iOS: infinite mutual recursion in AudioEngine on configuration change → stack overflow (SIGSEGV) — 0.12.2 and 0.13.1

[bjorlov]

Description

When an engine configuration change is handled while sessionDeactivationInvalidatedGraph is set and a tracked graph exists, AudioEngine's startEngine and its rebuild method call each other in unbounded mutual recursion until the thread stack overflows. The app dies with EXC_BAD_ACCESS / KERN_PROTECTION_FAILURE at a stack guard page — the crash report says it outright:

"message": "Thread stack size exceeded due to excessive recursion"
  -[AudioEngine startEngine]
  -[AudioEngine rebuildAudioEngineAndResumeIfNeeded]
  -[AudioEngine startEngine]
  -[AudioEngine rebuildAudioEngineAndResumeIfNeeded]
  ... (alternating for 245 rounds, to the bottom of the stack)

Expected: configuration changes (recorder start/stop, audio route changes) rebuild/restart the engine and playback continues. Actual: the app crashes.

Affected: 0.13.1 (startEngine ↔ rebuildAudioEngineAndResumeIfNeeded) and 0.12.2 (startEngine ↔ restartAudioEngine — same cycle before the refactor). Crash reports for both versions, from a physical iPhone 14 Pro (iOS 18.7.8) and from the iOS 26.2 Simulator, are in the MRE repo: https://github.com/bjorlov/rnaa-recursion-mre/tree/main/crash-reports

Root cause

sessionDeactivationInvalidatedGraph is preserved across rebuilds (destroyAudioEnginePreservingSessionDeactivationState:YES) and is only cleared at the end of a successful startEngine — but startEngine re-enters the rebuild before ever reaching that point:

// AudioEngine.mm — startEngine
if (self.state == AudioEngineState::AudioEngineStateInterrupted || self.graphNeedsRebuild ||
    self.sessionDeactivationInvalidatedGraph) {
  [self rebuildAudioEngineAndResumeIfNeeded];   // ← re-enters before the flag can ever clear
}
...
self.state = AudioEngineState::AudioEngineStateRunning;
self.sessionDeactivationInvalidatedGraph = false; // ← never reached while the loop spins

// AudioEngine.mm — rebuildAudioEngineAndResumeIfNeeded
[self rebuildAudioEngine];   // clears graphNeedsRebuild, PRESERVES the session flag
if (self.state == AudioEngineState::AudioEngineStateRunning) {
  [self startEngine];        // ← sees the still-set flag → recursion
}

Nothing inside the loop can clear the flag, because clearing requires the successful start the loop prevents.

Suggested fix (verified)

Clear the flag once the graph has been rebuilt — the rebuild is the remedy for whatever the deactivation invalidated — plus optionally a re-entrancy guard:

- (void)rebuildAudioEngineAndResumeIfNeeded
{
  static BOOL isRebuilding = NO;
  if (isRebuilding) {
    return;
  }
  isRebuilding = YES;

  if ([self.audioEngine isRunning]) {
    [self.audioEngine stop];
  }

  [self rebuildAudioEngine];
  self.sessionDeactivationInvalidatedGraph = false; // the graph was just rebuilt — nothing is stale

  if (self.state == AudioEngineState::AudioEngineStateRunning) {
    [self startEngine];
  }

  isRebuilding = NO;
}

We run this as a local patch on 0.13.1 in our app (a guitar tuner: AudioContext playback + AudioRecorder + session category switching); the previously 100%-reproducible crash is gone under the same torture testing. In the real app the most reliable trigger was Bluetooth (A2DP) headphones: with playAndRecord+defaultToSpeaker ↔ playback category switching, every switch is also a hardware route change, and the app crashed on nearly every tuner-screen ↔ playback-screen navigation. The MRE proves Bluetooth is not required, though — recorder start/stop + category churn alone reaches the same path.

Steps to reproduce

1. Clone https://github.com/bjorlov/rnaa-recursion-mre — one screen, react-native-audio-api 0.13.1 pinned: an oscillator beep (tracked source node) while a loop starts/stops the AudioRecorder and flips the audio session between playAndRecord(+defaultToSpeaker) and playback.
2. npm install && npx expo run:ios — the iOS Simulator is enough, no hardware needed.
3. Tap Start torture.
4. The app dies with SIGSEGV within seconds (usually 2-4 cycles). The crash report shows the alternating startEngine / rebuildAudioEngineAndResumeIfNeeded frames with "Thread stack size exceeded due to excessive recursion".

Snack or a link to a repository

https://github.com/bjorlov/rnaa-recursion-mre

React Native Audio API version

0.13.1 (0.12.2 also affected — see description)

React Native version

0.86.0

Platforms

iOS

JavaScript runtime

Hermes

Workflow

Expo Dev Client

Architecture

Fabric (New Architecture)

Build type

Debug app & dev bundle

Device

Real device

Device model

iPhone 17 Pro Simulator (iOS 26.2); also iPhone 14 Pro (iOS 18.7.8)

Acknowledgements

Yes

[mdydek]

just released 0.13.2 with fix for this issue