping a ref alive simplifies the logic in a few places - I could see making SW
behave like this, although I think it's strictly worse, just a little easier to
reason about. Not sure if we want to go down that route.

If you'd like to not take these extra refs in GPU, I could see doing that as
well.. but I'd like to do it in a follow-up, as it adds a number of additional
checks (and there's also some interactions between the decode/upload tasks that
make it a bit annoying).

   *task = existing_task;
-  return false;
+  return true;
 }
 
-void GpuImageDecodeController::UnrefImage(const DrawImage& image) {
-  NOTREACHED();
+void GpuImageDecodeController::UnrefImage(const DrawImage& draw_image) {
+  base::AutoLock lock(lock_);
+  UnrefImageWithClassLock(draw_image);
 }
 
 DecodedDrawImage GpuImageDecodeController::GetDecodedImageForDraw(
     const DrawImage& draw_image) {
-  return DecodedDrawImage(draw_image.image(), draw_image.filter_quality());
+  TRACE_EVENT0("cc", "GpuImageDecodeController::GetDecodedImageForDraw");
+  if (SkipImage(draw_image))
+    return DecodedDrawImage(nullptr, draw_image.filter_quality());
+
+  // We are being called during raster. The context lock must already be
+  // acquired by the caller.
+  context_->GetLock()->AssertAcquired();

[vmpstr, 2016/03/28 23:55:52]

Since we have public functions that need context lock to be acquired already,
I'm wondering if we should rethink the whole name it with lock in the name and
just assert things at the top of the function if they lock is already required
and document it via comments. 

[ericrk, 2016/03/29 23:11:29]

I agree.

+  base::AutoLock lock(lock_);
+
+  const uint32_t unique_id = draw_image.image()->uniqueID();
+  auto found = image_data_.Peek(unique_id);
+  if (found == image_data_.end()) {
+    // We didn't find the image, we are doing at-raster decode.

[vmpstr, 2016/03/28 23:55:53]

Is it possible that the raster task started running, but the rest of the image
raster tasks were cancelled, which allowed us to get under the memory limit? I
don't mind if we still mark this as at-raster, but I think the DCHECK below
might fail in those cases.

[ericrk, 2016/03/29 23:11:29]

Going to just always assume at-raster here.

+    auto data = CreateImageData(draw_image);
+    data->is_at_raster = true;
+    DCHECK(!EnsureCapacityWithClassLock(data->size));

[vmpstr, 2016/03/28 23:55:52]

I'm not sure if I asked you to add this, but since this function has a side
effect of freeing memory I don't think we should put it in a DCHECK (since it
would run in debug but not in release). Maybe just check !CanFitSize ||
!CanFitCount

[ericrk, 2016/03/29 23:11:30]

Removed this, it works fine either way. We can investigate adding this in later.

+
+    // Increment |bytes_used_| to reserve room for the pending image. As there
+    // is no |image| created yet, mark the data as |pending|.
+    bytes_used_ += data->size;

[vmpstr, 2016/03/28 23:55:53]

This is a little bit questionable for me. If this is at raster, then why is it
counting against the memory limit? That is, if I get one really large at-raster
image, then during the next schedule all of the smaller tasks would be at-raster
as well as long as this one is still pending.

That seems non-ideal to me, especially if we create and ref tasks before
scheduling and cancelling the previous work. This might lead to a continuous at
raster schedule or just some bad behavior. 


Also, if it's currently being used and is at raster, then accounting for memory
prevents the conversion to not-at-raster in GetTaskForImageAndRef (since it
would check if we can fit another |size| bytes work of memory). 

[ericrk, 2016/03/29 23:11:30]

Ah, fair point... I think a lot of stuff gets easier if we make at-raster not
budgeted. Updating this.

