We can discard frames from an animated image if the memory footprint
exceeds the threshold. This will cause us to redecode frames on demand
instead. However decoders can fail to produce the same results on
subsequent runs due to differences in memory pressure, etc. If this
happens our state can get inconsistent. In particular, if we keep
failing on the first frame, we end up in an infinite loop on the decoder
thread.
Since we don't have the owning image to signal, as we had to release our
reference to it after the first pass, we can do little but stop decoding.
From the user's perspective, the animation will come to a stop.
We can discard frames from an animated image if the memory footprint
exceeds the threshold. This will cause us to redecode frames on demand
instead. However decoders can fail to produce the same results on
subsequent runs due to differences in memory pressure, etc. If this
happens our state can get inconsistent. In particular, if we keep
failing on the first frame, we end up in an infinite loop on the decoder
thread.
Since we don't have the owning image to signal, as we had to release our
reference to it after the first pass, we can do little but stop decoding.
From the user's perspective, the animation will come to a stop.
When we shutdown the decode pool threads, it does not do a simple join
with the main thread. It will actually process the main thread event
loop, which can cause a bad series of events. The refresh tick could
still be running and advancing our animated images, causing the animated
decoders to continue running, which in turn prevents the decoder threads
from finishing shutting down, and the main thread from joining them.
Now we check on each frame whether or not the decoder should just stop
decoding more frames because the decode pool has started shutdown. If it
has, it will stop immediately.
After decoding the first frame we allocate the second frame, but before it finishes we encounter an error, Decoder::PostError is called it aborts the second frame and decrements the frame count. But AnimationSurfaceProvider::CheckForFrameAtTerminalState just asks for the current frame ref from the decoder (which it never cleared) and inserts that.
The condition that we use from the decoder to decide to report a new frame is mFinishedNewFrame (via TakeCompleteFrameCount), however this doesn't directly correspond to mFrameCount. So we create a new bool on the Decoder to track when there is a frame that we can take.
This didn't cause any problems before but now we have tighter coupling between the list of frames the AnimationSurfaceProvider has and what FrameAnimator expects.
Another possible fix would be to clear the current frame ref in PostError, but the only place we clear the current frame is when we allocate the new frame and we have the mImageData pointer still around that decoders could theorhetically use to do final processing on the last partial frame.
When we need to recreate an animated image decoder because it was
discarded, the animation may have progressed beyond the first frame.
Given that later in the patch series we need FrameAnimator to be driving
the decoding more actively, it simplifies its role by making it assume
the initial state of the decoder matches its initial state. Passing in
the currently displayed frame allows the decoder to advance its frame
buffer (and potentially discard unnecessary frames), such that when the
animation actually wants to advance as it normally would, the decoder
state matches what it would have been if it had never been discarded.
The shared memory handle reporting has been generalized to be an
external handle reporting. This is used for both shared memory, and for
volatile memory (on Android.) This will allow us to have a better sense
of just how many handles are being used by images on Android.
Additionally we were not properly reporting forced heap allocated
memory, if we were putting animated frames on the heap. This is because
we used SourceSurfaceAlignedRawData without implementing
AddSizeOfExcludingThis.
Andrew Osmond
Cosmin Sabou
Timothy Nikkel
Andrew McCreight
Seth Fowler