v0.9.2 - Bluetooth Deadlock Resilience

Improves Bluetooth deadlock resilience with a targeted fix based on spindump evidence from a live deadlock capture.

Root cause (refined)

v0.9.1 dispatched stopRunning() to a background thread to avoid blocking the main thread during Bluetooth teardown. This worked, but the leaked background thread still held a CMIO semaphore that coreaudiod was waiting on, creating a circular deadlock chain:

1. coreaudiod IO thread stuck in HALB_Guard::WaitFor() on dead Bluetooth device (96% of spindump samples)
2. BTAudioHALPlugin blocked by mutex held by stuck IO thread
3. coreaudiod AudioDeviceManager blocked by CMIO semaphore owned by mic-warm
4. mic-warm's CMIO thread blocked waiting for coreaudiod to complete teardown

Fixes

• CMIO pipeline teardown: removeInput() / removeOutput() called on the main thread before dispatching stopRunning() to background, releasing the semaphore coreaudiod blocks on. Measured teardown at 30-44ms with no deadlock (vs potentially hanging forever)
• Stale delegate cleanup: old session's setSampleBufferDelegate(nil, queue: nil) called during teardown to prevent stale callbacks from corrupting new session's sample count
• Thread-safe logging: replaced DateFormatter with ISO8601DateFormatter (thread-safe by design) to prevent crashes from concurrent logging across main and background threads

Docs

• README updated: describes both delay triggers (hardware sleep after ~60s idle AND Bluetooth device switching regardless of idle state), documents deadlock resilience approach
• Apple Feedback draft updated: includes precise spindump call stack evidence and kTCCServiceAudioCapture finding on macOS 26.2

Full Changelog: v0.9.1...v0.9.2

v0.9.1 - Bluetooth Deadlock Fix

Fixes a deadlock that caused mic-warm to freeze when Bluetooth audio devices (AirPods, etc.) disconnect.

Root cause

When AirPods disconnect while mic-warm is running, the debounced restart calls AVCaptureSession.stopRunning() on the old session. CoreAudio hangs in AudioObjectRemovePropertyListener waiting on a condition variable for the now-dead Bluetooth device. The main thread blocks forever, mic goes cold, and push-to-talk gets the activation delay again.

Fixes

• Bluetooth deadlock fix: stopRunning() dispatched to a background thread so a hung Bluetooth teardown is a leaked thread, not a dead process
• Auto-recovery: heartbeat timer detects stalled streams (>15s no samples) or zero-sample sessions (>30s) and automatically restarts the capture session
• Signal handler safety: removed stopRunning() from SIGTERM/SIGINT handler to prevent deadlock on shutdown
• Data race fix: sample counting moved to main queue to prevent race between audio callback and heartbeat
• KVO crash fix: removeObserver guard matched to addObserver to prevent crash on session restart
• Watchdog: logs warning if background stopRunning() hangs for >10s (observability for the Bluetooth deadlock)
• DateFormatter thread safety: replaced DateFormatter with thread-safe ISO8601DateFormatter to prevent crashes from concurrent logging across main and background threads
• Stale delegate fix: old session's sample buffer delegate is nil'd before dispatching stopRunning() to prevent stale callbacks from corrupting new session's sample count

Instrumentation

All diagnostic code (per-device CoreAudio listeners, AVFoundation session lifecycle notifications, verbose heartbeat logging) is retained behind #if false blocks for future debugging. Zero runtime cost.

Full Changelog: v0.9.0...v0.9.1

v0.9.0 - Native Swift Binary

Replaces ffmpeg + SwitchAudioSource with a single native Swift binary. No Homebrew dependencies.

Why this release

Homebrew upgrades move ffmpeg to a new versioned path (e.g. 8.0.1_2 to 8.0.1_3). macOS TCC tracks mic permissions by binary path for unsigned binaries, so every brew upgrade silently breaks the mic permission. The native binary at ~/.local/bin/mic-warm with ad-hoc code signing provides a stable identity that persists across updates.

What's new

• Native Swift binary using AVCaptureSession to hold the mic open (replaces ffmpeg)
• Event-driven device detection via CoreAudio property listener (replaces SwitchAudioSource polling)
• Universal binary (ARM + Intel) built and released automatically via GitHub Actions
• One-line install: curl -fsSL https://raw.githubusercontent.com/drewburchfield/macos-mic-keepwarm/master/install.sh | bash
• Automatic migration from the old ffmpeg-based method
• Signal-safe shutdown on SIGTERM/SIGINT with PID file cleanup
• Recovery loop handles coreaudiod restarts and missing audio devices

What's removed

• No more Homebrew dependency
• No more ffmpeg or SwitchAudioSource requirements
• No more PATH-dependent LaunchAgent configuration

Install

curl -fsSL https://raw.githubusercontent.com/drewburchfield/macos-mic-keepwarm/master/install.sh | bash

Uninstall

curl -fsSL https://raw.githubusercontent.com/drewburchfield/macos-mic-keepwarm/master/uninstall.sh | bash

Compatibility

• macOS 13 Ventura through macOS 26 Tahoe
• Apple Silicon and Intel Macs

v0.2.0 - Device Change Debouncing

What's new

• Debounced device-change detection: 3-second settle window prevents rapid restarts when Bluetooth devices (AirPods, headsets) are connecting. macOS often fires multiple device-change events during a Bluetooth handoff; the debounce waits for things to settle before restarting the audio stream.
• Integration test suite: Automated tests for process lifecycle, signal handling, and device switching.

Requirements

• Homebrew, ffmpeg, SwitchAudioSource (same as v0.1.0)

v0.1.0 - Initial Release

Initial release of macos-mic-keepwarm.

What it does

Keeps the macOS microphone hardware warm to eliminate the 2-5 second push-to-talk activation delay on Apple Silicon Macs.

Implementation

• Shell script (keep-mic-warm.sh) using ffmpeg to hold the mic input stream open
• SwitchAudioSource for device detection
• LaunchAgent for automatic startup
• PID file management for clean process lifecycle

Requirements

• Homebrew
• ffmpeg (brew install ffmpeg)
• SwitchAudioSource (brew install switchaudio-osx)