+    data->upload.pending = true;
+
+    found = image_data_.Put(unique_id, std::move(data));
+  }
+
+  // Ref the image and decode so that they stay alive while we are
+  // decoding/uploading.
+  RefImageWithClassLock(draw_image);
+  RefImageDecodeWithClassLock(draw_image);
+
+  // We may or may not need to decode and upload the image we've found, the
+  // following functions early-out to if we already decoded.
+  DecodeImageIfNecessaryWithClassLock(draw_image, found->second.get());
+  UploadImageIfNecessaryWithClassAndContextLock(draw_image,
+                                                found->second.get());
+  // Unref the image decode, but not the image. The image ref will be released
+  // in DrawWithImageFinished.
+  UnrefImageDecodeWithClassLock(draw_image);
+
+  SkImage* image = found->second->upload.image.get();
+  DCHECK(image);
+
+  DecodedDrawImage decoded_draw_image(image, draw_image.filter_quality());
+  decoded_draw_image.set_at_raster_decode(found->second->is_at_raster);
+  return decoded_draw_image;
 }
 
 void GpuImageDecodeController::DrawWithImageFinished(
-    const DrawImage& image,
-    const DecodedDrawImage& decoded_image) {}
+    const DrawImage& draw_image,
+    const DecodedDrawImage& decoded_draw_image) {
+  if (SkipImage(draw_image))
+    return;
 
-void GpuImageDecodeController::ReduceCacheUsage() {}
+  base::AutoLock lock(lock_);
+  UnrefImageWithClassLock(draw_image);
+
+  // We are mid-draw and holding the context lock, ensure we clean up any
+  // textures (especially at-raster), which may have just been marked for
+  // deletion by UnrefImage.
+  DeletePendingImagesWithClassAndContextLock();
+}
 
-void GpuImageDecodeController::DecodeImage(const DrawImage& image) {
-  image.image()->preroll();
+void GpuImageDecodeController::ReduceCacheUsage() {
   base::AutoLock lock(lock_);
-  prerolled_images_.insert(image.image()->uniqueID());
+  EnsureCapacityWithClassLock(0);
 }
 
-void GpuImageDecodeController::RemovePendingTaskForImage(
-    const DrawImage& image) {
+void GpuImageDecodeController::DecodeImage(const DrawImage& draw_image) {
   base::AutoLock lock(lock_);
-  pending_image_tasks_.erase(image.image()->uniqueID());
+  auto found = image_data_.Peek(draw_image.image()->uniqueID());
+  DCHECK(found != image_data_.end());
+  DCHECK(!found->second->is_at_raster);
+  DecodeImageIfNecessaryWithClassLock(draw_image, found->second.get());
+}
+
+void GpuImageDecodeController::UploadImage(const DrawImage& draw_image) {
+  ContextProvider::ScopedContextLock context_lock(context_);
+  base::AutoLock lock(lock_);
+  auto found = image_data_.Peek(draw_image.image()->uniqueID());
+  DCHECK(found != image_data_.end());
+  DCHECK(!found->second->is_at_raster);
+
+  UploadImageIfNecessaryWithClassAndContextLock(draw_image,
+                                                found->second.get());
+}
+
+void GpuImageDecodeController::DecodeTaskCompleted(
+    const DrawImage& draw_image) {
+  base::AutoLock lock(lock_);
+  // Decode task is complete, remove it from our list of pending tasks.
+  pending_image_decode_tasks_.erase(draw_image.image()->uniqueID());
+
+  // While the decode task is active, we keep a ref on the decoded data.
+  // Release that ref now that the decode is completed.
+  UnrefImageDecodeWithClassLock(draw_image);
+}
+
+void GpuImageDecodeController::UploadTaskCompleted(
+    const DrawImage& draw_image) {
+  base::AutoLock lock(lock_);
+  const uint32_t image_id = draw_image.image()->uniqueID();
+  // Upload task is complete, remove it from our list of pending tasks.
+  pending_image_upload_tasks_.erase(image_id);
+
+  // If the image was never uploaded (|pending| is true), we need to subtract
+  // the pending bytes.

[vmpstr, 2016/03/28 23:55:52]

Otherwise, I guess the bytes are still accounted for in the fact that there's
now a new image in the cache?

[ericrk, 2016/03/29 23:11:30]

Moved all memory tracking to RefCountChanged/EnsureCapacity

+  auto found = image_data_.Peek(image_id);
+  DCHECK(found != image_data_.end());
+  if (found->second->upload.pending) {
+    bytes_used_ -= found->second->size;
+    found->second->upload.pending = false;
+  }
+
+  // While the upload task is active, we keep a ref on both the image it will be
+  // populating, as well as the decode it needs to populate it. Release these
+  // refs now.
+  UnrefImageDecodeWithClassLock(draw_image);
+  UnrefImageWithClassLock(draw_image);
+}
+
+// Checks if an existing image decode exists. If not, returns a task to produce

[vmpstr, 2016/03/28 23:55:53]

I guess normally it's not possible that we're trying to create this while we
didn't have the upload task. However, the upload could have been cancelled and
this one was already running?

