[iOS] Data race in `ReactCxxBridge.loading`

[hakonk]

Description

RCTCxxBridge.Loading is not thread safe. This is problematic as it is accessed on the JS thread, and while this example only shows it's accessed as well on the main thread in a test, it is also accessed e.g. here (RCTRootView.m:314-327).

- (void)setAppProperties:(NSDictionary *)appProperties
{
  RCTAssertMainQueue();

  if ([_appProperties isEqualToDictionary:appProperties]) {
    return;
  }

  _appProperties = [appProperties copy];

  if (_contentView && _bridge.valid && !_bridge.loading) {
    [self runApplication:_bridge];
  }
}

Thus, two threads can simultaneously access it in production.

Steps to reproduce

1. Do setup routine as described in README.
2. Open RNTesterPods.xcworkspace
3. Enable TSan for both RNTester and RNTesterUnitTests
4. Run RCTComponentPropsTests with Runtime issue breakpoint enabled.

React Native Version

0.74.3

Affected Platforms

Runtime - iOS

Output of npx react-native info

System:
  OS: macOS 14.5
  CPU: (12) arm64 Apple M2 Pro
  Memory: 2.87 GB / 32.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 20.14.0
    path: ~/.nvm/versions/node/v20.14.0/bin/node
  Yarn:
    version: 1.22.21
    path: ~/.nvm/versions/node/v20.14.0/bin/yarn
  npm:
    version: 10.7.0
    path: ~/.nvm/versions/node/v20.14.0/bin/npm
  Watchman:
    version: 2024.06.10.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.14.2
    path: /Users/user/.rvm/gems/ruby-2.7.2/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 23.5
      - iOS 17.5
      - macOS 14.5
      - tvOS 17.5
      - visionOS 1.2
      - watchOS 10.5
  Android SDK:
    API Levels:
      - "26"
      - "33"
      - "34"
    Build Tools:
      - 26.0.3
      - 30.0.3
      - 33.0.1
      - 34.0.0
      - 35.0.0
    System Images:
      - android-26 | Google APIs Intel x86_64 Atom
      - android-34 | Google APIs ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2023.3 AI-233.14808.21.2331.11709847
  Xcode:
    version: 15.4/15F31d
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.11
    path: /usr/bin/javac
  Ruby:
    version: 2.7.2
    path: /Users/user/.rvm/rubies/ruby-2.7.2/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native: Not Found
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: false
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

WARNING: ThreadSanitizer: data race (pid=41522)
  Write of size 1 at 0x0001077170d8 by thread T5:
    #0 -[RCTCxxBridge _flushPendingCalls] <null> (RNTesterUnitTests:arm64+0x4241e0)
    #1 __53-[RCTCxxBridge executeSourceCode:withSourceURL:sync:]_block_invoke <null> (RNTesterUnitTests:arm64+0x41edac)
    #2 decltype(std::declval<void () block_pointer __strong&>()()) std::__1::__invoke[abi:ue170006]<void () block_pointer __strong&>(&&, decltype(std::declval<void () block_pointer __strong&>()())&&...) <null> (RNTesterUnitTests:arm64+0x44eff4)
    #3 std::__1::__function::__func<void () block_pointer __strong, std::__1::allocator<std::__1::allocator>, void ()>::operator()() <null> (RNTesterUnitTests:arm64+0x44e9c8)
    #4 std::__1::__function::__value_func<void ()>::operator()[abi:ue170006]() const <null> (RNTesterUnitTests:arm64+0x3c6dec)
    #5 std::__1::function<void ()>::operator()() const <null> (RNTesterUnitTests:arm64+0x3c6ad8)
    #6 facebook::react::tryAndReturnError(std::__1::function<void ()> const&) <null> (RNTesterUnitTests:arm64+0x4a7ee8)
    #7 facebook::react::RCTMessageThread::tryFunc(std::__1::function<void ()> const&) <null> (RNTesterUnitTests:arm64+0x50e6b8)
    #8 facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1::operator()() const <null> (RNTesterUnitTests:arm64+0x522b4c)
    #9 decltype(std::declval<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1&>()()) std::__1::__invoke[abi:ue170006]<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1&>(facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1&) <null> (RNTesterUnitTests:arm64+0x5228b0)
    #10 void std::__1::__invoke_void_return_wrapper<void, true>::__call[abi:ue170006]<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1&>(facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1&) <null> (RNTesterUnitTests:arm64+0x5226d4)
    #11 std::__1::__function::__alloc_func<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1, std::__1::allocator<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1>, void ()>::operator()[abi:ue170006]() <null> (RNTesterUnitTests:arm64+0x522638)
    #12 std::__1::__function::__func<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1, std::__1::allocator<facebook::react::RCTMessageThread::runOnQueue(std::__1::function<void ()>&&)::$_1>, void ()>::operator()() <null> (RNTesterUnitTests:arm64+0x51d274)
    #13 std::__1::__function::__value_func<void ()>::operator()[abi:ue170006]() const <null> (RNTesterUnitTests:arm64+0x3c6dec)
    #14 std::__1::function<void ()>::operator()() const <null> (RNTesterUnitTests:arm64+0x3c6ad8)
    #15 invocation function for block in facebook::react::RCTMessageThread::runAsync(std::__1::function<void ()>) <null> (RNTesterUnitTests:arm64+0x50e0e0)
    #16 __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ <null> (CoreFoundation:arm64+0x8dc0c)
    #17 __NSThread__start__ <null> (Foundation:arm64+0x645c60)

