fix: Android headless JS timeout

[marcesengel]

Summary

Fixes #33043 and thereby invertase/react-native-firebase#3955.

The issue arised because when there currently is no available React context, HeadlessJsTaskService will create a new one in background and start the task using onReactContextInitialized of ReactInstanceManager.addReactInstanceEventListener.

react-native/ReactAndroid/src/main/java/com/facebook/react/HeadlessJsTaskService.java

Lines 94 to 113 in 7ef14af

	protected void startTask(final HeadlessJsTaskConfig taskConfig) {
	UiThreadUtil.assertOnUiThread();
	acquireWakeLockNow(this);
	final ReactInstanceManager reactInstanceManager =
	getReactNativeHost().getReactInstanceManager();
	ReactContext reactContext = reactInstanceManager.getCurrentReactContext();
	if (reactContext == null) {
	reactInstanceManager.addReactInstanceEventListener(
	new ReactInstanceEventListener() {
	@Override
	public void onReactContextInitialized(ReactContext reactContext) {
	invokeStartTask(reactContext, taskConfig);
	reactInstanceManager.removeReactInstanceEventListener(this);
	}
	});
	reactInstanceManager.createReactContextInBackground();
	} else {
	invokeStartTask(reactContext, taskConfig);
	}
	}

The TimingModule however is initialized asynchronously, meaning the headless JS is started before its initialization. That's an issue because the TimingModule is only run when there is JS code executing (meaning if the application is running or there is a headless task running) - this is checked by registering a HeadlessJsTaskEventListener on the HeadlessJsTaskContext in TimingModule.initialize().

react-native/ReactAndroid/src/main/java/com/facebook/react/modules/core/TimingModule.java

Lines 69 to 75 in 7ef14af

	@Override
	public void initialize() {
	getReactApplicationContext().addLifecycleEventListener(this);
	HeadlessJsTaskContext headlessJsTaskContext =
	HeadlessJsTaskContext.getInstance(getReactApplicationContext());
	headlessJsTaskContext.addTaskEventListener(this);
	}

However this event listener is never invoked because the task was started before TimingModule.initialize() is called -> TimingModule.onHeadlessJsTaskStart(...) is not called and the timer never resumes.

In order to fix this we can just invoke HeadlessJsTaskEventListener.onHeadlessJsTaskStart(...) for all currently running tasks when a new listener is added to HeadlessJsTaskContext. This call then needs to be synchronized as otherwise there's a race condition with HeadlessJsTaskContext.finishTask(...) where onHeadlessJsTaskFinish(...) could be called before onHeadlessJsTaskStart(...). See the diff for the exact changes.

Changelog

[Android] [Fix] - Fixed TimingModule related functions for headless JS tasks, eg. setTimeout

Test Plan

I did a local build with the changes and tested the provided example code from #33043 there.

[mikehardy]

This looks good to me, from my experience as a java / android native dev but - importantly - without a lot of experience in the headless JS area of react-native. Nice one @marcesengel

[marcesengel]

Thank you very much for the review and the kind words @mikehardy! Do you have any insights on how to get this merged? I currently have 3 open PRs going with the oldest being from over 3 weeks ago and no feedback yet 😕

[mikehardy]

No special tricks other than making some noise, metaphorically. You can use git commit history to find last committer (or recent frequent committer) for the file and tag them. I can try to get attention from the release crew. Can you add a link to your other 2 PRs here?

[marcesengel]

Thank you very much, will do. The PRs in question are #32889/#33045 (the same changes, the original one has a comment and points to 0.66-stable and the second one points to main, as the first one didn't receive the tag "shared with react-native team") and #32863.

Thanks again for your help, much appreciated 👍

[facebook-github-bot]

@dmitryrykun has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[jspizziri]

Would love to see this get fixed.

[react-native-bot]

This pull request was successfully merged by @marcesengel in dac56ce.

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