From 06c88be6e370a17cba0e4b4f679fc32b86963c30 Mon Sep 17 00:00:00 2001
From: Ramanpreet Nara <ramanpreet@meta.com>
Date: Wed, 19 Mar 2025 21:16:05 -0700
Subject: [PATCH] Make PlatformConstants use main queue setup (#50111)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50111

## Rationale
Rendering can now include main -> js sync calls.

If we allow js -> main sync calls during rendering, react native can deadlock.

So, this diff moves the js -> main sync calls to "main queue module setup", which occurs before rendering.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D71480047

fbshipit-source-id: e36a4dd317bbbf46a6766f01fbf4d69a83a45c17
---
 .../React/CoreModules/RCTPlatform.mm          | 57 ++++++++++---------
 packages/react-native/package.json            |  8 ++-
 2 files changed, 37 insertions(+), 28 deletions(-)

diff --git a/packages/react-native/React/CoreModules/RCTPlatform.mm b/packages/react-native/React/CoreModules/RCTPlatform.mm
index ec8a5f3220e..2aa4e28be8e 100644
--- a/packages/react-native/React/CoreModules/RCTPlatform.mm
+++ b/packages/react-native/React/CoreModules/RCTPlatform.mm
@@ -10,6 +10,7 @@
 #import <UIKit/UIKit.h>
 
 #import <FBReactNativeSpec/FBReactNativeSpec.h>
+#import <React/RCTInitializing.h>
 #import <React/RCTUtils.h>
 #import <React/RCTVersion.h>
 
@@ -39,10 +40,12 @@ static NSString *interfaceIdiom(UIUserInterfaceIdiom idiom)
   }
 }
 
-@interface RCTPlatform () <NativePlatformConstantsIOSSpec>
+@interface RCTPlatform () <NativePlatformConstantsIOSSpec, RCTInitializing>
 @end
 
-@implementation RCTPlatform
+@implementation RCTPlatform {
+  ModuleConstants<JS::NativePlatformConstantsIOS::Constants> _constants;
+}
 
 RCT_EXPORT_MODULE(PlatformConstants)
 
@@ -51,6 +54,29 @@ RCT_EXPORT_MODULE(PlatformConstants)
   return YES;
 }
 
+- (void)initialize
+{
+  UIDevice *device = [UIDevice currentDevice];
+  auto versions = RCTGetReactNativeVersion();
+  _constants = typedConstants<JS::NativePlatformConstantsIOS::Constants>({
+      .forceTouchAvailable = RCTForceTouchAvailable() ? true : false,
+      .osVersion = [device systemVersion],
+      .systemName = [device systemName],
+      .interfaceIdiom = interfaceIdiom([device userInterfaceIdiom]),
+      .isTesting = RCTRunningInTestEnvironment() ? true : false,
+      .reactNativeVersion = JS::NativePlatformConstantsIOS::ConstantsReactNativeVersion::Builder(
+          {.minor = [versions[@"minor"] doubleValue],
+           .major = [versions[@"major"] doubleValue],
+           .patch = [versions[@"patch"] doubleValue],
+           .prerelease = [versions[@"prerelease"] isKindOfClass:[NSNull class]] ? nullptr : versions[@"prerelease"]}),
+#if TARGET_OS_MACCATALYST
+      .isMacCatalyst = true,
+#else
+      .isMacCatalyst = false,
+#endif
+  });
+}
+
 - (dispatch_queue_t)methodQueue
 {
   return dispatch_get_main_queue();
@@ -59,35 +85,12 @@ RCT_EXPORT_MODULE(PlatformConstants)
 // TODO: Use the generated struct return type.
 - (ModuleConstants<JS::NativePlatformConstantsIOS::Constants>)constantsToExport
 {
-  return (ModuleConstants<JS::NativePlatformConstantsIOS::Constants>)[self getConstants];
+  return _constants;
 }
 
 - (ModuleConstants<JS::NativePlatformConstantsIOS::Constants>)getConstants
 {
-  __block ModuleConstants<JS::NativePlatformConstantsIOS::Constants> constants;
-  RCTUnsafeExecuteOnMainQueueSync(^{
-    UIDevice *device = [UIDevice currentDevice];
-    auto versions = RCTGetReactNativeVersion();
-    constants = typedConstants<JS::NativePlatformConstantsIOS::Constants>({
-        .forceTouchAvailable = RCTForceTouchAvailable() ? true : false,
-        .osVersion = [device systemVersion],
-        .systemName = [device systemName],
-        .interfaceIdiom = interfaceIdiom([device userInterfaceIdiom]),
-        .isTesting = RCTRunningInTestEnvironment() ? true : false,
-        .reactNativeVersion = JS::NativePlatformConstantsIOS::ConstantsReactNativeVersion::Builder(
-            {.minor = [versions[@"minor"] doubleValue],
-             .major = [versions[@"major"] doubleValue],
-             .patch = [versions[@"patch"] doubleValue],
-             .prerelease = [versions[@"prerelease"] isKindOfClass:[NSNull class]] ? nullptr : versions[@"prerelease"]}),
-#if TARGET_OS_MACCATALYST
-        .isMacCatalyst = true,
-#else
-        .isMacCatalyst = false,
-#endif
-    });
-  });
-
-  return constants;
+  return _constants;
 }
 
 - (std::shared_ptr<TurboModule>)getTurboModule:(const ObjCTurboModule::InitParams &)params
diff --git a/packages/react-native/package.json b/packages/react-native/package.json
index 6fdcfa48049..63ca1cb983d 100644
--- a/packages/react-native/package.json
+++ b/packages/react-native/package.json
@@ -149,7 +149,13 @@
       {
         "name": "FBReactNativeSpec",
         "type": "modules",
-        "ios": {},
+        "ios": {
+          "modules": {
+            "PlatformConstants": {
+              "unstableRequiresMainQueueSetup": true
+            }
+          }
+        },
         "android": {},
         "jsSrcsDir": "src"
       },