[ericrk, 2016/03/29 23:11:30]

We create this when we create the upload task - so I think there should be no
issues. We'd never just create this.

+// the requested decode.
+scoped_refptr<ImageDecodeTask>
+GpuImageDecodeController::GetImageDecodeTaskAndRefWithClassLock(
+    const DrawImage& draw_image,
+    uint64_t prepare_tiles_id) {
+  lock_.AssertAcquired();
+  uint32_t image_id = draw_image.image()->uniqueID();
+  // This ref is kept alive while an upload task may need this decode. We
+  // release this ref in UploadTaskCompleted.
+  RefImageDecodeWithClassLock(draw_image);
+
+  auto found = image_data_.Peek(image_id);
+  if (found != image_data_.end() && found->second->decode.is_locked) {
+    // We should never be creating a decode task for an at raster image.
+    DCHECK(!found->second->is_at_raster);
+    // We should never be creating a decode for an already-uploaded image.
+    DCHECK(!found->second->upload.image);
+    return nullptr;
+  }
+
+  scoped_refptr<ImageDecodeTask>& existing_task =
+      pending_image_decode_tasks_[image_id];
+  if (!existing_task) {
+    // Ref image and create a decode task. This ref will be released in
+    // DecodeTaskCompleted.
+    RefImageDecodeWithClassLock(draw_image);
+    existing_task = make_scoped_refptr(
+        new ImageDecodeTaskImpl(this, draw_image, prepare_tiles_id));
+  }
+  return existing_task;
+}
+
+void GpuImageDecodeController::RefImageDecodeWithClassLock(
+    const DrawImage& draw_image) {
+  lock_.AssertAcquired();
+  auto found = image_data_.Peek(draw_image.image()->uniqueID());
+  DCHECK(found != image_data_.end());
+  // Sanity-check our ref-count.
+  DCHECK_GE(found->second->decode.ref_count, 0u);
+  ++found->second->decode.ref_count;
+}
+
+void GpuImageDecodeController::UnrefImageDecodeWithClassLock(
+    const DrawImage& draw_image) {
+  lock_.AssertAcquired();
+  auto found = image_data_.Peek(draw_image.image()->uniqueID());
+  DCHECK(found != image_data_.end());
+  DCHECK_GT(found->second->decode.ref_count, 0u);
+  --found->second->decode.ref_count;
+  if (found->second->decode.ref_count == 0) {
+    if (found->second->decode.is_locked) {
+      found->second->decode.is_locked = false;
+      found->second->decode.data->Unlock();
+    }
+    EnsureCapacityWithClassLock(0);
+  }
+}
+
+void GpuImageDecodeController::RefImageWithClassLock(
+    const DrawImage& draw_image) {
+  lock_.AssertAcquired();
+  auto image_id = draw_image.image()->uniqueID();
+  auto found = image_data_.Peek(image_id);
+  DCHECK(found != image_data_.end());
+  ++found->second->upload.ref_count;
+}
+
+void GpuImageDecodeController::UnrefImageWithClassLock(
+    const DrawImage& draw_image) {
+  lock_.AssertAcquired();
+  auto image_id = draw_image.image()->uniqueID();
+  auto found = image_data_.Peek(image_id);
+  DCHECK(found != image_data_.end());
+  DCHECK_GT(found->second->upload.ref_count, 0u);
+  --found->second->upload.ref_count;
+  if (found->second->upload.ref_count == 0) {
+    // If the ref count has reached 0, the image should no longer be pending.
+    DCHECK(!found->second->upload.pending);
+
+    // If this image was created as at-raster, it may now fit into the cache.
+    // If so, we'd like to convert it to non-at-raster. Otherwise we'd like to
+    // delete the image.
+    //
+    // We can handle both cases by converting the image into non-at-raster and
+    // then calling EnsureCapacityWithClassLock. If the image now fits,
+    // EnsureCapacityWithClassLock will leave it in the cache, otherwise it
+    // will be removed (independent of the at-raster flag).
+    found->second->is_at_raster = false;
+    EnsureCapacityWithClassLock(0);
+  }
+}
+
+// Ensures that we can fit a new image of size |required_size| in our cache. In
+// doing so, this function will free unreferenced image data as necessary to
+// create rooom.
+bool GpuImageDecodeController::EnsureCapacityWithClassLock(
+    size_t required_size) {
+  lock_.AssertAcquired();
+  const size_t new_elements = required_size ? 1 : 0;
+  if (CanFitSizeWithClassLock(required_size) &&
+      CanFitCountWithClassLock(new_elements))
+    return true;
+
+  // While we are over memory or item capacity, we iterate through our set of
+  // cached image data in LRU order. For each image, we can do two things:
+  // 1) We can free the uploaded image, reducing the memory usage of the cache
+  // and 2) we can remove the entry entirely, reducing the count of elements in
+  // the cache.
+  for (auto it = image_data_.rbegin(); it != image_data_.rend();) {
+    if (it->second->decode.ref_count != 0 ||
+        it->second->upload.ref_count != 0) {
+      ++it;
+      continue;
+    }
+
+    // Current entry has no refs. Ensure it is not locked or pending.
+    DCHECK(!it->second->decode.is_locked);
+    DCHECK(!it->second->upload.pending);
+
+    // Free the uploaded image if possible.
+    if (it->second->upload.image) {
+      DCHECK_GE(bytes_used_, it->second->size);
+      bytes_used_ -= it->second->size;
+      images_pending_deletion_.push_back(std::move(it->second->upload.image));
+      it->second->upload.image = nullptr;
+    }
+
+    // Free the entire entry if necessary.
+    if (!CanFitCountWithClassLock(new_elements)) {
+      it = image_data_.Erase(it);
+    } else {
+      ++it;
+    }
+
+    if (CanFitSizeWithClassLock(required_size) &&
+        CanFitCountWithClassLock(new_elements))
+      return true;
+  }
+
+  // We couldn't reach a state where we are under our memory / count limits.
+  return false;
+}
+
+bool GpuImageDecodeController::CanFitSizeWithClassLock(size_t size) const {
+  return bytes_used_ + size <= cached_bytes_limit_;

