Defer constants gathering until after setup

Reviewed By: javache

Differential Revision: D2986095

fb-gh-sync-id: 1f449e69ca74466e7951d621ceaf624abe034139
shipit-source-id: 1f449e69ca74466e7951d621ceaf624abe034139

React/Base/RCTBatchedBridge.m

@@ -342,6 +342,12 @@ RCT_EXTERN NSArray<Class> *RCTGetModuleClasses(void);
     }
   }
 
+  for (RCTModuleData *moduleData in _moduleDataByID) {
+    if (moduleData.hasInstance) {
+      [moduleData gatherConstants];
+    }
+  }
+
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
 

React/Base/RCTModuleData.h

@@ -37,6 +37,14 @@
  */
 - (void)finishSetupForInstance;
 
+/**
+ * Calls `constantsToExport` on the module and stores the result. Note that
+ * this will init the module if it has not already been created. This method
+ * can be called on any thread, but may block the main thread briefly if the
+ * module implements `constantsToExport`.
+ */
+- (void)gatherConstants;
+
 @property (nonatomic, strong, readonly) Class moduleClass;
 @property (nonatomic, copy, readonly) NSString *name;
 

React/Base/RCTModuleData.m

@@ -80,11 +80,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
     [[NSNotificationCenter defaultCenter] postNotificationName:RCTDidInitializeModuleNotification
                                                         object:_bridge
                                                       userInfo:@{@"module": _instance}];
-
-    if (RCTClassOverridesInstanceMethod(_moduleClass, @selector(constantsToExport))) {
-      RCTAssertMainThread();
-      _constantsToExport = [_instance constantsToExport];
-    }
   }
 }
 
@@ -140,7 +135,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
   [_instanceLock unlock];
 
   [self finishSetupForInstance];
-
   return _instance;
 }
 
@@ -185,10 +179,23 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
   return _methods;
 }
 
+- (void)gatherConstants
+{
+  if (!_constantsToExport) {
+    if (RCTClassOverridesInstanceMethod(_moduleClass, @selector(constantsToExport))) {
+      RCTAssert(_instance, @"constantsToExport called before instance created.");
+      RCTExecuteOnMainThread(^{
+        _constantsToExport = [_instance constantsToExport] ?: @{};
+      }, YES);
+    } else {
+      _constantsToExport = @{};
+    }
+  }
+}
+
 - (NSArray *)config
 {
   __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