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During image decoding, avoid using smart pointers for DartWrappables that cross thread-boundaries. #23503
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…that cross thread-boundaries. In flutter#19843, a regression was introduced where an image descriptor object that has a Dart peer could be collected on a concurrent task runner thread. Collection of such object needs to enter isolate scope which might still be active on the UI thread. [A comment in the original commit explicitly mentions][1] this and attempts to achieve the collection of the Dart wrappable on the UI task runner. However, the author missed that the object was present in the captures of a copyable closure. These captures may be released on any of the participating threads. To avoid the the indeterminism of the smart pointer being dropped on the concurrent task runner thread, this patch resorts to manually reference counting the descriptor. Fixes flutter/flutter#72144 [1]: https://github.com/flutter/engine/pull/19843/files#diff-a3034d4a06133381b6b636d841ec98cb7cfce640f316dda9e71eda4d9e7872f6R227
jason-simmons
approved these changes
Jan 7, 2021
| // `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)
|
Filed a flake report and re-run the presubmit. |
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…ppables that cross thread-boundaries. (flutter/engine#23503)
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Hello, is this in beta at the moment? |
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In #19843, a regression was introduced
where an image descriptor object that has a Dart peer could be collected on a
concurrent task runner thread. Collection of such object needs to enter isolate
scope which might still be active on the UI thread. A comment in the original
commit explicitly mentions this and attempts to achieve the collection of the
Dart wrappable on the UI task runner. However, the author missed that the object
was present in the captures of a copyable closure. These captures may be
released on any of the participating threads. To avoid the the indeterminism of
the smart pointer being dropped on the concurrent task runner thread, this patch
resorts to manually reference counting the descriptor.
Fixes flutter/flutter#72144