fix(synth): prevent audio thread spin loops and GC storms on playback end#2711
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xyfu66 wants to merge 1 commit into
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fix(synth): prevent audio thread spin loops and GC storms on playback end#2711xyfu66 wants to merge 1 commit into
xyfu66 wants to merge 1 commit into
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… end [Root Cause] When AlphaSynth finishes generating all audio chunks, it previously sent a 0-length Float32Array to the output to signal the end of data. However, on platforms like Android, writing 0 samples to the `AudioTrack` is non-blocking and returns immediately. This causes the audio playback head to freeze (underrun), which in turn makes the native worker report `playedSamples = 0`. Since `_onSamplesPlayed(0)` short-circuits and ignores the update, the `_notPlayedSamples` counter never reaches 0. As a result, AlphaSynth never calls `stop()`, never emits the `playerFinished` event, and the native audio thread falls into an infinite 100% CPU spin loop (allocating massive arrays per second and triggering a severe GC storm). [Solution] Instead of sending a 0-length array when no data is left, we now send an array of silence matching the normal micro-buffer size. This allows the output device to block and consume data naturally, preventing the underrun. Consequently, `_notPlayedSamples` accurately drains to 0, allowing AlphaSynth to properly shut down and emit the `playerFinished` event.
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Issues
Fixes N/A (Discovered this bug while integrating AlphaTab on Android where it caused infinite GC storms).
Proposed changes
Root Cause
When AlphaSynth finishes generating all audio chunks, it previously sent a 0-length Float32Array to the output to signal the end of data. However, on platforms like Android, writing 0 samples to the
AudioTrackis non-blocking and returns immediately.This causes the audio playback head to freeze (underrun), which in turn makes the native worker report
playedSamples = 0.Since
_onSamplesPlayed(0)short-circuits and ignores the update, the_notPlayedSamplescounter never reaches 0. As a result, AlphaSynth never callsstop(), never emits theplayerFinishedevent, and the native audio thread falls into an infinite 100% CPU spin loop (allocating massive arrays per second and triggering a severe GC storm).Solution
Instead of sending a 0-length array when no data is left, we now send an array of silence matching the normal micro-buffer size. This allows the output device to block and consume data naturally, preventing the underrun. Consequently,
_notPlayedSamplesaccurately drains to 0, allowing AlphaSynth to properly shut down and emit theplayerFinishedevent.Checklist
(No tests were added because this is a fix for a platform-specific AudioTrack underrun deadlock that occurs asynchronously between the TS state machine and the Android native UI thread, making it difficult to cover in standard headless unit tests.)
Further details