From 855d411321119e79f899c7420a5a435506fb6cbf Mon Sep 17 00:00:00 2001
From: Nick Lockwood <nicklockwood@fb.com>
Date: Tue, 9 Feb 2016 03:29:18 -0800
Subject: [PATCH] Moved constants export to bridge init

Summary:
public
Lazy export of module constants required a sync dispatch to the main thread, which was deadlocking in some of our projects.

This moves the constants export to the initial bridge init, which may slightly increase initial startup time, but avoids the deadlock.

Reviewed By: javache

Differential Revision: D2911295

fb-gh-sync-id: 0d14a629ac4fc7ee21acd293c09595c18232659b
shipit-source-id: 0d14a629ac4fc7ee21acd293c09595c18232659b
---
 React/Base/RCTBatchedBridge.m |  7 ++++---
 React/Base/RCTModuleData.m    | 15 ++++++++-------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/React/Base/RCTBatchedBridge.m b/React/Base/RCTBatchedBridge.m
index 6ca0fad9c..debc00d9a 100644
--- a/React/Base/RCTBatchedBridge.m
+++ b/React/Base/RCTBatchedBridge.m
@@ -282,10 +282,11 @@ RCT_EXTERN NSArray<Class> *RCTGetModuleClasses(void);
     id module = preregisteredModules[moduleName];
     if (!module) {
       // Check if the module class, or any of its superclasses override init
-      // or setBridge:. If they do, we assume that they are expecting to be
-      // initialized when the bridge first loads.
+      // or setBridge:, or has exported constants. If they do, we assume that
+      // they are expecting to be initialized when the bridge first loads.
       if ([moduleClass instanceMethodForSelector:@selector(init)] != objectInitMethod ||
-          [moduleClass instancesRespondToSelector:setBridgeSelector]) {
+          [moduleClass instancesRespondToSelector:setBridgeSelector] ||
+          RCTClassOverridesInstanceMethod(moduleClass, @selector(constantsToExport))) {
         module = [moduleClass new];
         if (!module) {
           module = (id)kCFNull;
diff --git a/React/Base/RCTModuleData.m b/React/Base/RCTModuleData.m
index 9d4b57539..78ef8471e 100644
--- a/React/Base/RCTModuleData.m
+++ b/React/Base/RCTModuleData.m
@@ -17,6 +17,7 @@
 
 @implementation RCTModuleData
 {
+  NSDictionary<NSString *, id> *_constantsToExport;
   NSString *_queueName;
   __weak RCTBridge *_bridge;
   NSLock *_instanceLock;
@@ -79,6 +80,11 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
     [[NSNotificationCenter defaultCenter] postNotificationName:RCTDidInitializeModuleNotification
                                                         object:_bridge
                                                       userInfo:@{@"module": _instance}];
+
+    if (RCTClassOverridesInstanceMethod(_moduleClass, @selector(constantsToExport))) {
+      RCTAssertMainThread();
+      _constantsToExport = [_instance constantsToExport];
+    }
   }
 }
 
@@ -181,13 +187,8 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
 
 - (NSArray *)config
 {
-  __block NSDictionary<NSString *, id> *constants;
-  if (RCTClassOverridesInstanceMethod(_moduleClass, @selector(constantsToExport))) {
-    [self instance];
-    RCTExecuteOnMainThread(^{
-      constants = [_instance constantsToExport];
-    }, YES);
-  }
+  __block NSDictionary<NSString *, id> *constants = _constantsToExport;
+  _constantsToExport = nil; // Not needed any more
 
   if (constants.count == 0 && self.methods.count == 0) {
     return (id)kCFNull; // Nothing to export