From e549f6984e2125969fd11a5b8f4e2df866ac0495 Mon Sep 17 00:00:00 2001
From: Ramanpreet Nara <ramanpreet@fb.com>
Date: Thu, 9 Jul 2020 16:22:44 -0700
Subject: [PATCH] Gate TurboModule eager initialization

Summary:
TurboModule eager initialization is a bit dangerous if we get it wrong, which we did (twice): T69449176.

This diff gates TurboModule eager init behind a MC, so that we can control (i.e: turn off/on, and do gradually rollout of) TurobModule eager initialization in isolation from the larger TurboModules experiment.

Changelog: [Internal]

Reviewed By: PeteTheHeat

Differential Revision: D22460359

fbshipit-source-id: 3b8dce0529f1739bd68b8b16d6a28aa572d82c2c
---
 React/Base/RCTBridge.h                                |  4 ++++
 React/Base/RCTBridge.m                                | 11 +++++++++++
 React/CxxBridge/RCTCxxBridge.mm                       |  2 +-
 .../core/platform/ios/RCTTurboModuleManager.mm        |  7 ++++++-
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/React/Base/RCTBridge.h b/React/Base/RCTBridge.h
index 55025c416f1..a7fb8d8c763 100644
--- a/React/Base/RCTBridge.h
+++ b/React/Base/RCTBridge.h
@@ -158,6 +158,10 @@ RCT_EXTERN NSString *RCTBridgeModuleNameForClass(Class bridgeModuleClass);
 RCT_EXTERN BOOL RCTTurboModuleEnabled(void);
 RCT_EXTERN void RCTEnableTurboModule(BOOL enabled);
 
+// Turn on TurboModule eager initialization
+RCT_EXTERN BOOL RCTTurboModuleEagerInitEnabled(void);
+RCT_EXTERN void RCTEnableTurboModuleEagerInit(BOOL enabled);
+
 /**
  * Async batched bridge used to communicate with the JavaScript application.
  */
diff --git a/React/Base/RCTBridge.m b/React/Base/RCTBridge.m
index b14c62f7baa..91f6b1b1406 100644
--- a/React/Base/RCTBridge.m
+++ b/React/Base/RCTBridge.m
@@ -115,6 +115,17 @@ void RCTEnableTurboModule(BOOL enabled)
   turboModuleEnabled = enabled;
 }
 
+static BOOL turboModuleEagerInitEnabled = NO;
+BOOL RCTTurboModuleEagerInitEnabled(void)
+{
+  return turboModuleEagerInitEnabled;
+}
+
+void RCTEnableTurboModuleEagerInit(BOOL enabled)
+{
+  turboModuleEagerInitEnabled = enabled;
+}
+
 @interface RCTBridge () <RCTReloadListener>
 @end
 
diff --git a/React/CxxBridge/RCTCxxBridge.mm b/React/CxxBridge/RCTCxxBridge.mm
index f3ad20c6ac3..ed0ace43547 100644
--- a/React/CxxBridge/RCTCxxBridge.mm
+++ b/React/CxxBridge/RCTCxxBridge.mm
@@ -385,7 +385,7 @@ struct RCTInstanceCallback : public InstanceCallback {
    * id<RCTCxxBridgeDelegate> jsExecutorFactory may create and assign an id<RCTTurboModuleRegistry> object to
    * RCTCxxBridge If id<RCTTurboModuleRegistry> is assigned by this time, eagerly initialize all TurboModules
    */
-  if (_turboModuleRegistry) {
+  if (_turboModuleRegistry && RCTTurboModuleEagerInitEnabled()) {
     for (NSString *moduleName in [_turboModuleRegistry eagerInitModuleNames]) {
       [_turboModuleRegistry moduleForName:[moduleName UTF8String]];
     }
diff --git a/ReactCommon/turbomodule/core/platform/ios/RCTTurboModuleManager.mm b/ReactCommon/turbomodule/core/platform/ios/RCTTurboModuleManager.mm
index e0db1ecea87..0656a085a16 100644
--- a/ReactCommon/turbomodule/core/platform/ios/RCTTurboModuleManager.mm
+++ b/ReactCommon/turbomodule/core/platform/ios/RCTTurboModuleManager.mm
@@ -396,7 +396,12 @@ static Class getFallbackClassFromName(const char *name)
       };
 
       if ([self _requiresMainQueueSetup:moduleClass]) {
-        if (!RCTIsMainQueue()) {
+        /**
+         * When TurboModule eager initialization is disabled, we expect TurboModules requiring main queue setup to be
+         * required on background threads.
+         * TODO(T69449176) Roll out TurboModule eager initialization, and remove this check.
+         */
+        if (!RCTIsMainQueue() && !RCTTurboModuleEagerInitEnabled()) {
           RCTLogWarn(
               @"TurboModule \"%@\" requires synchronous dispatch onto the main queue to be initialized. This may lead to deadlock.",
               moduleClass);