Partially restore feature flag to disable event loop on bridgeless (#48892)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48892

Changelog: [internal]

Reviewed By: javache, Abbondanzo

Differential Revision: D68557746

fbshipit-source-id: d94877d03dc6ea2bf6bca45da77a0a769fa0efeb

packages/react-native/Libraries/Core/setUpTimers.js

@@ -10,6 +10,9 @@
 
 'use strict';
 
+const ReactNativeFeatureFlags = require('../../src/private/featureflags/ReactNativeFeatureFlags');
+const NativeReactNativeFeatureFlags =
+  require('../../src/private/featureflags/specs/NativeReactNativeFeatureFlags').default;
 const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
 
 if (__DEV__) {
@@ -18,46 +21,19 @@ if (__DEV__) {
   }
 }
 
+const isEventLoopEnabled = (() => {
+  if (NativeReactNativeFeatureFlags == null) {
+    return false;
+  }
+
+  return (
+    ReactNativeFeatureFlags.enableBridgelessArchitecture() &&
+    !ReactNativeFeatureFlags.disableEventLoopOnBridgeless()
+  );
+})();
+
 // In bridgeless mode, timers are host functions installed from cpp.
-if (global.RN$Bridgeless === true) {
-  polyfillGlobal(
-    'requestIdleCallback',
-    () =>
-      require('../../src/private/webapis/idlecallbacks/specs/NativeIdleCallbacks')
-        .default.requestIdleCallback,
-  );
-
-  polyfillGlobal(
-    'cancelIdleCallback',
-    () =>
-      require('../../src/private/webapis/idlecallbacks/specs/NativeIdleCallbacks')
-        .default.cancelIdleCallback,
-  );
-
-  // This is the flag that tells React to use `queueMicrotask` to batch state
-  // updates, instead of using the scheduler to schedule a regular task.
-  // We use a global variable because we don't currently have any other
-  // mechanism to pass feature flags from RN to React in OSS.
-  global.RN$enableMicrotasksInReact = true;
-
-  polyfillGlobal(
-    'queueMicrotask',
-    () =>
-      require('../../src/private/webapis/microtasks/specs/NativeMicrotasks')
-        .default.queueMicrotask,
-  );
-
-  // We shim the immediate APIs via `queueMicrotask` to maintain the backward
-  // compatibility.
-  polyfillGlobal(
-    'setImmediate',
-    () => require('./Timers/immediateShim').setImmediate,
-  );
-  polyfillGlobal(
-    'clearImmediate',
-    () => require('./Timers/immediateShim').clearImmediate,
-  );
-} else {
+if (global.RN$Bridgeless !== true) {
   /**
    * Set up timers.
    * You can use this module directly, or just require InitializeCore.
@@ -83,7 +59,50 @@ if (global.RN$Bridgeless === true) {
   defineLazyTimer('cancelAnimationFrame');
   defineLazyTimer('requestIdleCallback');
   defineLazyTimer('cancelIdleCallback');
+} else if (isEventLoopEnabled) {
+  polyfillGlobal(
+    'requestIdleCallback',
+    () =>
+      require('../../src/private/webapis/idlecallbacks/specs/NativeIdleCallbacks')
+        .default.requestIdleCallback,
+  );
 
+  polyfillGlobal(
+    'cancelIdleCallback',
+    () =>
+      require('../../src/private/webapis/idlecallbacks/specs/NativeIdleCallbacks')
+        .default.cancelIdleCallback,
+  );
+}
+
+// We need to check if the native module is available before accessing the
+// feature flag, because otherwise the API would throw an error in the legacy
+// architecture in OSS, where the native module isn't available.
+if (isEventLoopEnabled) {
+  // This is the flag that tells React to use `queueMicrotask` to batch state
+  // updates, instead of using the scheduler to schedule a regular task.
+  // We use a global variable because we don't currently have any other
+  // mechanism to pass feature flags from RN to React in OSS.
+  global.RN$enableMicrotasksInReact = true;
+
+  polyfillGlobal(
+    'queueMicrotask',
+    () =>
+      require('../../src/private/webapis/microtasks/specs/NativeMicrotasks')
+        .default.queueMicrotask,
+  );
+
+  // We shim the immediate APIs via `queueMicrotask` to maintain the backward
+  // compatibility.
+  polyfillGlobal(
+    'setImmediate',
+    () => require('./Timers/immediateShim').setImmediate,
+  );
+  polyfillGlobal(
+    'clearImmediate',
+    () => require('./Timers/immediateShim').clearImmediate,
+  );
+} else {
   // Polyfill it with promise (regardless it's polyfilled or native) otherwise.
   polyfillGlobal(
     'queueMicrotask',
@@ -93,12 +112,14 @@ if (global.RN$Bridgeless === true) {
   // When promise was polyfilled hence is queued to the RN microtask queue,
   // we polyfill the immediate APIs as aliases to the ReactNativeMicrotask APIs.
   // Note that in bridgeless mode, immediate APIs are installed from cpp.
-  polyfillGlobal(
-    'setImmediate',
-    () => require('./Timers/JSTimers').queueReactNativeMicrotask,
-  );
-  polyfillGlobal(
-    'clearImmediate',
-    () => require('./Timers/JSTimers').clearReactNativeMicrotask,
-  );
+  if (global.RN$Bridgeless !== true) {
+    polyfillGlobal(
+      'setImmediate',
+      () => require('./Timers/JSTimers').queueReactNativeMicrotask,
+    );
+    polyfillGlobal(
+      'clearImmediate',
+      () => require('./Timers/JSTimers').clearReactNativeMicrotask,
+    );
+  }
 }

packages/react-native/ReactCommon/react/nativemodule/featureflags/NativeReactNativeFeatureFlags.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<9e4ac7a270dd74f6978374d8e2c05013>>
+ * @generated SignedSource<<70ce0689b8452f99877fa46b9f6b6215>>
  */
 
