Fix dead-lock issue attempting to decode

third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 36 matching lines @@
 }
 
 DecodingImageGenerator::~DecodingImageGenerator()
 {
 }
 
 SkData* DecodingImageGenerator::onRefEncodedData(GrContext* ctx)
 {
     TRACE_EVENT0("blink", "DecodingImageGenerator::refEncodedData");
 
-    return m_allDataReceived ? m_data->getAsSkData().leakRef() : nullptr;
+    // The GPU only wants the data if it has all been received, since the GPU
+    // only wants a complete texture. getAsSkData() may require copying, so
+    // skip it and just return nullptr to avoid a slowdown. (See
+    // crbug.com/568016 for details about such a slowdown.)

[f(malita), 2016/06/29 17:38:37]

It seems a bit fragile to tweak this implementation for internal Skia semantics.
 Would it make sense to add a "bool requireCompleteData" param to
onRefEncodedData() at some point?

[reed1, 2016/06/29 17:57:45]

agreed, seems fragile. Can you imagine other ways to address this longer term?
- explicit flags sent to this api?
- diff API reporting if the generator is "complete"?
- other?

[scroggo_chromium, 2016/06/29 19:21:21]

Tracking with a bug: skbug.com/5485

[scroggo_chromium, 2016/06/29 19:21:21]

Agreed. Added a TODO.
Possibly. Prior to reed@'s landing of crrev.com/1970773002, we discussed many
options for how to do this better, and weren't happy with any of them. For the
moment, we decided to remove the call that was inefficient, and bring it back
once it actually gets used.

+    if (ctx && !m_allDataReceived)
+        return nullptr;
+
+    // Other clients are serializers, which want the data even if it requires
+    // copying, and even if the data is incomplete. (Otherwise they would
+    // potentially need to decode the partial image in order to re-encode it.)
+    return m_data->getAsSkData().leakRef();
 }
 
 bool DecodingImageGenerator::onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor table[], int* tableCount)
 {
     TRACE_EVENT1("blink", "DecodingImageGenerator::getPixels", "frame index", static_cast<int>(m_frameIndex));
 
     // Implementation doesn't support scaling yet so make sure we're not given a different size.
     if (info.width() != getInfo().width() || info.height() != getInfo().height())
         return false;
 
@@ skipping 58 matching lines @@
     const SkImageInfo info = SkImageInfo::MakeN32Premul(size.width(), size.height());
 
     RefPtr<ImageFrameGenerator> frame = ImageFrameGenerator::create(SkISize::Make(size.width(), size.height()), false);
     if (!frame)
         return 0;
 
     return new DecodingImageGenerator(frame, info, segmentReader.release(), true, 0);
 }
 
 } // namespace blink