[vmpstr, 2016/03/28 23:55:52]

There's a possible overflow here which would erroneously return true for a size
that's exactly std::numeric_limit<size_t>::max()

I think the given size is computed by Skia, so I'm not sure if it can ever
return something like that...

[ericrk, 2016/03/29 23:11:30]

Added safe math. This function is used to gate all cache entry additions, so
safe math shouldn't be necessary other places.

+}
+
+bool GpuImageDecodeController::CanFitCountWithClassLock(
+    size_t num_elements) const {
+  return image_data_.size() + num_elements <= cached_items_limit_;
+}
+
+void GpuImageDecodeController::DecodeImageIfNecessaryWithClassLock(
+    const DrawImage& draw_image,
+    ImageData* image_data) {
+  lock_.AssertAcquired();
+
+  if (image_data->upload.image) {
+    // We already have an uploaded image, no reason to decode.
+    return;
+  }
+
+  if (image_data->decode.data &&
+      (image_data->decode.is_locked || image_data->decode.data->Lock())) {
+    // We already decoded this, or we just needed to lock, early out.
+    image_data->decode.is_locked = true;
+    return;
+  }
+
+  TRACE_EVENT0("cc", "GpuImageDecodeController::DecodeImage");
+  DCHECK_GT(image_data->decode.ref_count, 0u);
+
+  image_data->decode.data = nullptr;
+  scoped_ptr<base::DiscardableMemory> backing_memory;
+  {
+    base::AutoUnlock unlock(lock_);
+    switch (image_data->mode) {
+      case DecodedDataMode::CPU: {
+        backing_memory =
+            base::DiscardableMemoryAllocator::GetInstance()
+                ->AllocateLockedDiscardableMemory(image_data->size);
+        SkImageInfo image_info = CreateImageInfoForDrawImage(draw_image);
+        if (!draw_image.image()->readPixels(image_info, backing_memory->data(),
+                                            image_info.minRowBytes(), 0, 0,
+                                            SkImage::kDisallow_CachingHint)) {
+          backing_memory->Unlock();
+          return;
+        }
+        break;
+      }
+      case DecodedDataMode::GPU: {
+        backing_memory =
+            base::DiscardableMemoryAllocator::GetInstance()
+                ->AllocateLockedDiscardableMemory(image_data->size);
+        auto params = ParamsFromDrawImage(draw_image);
+        if (!draw_image.image()->getDeferredTextureImageData(
+                *context_threadsafe_proxy_, &params, 1,
+                backing_memory->data())) {
+          backing_memory->Unlock();
+          return;
+        }
+        break;
+      }
+    }
+  }
+
+  if (!image_data->decode.data) {

[vmiura, 2016/03/29 01:33:17]

Can this be unconditional, since image_data->decode.data is reset above?

