Preserve lazy ViewManager initialization in UIManager

[fairysword]

Summary:

• Preserve lazy ViewManager property descriptors when composing UIManager.
• Avoid eagerly invoking lazy ViewManager getters and unnecessary getConstantsForViewManager calls during Bridgeless initialization.
• Add regression coverage for lazy, own, enumerable and one-time getter behavior.
• Platform scope: This targets the Android Bridgeless lazy ViewManager path. iOS does not currently expose this lazy getter path, so no iOS runtime behavior or performance change is expected.

Changelog:

[ANDROID] [FIXED] - Avoid unnecessary getConstantsForViewManager calls during UIManager initialization.

Test Plan:

• yarn flow-check
• yarn test packages/react-native/Libraries/ReactNative --runInBand
• yarn lint --quiet
• yarn format-check
• Verified with Android RNTester offlineDebug that startup no longer triggers eager getConstantsForViewManager calls.

[fairysword]

UIManager lazy ViewManager initialization optimization

Test environment:

• RNTester offlineDebug
• Debug native code with a Hermes bundle loaded from APK assets; Metro/dev support disabled
• Same Android device (V2338A, Android 16)
• logcat cleared and the app force-stopped before each cold start
• The bundle task was forced to rerun before each APK was installed

offlineDebug is a local RNTester configuration created only for these manual performance measurements; it is not an upstream RNTester configuration and is not part of this PR. The proposed patch's automated regression coverage is UIManager-test.js and does not depend on this configuration or on the instrumentation below.

Metric definitions:

• Bundle Load = timestamp(RUN_JS_BUNDLE_END) - timestamp(RUN_JS_BUNDLE_START)
• CONTENT_APPEARED = timestamp(CONTENT_APPEARED) - timestamp(RUN_JS_BUNDLE_START)

1. Temporary ReactInstance instrumentation

The following debug-only instrumentation was added locally to ReactInstance.kt. It is not part of the proposed patch.

import android.util.Log

private fun createConstants(
    viewManagers: List<ViewManager<in Nothing, in Nothing>>,
    customDirectEvents: MutableMap<String, Any>?,
): MutableMap<String, Any> {
  val startNanos = System.nanoTime()
  // Existing implementation...
  try {
    return UIManagerModuleConstantsHelper.createConstants(
        viewManagers,
        null,
        customDirectEvents,
    )
  } finally {
    // Existing marker cleanup...
    if (BuildConfig.DEBUG) {
      Log.d(
          "RNUIManagerPerf",
          "getConstants(eagerViewManagers=${viewManagers.size}) took ${(System.nanoTime() - startNanos) / 1_000_000.0}ms",
      )
    }
  }
}

private fun getConstantsForViewManager(
    viewManager: ViewManager<*, *>,
    customDirectEvents: MutableMap<String, Any>,
): NativeMap {
  val startNanos = System.nanoTime()
  // Existing implementation...
  try {
    val viewManagerConstants =
        UIManagerModuleConstantsHelper.createConstantsForViewManager(
            viewManager,
            null,
            null,
            null,
            customDirectEvents,
        )
    return Arguments.makeNativeMap(viewManagerConstants)
  } finally {
    // Existing trace cleanup...
    if (BuildConfig.DEBUG) {
      Log.d(
          "RNUIManagerPerf",
          "getConstantsForViewManager(${viewManager.name}) took ${(System.nanoTime() - startNanos) / 1_000_000.0}ms",
      )
    }
  }
}

2. Before/after logs

Before: object spread

With ...UIManagerImpl, importing UIManager reads every enumerable lazy ViewManager property. This synchronously calls getConstantsForViewManager for all 20 registered lazy ViewManagers during startup.

D/RNUIManagerPerf: getConstants(eagerViewManagers=0) took 0.937031ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTSafeAreaView) took 15.836355ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTModalHostView) took 6.342136ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidProgressBar) took 4.09651ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidHorizontalScrollView) took 6.418177ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTImageView) took 5.935573ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTText) took 5.849114ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidHorizontalScrollContentView) took 7.902032ms
D/RNUIManagerPerf: getConstantsForViewManager(RNTMyLegacyNativeView) took 3.298698ms
D/RNUIManagerPerf: getConstantsForViewManager(RNTReportFullyDrawnView) took 3.527865ms
D/RNUIManagerPerf: getConstantsForViewManager(UnimplementedNativeView) took 3.425677ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTScrollView) took 6.097032ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTView) took 7.669635ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidDrawerLayout) took 3.646875ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidSwitch) took 3.287812ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidSwipeRefreshLayout) took 3.423437ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidPopupMenu) took 2.970105ms
D/RNUIManagerPerf: getConstantsForViewManager(RNTMyNativeView) took 2.043542ms
D/RNUIManagerPerf: getConstantsForViewManager(AndroidTextInput) took 6.461354ms
D/RNUIManagerPerf: getConstantsForViewManager(RCTSelectableText) took 3.281875ms
D/RNUIManagerPerf: getConstantsForViewManager(VirtualView) took 2.945833ms

The 20 getConstantsForViewManager calls took 104.46 ms cumulatively.

Startup timing from the same run:

Bundle Load: 161ms
CONTENT_APPEARED: 356ms

After: property descriptor composition

After preserving the lazy property descriptors instead of reading their values, startup no longer calls getConstantsForViewManager:

D/RNUIManagerPerf: getConstants(eagerViewManagers=0) took 3.361563ms

Result:

• getConstantsForViewManager startup calls: 20 → 0
• Cumulative synchronous ViewManager configuration work: 104.46 ms → 0 ms

Startup timing from the same run:

Bundle Load: 49ms
CONTENT_APPEARED: 289ms

The marker timings above are one cold-start sample and are included as supporting evidence. The deterministic regression signal is the removal of all 20 synchronous getConstantsForViewManager calls during UIManager module initialization.

[fairysword]

Hi maintainers — gentle ping on this PR, now open for just over two weeks. It preserves lazy ViewManager initialization in Bridgeless UIManager and includes a regression test verifying that getters are not eagerly invoked at module load. Happy to address any feedback or add coverage if helpful. Thanks!

[fairysword]

Hi @rubennorte — gentle follow-up on the review request from last week. This PR is still current and ready for review, with a regression test covering the eager ViewManager getter behavior. I’m happy to address any feedback or adjust the approach. Thanks for your time!