 /**
@@ -54,6 +54,13 @@ bool NativeReactNativeFeatureFlags::completeReactInstanceCreationOnBgThreadOnAnd
   return ReactNativeFeatureFlags::completeReactInstanceCreationOnBgThreadOnAndroid();
 }
 
+bool NativeReactNativeFeatureFlags::disableEventLoopOnBridgeless(
+    jsi::Runtime& /*runtime*/) {
+  // This flag is configured with `skipNativeAPI: true`.
+  // TODO(T204838867): Implement support for optional methods in C++ TM codegen and remove the method definition altogether.
+  return false;
+}
+
 bool NativeReactNativeFeatureFlags::disableMountItemReorderingAndroid(
     jsi::Runtime& /*runtime*/) {
   return ReactNativeFeatureFlags::disableMountItemReorderingAndroid();

packages/react-native/ReactCommon/react/nativemodule/featureflags/NativeReactNativeFeatureFlags.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<c11c50b272b571325ee3947ec53f0050>>
+ * @generated SignedSource<<3aadd0d890f3dac9fee5bc465d759203>>
  */
 
 /**
@@ -41,6 +41,8 @@ class NativeReactNativeFeatureFlags
 
   bool completeReactInstanceCreationOnBgThreadOnAndroid(jsi::Runtime& runtime);
 
+  bool disableEventLoopOnBridgeless(jsi::Runtime& runtime);
+
   bool disableMountItemReorderingAndroid(jsi::Runtime& runtime);
 
   bool enableAccumulatedUpdatesInRawPropsAndroid(jsi::Runtime& runtime);

packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.config.js

@@ -66,6 +66,16 @@ const definitions: FeatureFlagDefinitions = {
         purpose: 'release',
       },
     },
+    disableEventLoopOnBridgeless: {
+      defaultValue: false,
+      metadata: {
+        description:
+          'The bridgeless architecture enables the event loop by default. This feature flag allows us to force disabling it in specific instances.',
+        expectedReleaseValue: true,
+        purpose: 'release',
+      },
+      skipNativeAPI: true,
+    },
     disableMountItemReorderingAndroid: {
       defaultValue: false,
       metadata: {

packages/react-native/src/private/featureflags/ReactNativeFeatureFlags.js

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<811a054f0ada56d8cc1ed21c6930fc52>>
+ * @generated SignedSource<<43c428552b2f180bccddcfe62fc36697>>
  * @flow strict
  */
 
@@ -49,6 +49,7 @@ export type ReactNativeFeatureFlags = $ReadOnly<{
   commonTestFlag: Getter<boolean>,
   commonTestFlagWithoutNativeImplementation: Getter<boolean>,
   completeReactInstanceCreationOnBgThreadOnAndroid: Getter<boolean>,
+  disableEventLoopOnBridgeless: Getter<boolean>,
   disableMountItemReorderingAndroid: Getter<boolean>,
   enableAccumulatedUpdatesInRawPropsAndroid: Getter<boolean>,
   enableBridgelessArchitecture: Getter<boolean>,
@@ -172,6 +173,10 @@ export const commonTestFlagWithoutNativeImplementation: Getter<boolean> = create
  * Do not wait for a main-thread dispatch to complete init to start executing work on the JS thread on Android
  */
 export const completeReactInstanceCreationOnBgThreadOnAndroid: Getter<boolean> = createNativeFlagGetter('completeReactInstanceCreationOnBgThreadOnAndroid', true);
+/**
+ * The bridgeless architecture enables the event loop by default. This feature flag allows us to force disabling it in specific instances.
+ */
+export const disableEventLoopOnBridgeless: Getter<boolean> = createNativeFlagGetter('disableEventLoopOnBridgeless', false);
 /**
  * Prevent FabricMountingManager from reordering mountitems, which may lead to invalid state on the UI thread
  */

packages/react-native/src/private/featureflags/specs/NativeReactNativeFeatureFlags.js

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<bcb501bc8f71f02c82a58b898e73d9a0>>
+ * @generated SignedSource<<2dbeae49bc79bdbbf06c54273b2e2b9b>>
  * @flow strict
  */
 
@@ -26,6 +26,7 @@ export interface Spec extends TurboModule {
   +commonTestFlag?: () => boolean;
   +commonTestFlagWithoutNativeImplementation?: () => boolean;
   +completeReactInstanceCreationOnBgThreadOnAndroid?: () => boolean;
+  +disableEventLoopOnBridgeless?: () => boolean;
   +disableMountItemReorderingAndroid?: () => boolean;
   +enableAccumulatedUpdatesInRawPropsAndroid?: () => boolean;
   +enableBridgelessArchitecture?: () => boolean;