[ericrk, 2016/03/29 23:11:30]

Not in this case, as we unlock during the actual decode, and another task could
have come in and modified this. Added a comment.

+    image_data->decode.data = std::move(backing_memory);
+    DCHECK(!image_data->decode.is_locked);
+    image_data->decode.is_locked = true;
+  }
+}
+
+void GpuImageDecodeController::UploadImageIfNecessaryWithClassAndContextLock(
+    const DrawImage& draw_image,
+    ImageData* image_data) {
+  context_->GetLock()->AssertAcquired();
+  lock_.AssertAcquired();
+
+  if (image_data->upload.image) {
+    // Someone has uploaded this image before us (at raster).
+    return;
+  }
+
+  TRACE_EVENT0("cc", "GpuImageDecodeController::UploadImage");
+  DCHECK(image_data->decode.is_locked);
+  DCHECK_GT(image_data->decode.ref_count, 0u);
+  DCHECK_GT(image_data->upload.ref_count, 0u);
+
+  // We are about to upload a new image and are holding the context lock.
+  // Ensure that any images which have been marked for deletion are actually
+  // cleaned up so we don't exceed our memory limit during this upload.
+  DeletePendingImagesWithClassAndContextLock();
+
+  skia::RefPtr<SkImage> uploaded_image;
+  {
+    base::AutoUnlock unlock(lock_);
+    switch (image_data->mode) {
+      case DecodedDataMode::CPU: {
+        SkImageInfo image_info = CreateImageInfoForDrawImage(draw_image);
+        uploaded_image = skia::AdoptRef(SkImage::NewFromRaster(
+            image_info, image_data->decode.data->data(),
+            image_info.minRowBytes(), [](const void*, void*) {}, nullptr));
+        break;
+      }
+      case DecodedDataMode::GPU: {
+        uploaded_image =
+            skia::AdoptRef(SkImage::NewFromDeferredTextureImageData(
+                context_->GrContext(), image_data->decode.data->data(),
+                SkBudgeted::kNo));
+        break;
+      }
+    }
+  }
+  DCHECK(uploaded_image);
+
+  // At-raster may have decoded this while we were unlocked. If so, ignore our
+  // result.
+  if (!image_data->upload.image) {
+    image_data->upload.image = std::move(uploaded_image);
+    DCHECK(image_data->upload.pending);
+    image_data->upload.pending = false;
+  }
+}
+
+scoped_ptr<GpuImageDecodeController::ImageData>
+GpuImageDecodeController::CreateImageData(const DrawImage& draw_image) {
+  DecodedDataMode mode;
+  SkImageInfo info = CreateImageInfoForDrawImage(draw_image);
+  SkImage::DeferredTextureImageUsageParams params =
+      ParamsFromDrawImage(draw_image);
+  size_t data_size = draw_image.image()->getDeferredTextureImageData(
+      *context_threadsafe_proxy_, &params, 1, nullptr);
+
+  if (data_size == 0) {
+    // Can't upload image, too large or other failure. Try to use SW fallback.
+    data_size = info.getSafeSize(info.minRowBytes());
+    mode = DecodedDataMode::CPU;
+  } else {
+    mode = DecodedDataMode::GPU;
+  }
+
+  return make_scoped_ptr(new ImageData(mode, data_size));
+}
+
+void GpuImageDecodeController::DeletePendingImagesWithClassAndContextLock() {
+  context_->GetLock()->AssertAcquired();
+  lock_.AssertAcquired();
+  images_pending_deletion_.clear();
+}
+
+SkImageInfo GpuImageDecodeController::CreateImageInfoForDrawImage(
+    const DrawImage& draw_image) const {
+  return SkImageInfo::Make(
+      draw_image.image()->width(), draw_image.image()->height(),
+      ResourceFormatToClosestSkColorType(format_), kPremul_SkAlphaType);
 }
 
 }  // namespace cc