  Previous read of size 1 at 0x0001077170d8 by main thread:
    #0 -[RCTCxxBridge isLoading] <null> (RNTesterUnitTests:arm64+0x42b0c8)
    #1 -[RCTBridge isLoading] <null> (RNTesterUnitTests:arm64+0x3b97e4)
    #2 -[RCTComponentPropsTests setUp] <null> (RNTesterUnitTests:arm64+0xe6194)
    #3 __70-[XCTestCase _shouldContinueAfterPerformingSetUpSequenceWithSelector:]_block_invoke.134 <null> (XCTestCore:arm64+0x540d8)

  Location is heap block of size 384 at 0x000107716f80 allocated by main thread:
    #0 calloc <null> (libclang_rt.tsan_iossim_dynamic.dylib:arm64+0x4fc30)
    #1 _malloc_type_calloc_outlined <null> (libsystem_malloc.dylib:arm64+0xf488)
    #2 -[RCTBridge initWithDelegate:bundleURL:moduleProvider:launchOptions:] <null> (RNTesterUnitTests:arm64+0x3b5bb4)
    #3 -[RCTBridge initWithBundleURL:moduleProvider:launchOptions:] <null> (RNTesterUnitTests:arm64+0x3b5798)
    #4 -[RCTComponentPropsTests setUp] <null> (RNTesterUnitTests:arm64+0xe5d9c)
    #5 __70-[XCTestCase _shouldContinueAfterPerformingSetUpSequenceWithSelector:]_block_invoke.134 <null> (XCTestCore:arm64+0x540d8)

  Thread T5 (tid=9796413, running) created by main thread at:
    #0 pthread_create <null> (libclang_rt.tsan_iossim_dynamic.dylib:arm64+0x2bee4)
    #1 -[NSThread startAndReturnError:] <null> (Foundation:arm64+0x6458f0)
    #2 -[RCTBridge setUp] <null> (RNTesterUnitTests:arm64+0x3b8dbc)
    #3 -[RCTBridge initWithDelegate:bundleURL:moduleProvider:launchOptions:] <null> (RNTesterUnitTests:arm64+0x3b5bb4)
    #4 -[RCTBridge initWithBundleURL:moduleProvider:launchOptions:] <null> (RNTesterUnitTests:arm64+0x3b5798)
    #5 -[RCTComponentPropsTests setUp] <null> (RNTesterUnitTests:arm64+0xe5d9c)
    #6 __70-[XCTestCase _shouldContinueAfterPerformingSetUpSequenceWithSelector:]_block_invoke.134 <null> (XCTestCore:arm64+0x540d8)

Reproducer

https://github.com/hakonk/react-native/#main

Screenshots and Videos

No response