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During image decoding, avoid using smart pointers for DartWrappables that cross thread-boundaries. #23503

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Jan 9, 2021
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During image decoding, avoid using smart pointers for DartWrappables that cross thread-boundaries. #23503

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77 changes: 47 additions & 30 deletions lib/ui/painting/image_decoder.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,7 @@ static sk_sp<SkImage> ResizeRasterImage(sk_sp<SkImage> image,
}

static sk_sp<SkImage> ImageFromDecompressedData(
fml::RefPtr<ImageDescriptor> descriptor,
ImageDescriptor* descriptor,
uint32_t target_width,
uint32_t target_height,
const fml::tracing::TraceFlow& flow) {
Expand All @@ -98,7 +98,7 @@ static sk_sp<SkImage> ImageFromDecompressedData(
SkISize::Make(target_width, target_height), flow);
}

sk_sp<SkImage> ImageFromCompressedData(fml::RefPtr<ImageDescriptor> descriptor,
sk_sp<SkImage> ImageFromCompressedData(ImageDescriptor* descriptor,
uint32_t target_width,
uint32_t target_height,
const fml::tracing::TraceFlow& flow) {
Expand Down Expand Up @@ -216,38 +216,55 @@ static SkiaGPUObject<SkImage> UploadRasterImage(
return result;
}

void ImageDecoder::Decode(fml::RefPtr<ImageDescriptor> descriptor,
void ImageDecoder::Decode(fml::RefPtr<ImageDescriptor> descriptor_ref_ptr,
uint32_t target_width,
uint32_t target_height,
const ImageResult& callback) {
TRACE_EVENT0("flutter", __FUNCTION__);
fml::tracing::TraceFlow flow(__FUNCTION__);

// ImageDescriptors have Dart peers that must be collected on the UI thread.
// However, closures in MakeCopyable below capture the descriptor. The
// captures of copyable closures may be collected on any of the thread
// participating in task execution.
//
// To avoid this issue, we resort to manually reference counting the
// descriptor. Since all task flows invoke the `result` callback, the raw
// descriptor is retained in the beginning and released in the `result`
// callback.
//
// `ImageDecoder::Decode` itself is invoked on the UI thread, so the
// collection of the smart pointer from which we obtained the raw descriptor
// is fine in this scope.
auto raw_descriptor = descriptor_ref_ptr.get();
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It might be useful to add a method to fml::RefPtr that detaches the raw pointer from the RefPtr and gives the caller ownership of the ref count that was held by the RefPtr.

(similar to std::unique_ptr::release or Skia's sk_sp::release)

raw_descriptor->AddRef();

FML_DCHECK(callback);
FML_DCHECK(runners_.GetUITaskRunner()->RunsTasksOnCurrentThread());

// Always service the callback (and cleanup the descriptor) on the UI thread.
auto result = [callback, descriptor, ui_runner = runners_.GetUITaskRunner()](
SkiaGPUObject<SkImage> image,
fml::tracing::TraceFlow flow) {
ui_runner->PostTask(
fml::MakeCopyable([callback, descriptor, image = std::move(image),
flow = std::move(flow)]() mutable {
// We are going to terminate the trace flow here. Flows cannot
// terminate without a base trace. Add one explicitly.
TRACE_EVENT0("flutter", "ImageDecodeCallback");
flow.End();
callback(std::move(image));
}));
};

if (!descriptor->data() || descriptor->data()->size() == 0) {
auto result =
[callback, raw_descriptor, ui_runner = runners_.GetUITaskRunner()](
SkiaGPUObject<SkImage> image, fml::tracing::TraceFlow flow) {
ui_runner->PostTask(fml::MakeCopyable(
[callback, raw_descriptor, image = std::move(image),
flow = std::move(flow)]() mutable {
// We are going to terminate the trace flow here. Flows cannot
// terminate without a base trace. Add one explicitly.
TRACE_EVENT0("flutter", "ImageDecodeCallback");
flow.End();
callback(std::move(image));
raw_descriptor->Release();
}));
};

if (!raw_descriptor->data() || raw_descriptor->data()->size() == 0) {
result({}, std::move(flow));
return;
}

concurrent_task_runner_->PostTask(
fml::MakeCopyable([descriptor, //
fml::MakeCopyable([raw_descriptor, //
io_manager = io_manager_, //
io_runner = runners_.GetIOTaskRunner(), //
result, //
Expand All @@ -258,16 +275,15 @@ void ImageDecoder::Decode(fml::RefPtr<ImageDescriptor> descriptor,
// Step 1: Decompress the image.
// On Worker.

auto decompressed =
descriptor->is_compressed()
? ImageFromCompressedData(std::move(descriptor), //
target_width, //
target_height, //
flow)
: ImageFromDecompressedData(std::move(descriptor), //
target_width, //
target_height, //
flow);
auto decompressed = raw_descriptor->is_compressed()
? ImageFromCompressedData(raw_descriptor, //
target_width, //
target_height, //
flow)
: ImageFromDecompressedData(raw_descriptor, //
target_width, //
target_height, //
flow);

if (!decompressed) {
FML_LOG(ERROR) << "Could not decompress image.";
Expand All @@ -283,7 +299,8 @@ void ImageDecoder::Decode(fml::RefPtr<ImageDescriptor> descriptor,
std::move(flow)]() mutable {
if (!io_manager) {
FML_LOG(ERROR) << "Could not acquire IO manager.";
return result({}, std::move(flow));
result({}, std::move(flow));
return;
}

// If the IO manager does not have a resource context, the caller
Expand Down
2 changes: 1 addition & 1 deletion lib/ui/painting/image_decoder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ class ImageDecoder {
FML_DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
};

sk_sp<SkImage> ImageFromCompressedData(fml::RefPtr<ImageDescriptor> descriptor,
sk_sp<SkImage> ImageFromCompressedData(ImageDescriptor* descriptor,
uint32_t target_width,
uint32_t target_height,
const fml::tracing::TraceFlow& flow);
Expand Down
12 changes: 6 additions & 6 deletions lib/ui/painting/image_decoder_unittests.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -556,10 +556,10 @@ TEST(ImageDecoderTest, VerifySimpleDecoding) {
auto descriptor =
fml::MakeRefCounted<ImageDescriptor>(std::move(data), std::move(codec));

ASSERT_EQ(
ImageFromCompressedData(descriptor, 6, 2, fml::tracing::TraceFlow(""))
->dimensions(),
SkISize::Make(6, 2));
ASSERT_EQ(ImageFromCompressedData(descriptor.get(), 6, 2,
fml::tracing::TraceFlow(""))
->dimensions(),
SkISize::Make(6, 2));
}

TEST(ImageDecoderTest, VerifySubpixelDecodingPreservesExifOrientation) {
Expand All @@ -574,8 +574,8 @@ TEST(ImageDecoderTest, VerifySubpixelDecodingPreservesExifOrientation) {
ASSERT_EQ(SkISize::Make(600, 200), image->dimensions());

auto decode = [descriptor](uint32_t target_width, uint32_t target_height) {
return ImageFromCompressedData(descriptor, target_width, target_height,
fml::tracing::TraceFlow(""));
return ImageFromCompressedData(descriptor.get(), target_width,
target_height, fml::tracing::TraceFlow(""));
};

auto expected_data = OpenFixtureAsSkData("Horizontal.png");
Expand Down