[Android] Timers do not run when using HeadlessJsTaskService

[gmanole01]

Description

Hello!

I noticed that when using HeadlessJsTaskService, the timers do not run as expected. I did some investigations and I found out that React Native uses Android's Choreographer to schedule the timers.
I am testing the app on a real device: Samsung Galaxy S22 Ultra.
Apparently, Samsung's OneUI pauses the Choreographer when the app goes into background.
In order to fix this, React Native should use another technique to get "ticks", like a Handler or something, at least for the timers (I saw UI events are also processed using Choreographer).

Steps to reproduce

1. Install the application using "yarn android"
2. Open up Android Studio with Logcat open
3. Wait for the background service to start
4. Put the app in foreground by going on the home screen
5. Look in the logs and wait for the line with "CoreRune.SYSPERF_ACTIVE_APP_BBA_ENABLE : stop animation in background states"

React Native Version

0.84.1

Affected Platforms

Runtime - Android

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.3.1
  CPU: (14) arm64 Apple M3 Max
  Memory: 160.17 MB / 36.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.13.1
    path: /Users/george/.nvm/versions/node/v22.13.1/bin/node
  Yarn:
    version: 3.6.4
    path: /Users/george/.nvm/versions/node/v22.13.1/bin/yarn
  npm:
    version: 10.9.2
    path: /Users/george/.nvm/versions/node/v22.13.1/bin/npm
  Watchman:
    version: 2025.05.26.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/george/.rvm/gems/ruby-3.0.0/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.0
      - iOS 26.0
      - macOS 26.0
      - tvOS 26.0
      - visionOS 26.0
      - watchOS 26.0
  Android SDK:
    API Levels:
      - "30"
      - "31"
      - "33"
      - "34"
      - "35"
      - "36"
      - "36"
    Build Tools:
      - 30.0.2
      - 30.0.3
      - 33.0.0
      - 34.0.0
      - 35.0.0
      - 36.0.0
      - 36.0.0
    System Images:
      - android-34 | Android TV ARM 64 v8a
      - android-35 | ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
      - android-35 | Google Play Tablet ARM 64 v8a
      - android-36 | Google Play ARM 64 v8a
      - android-36 | Pre-Release 16 KB Page Size Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2025.3 AI-253.30387.90.2532.14935130
  Xcode:
    version: 26.0.1/17A400
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.0.0
    path: /Users/george/.rvm/rubies/ruby-3.0.0/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.84.1
    wanted: 0.84.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

2026-04-04 17:31:59.258 11074-11128 ReactNativeJS           com.choreographerissue               I  Hello from service!
2026-04-04 17:32:00.260 11074-11128 ReactNativeJS           com.choreographerissue               I  Hello from service!
2026-04-04 17:32:01.264 11074-11128 ReactNativeJS           com.choreographerissue               I  Hello from service!
2026-04-04 17:32:02.267 11074-11128 ReactNativeJS           com.choreographerissue               I  Hello from service!
2026-04-04 17:32:02.526 11074-11074 Choreographer           com.choreographerissue               D  CoreRune.SYSPERF_ACTIVE_APP_BBA_ENABLE : stop animation in background states

MANDATORY Reproducer

https://github.com/gmanole01/react-native-choreographer-issue

Screenshots and Videos

No response

[pranjal2410719]

Thanks for the detailed report and investigation — this is a great find.

However, the issue is slightly deeper than just Samsung pausing Choreographer.

🔍 Root cause

React Native timers (via TimingModule) are currently driven by ReactChoreographer, which ultimately relies on Android’s Choreographer (vsync / UI frame callbacks).

This creates a hidden assumption:

JS timers are tied to the UI rendering loop

That works fine in foreground apps, but breaks in background/headless scenarios.

On devices like Samsung (OneUI), Choreographer is explicitly paused when the app goes to background (as seen in the logs), which means:

• No frame callbacks
• No timer ticks
• JS timers stop executing

So the real issue is:

Timers in React Native depend on a UI-driven scheduling mechanism, even when running in Headless JS (which has no UI).

---

⚠️ Why this is problematic

Headless JS is designed for background execution, but:

• It still depends on a UI-bound scheduler
• Behavior becomes OEM-dependent (Samsung exposes it clearly, but other vendors may also throttle frames)

This makes timers unreliable in any background execution context.

---

💡 Suggested fix (for React Native)

React Native should decouple timer scheduling from Choreographer in non-UI contexts.

A possible approach:

• Use Choreographer only when the app is in foreground / UI is active
• Fall back to a background-safe scheduler when running headless, such as:
  • Handler.postDelayed
  • ScheduledExecutorService

In other words, a dual scheduling strategy:

Context	Scheduler
Foreground (UI active)	Choreographer
Background / Headless JS	Handler / Executor

This would:

• Make timers reliable in Headless JS
• Remove OEM-specific behavior differences
• Align with expectations of background services on Android

---

🧪 Workarounds (for others hitting this)

• Avoid relying on JS timers in Headless JS tasks
• Use Android-native scheduling (WorkManager, AlarmManager, or a foreground service)
• Or implement timing logic in a native module

---

📌 Summary

This is not just a Samsung-specific issue — it reveals a design limitation in how React Native schedules timers. Fixing it would improve reliability of background execution across all Android devices.