Verify exported modules only once to support dynamic context in DEBUG…

…-mode

Summary:
**Motivation:** We have a project that dynamically changes classes in runtime. This component is initialised within the React Native context. Therefor `RCTBatchedBridge` copies the classes before changes are made to them. While React Native is running, changes are made to the classes dynamically. When the project reloads the `RCTBatchedBridge`, it now has an invalid list of classes containing trash pointers. This causes the project to crash on https://github.com/facebook/react-native/blob/master/React/Base/RCTBatchedBridge.m#L288 with EXC_BAD_ACCESS in the DEBUG-mode.

**Solution:** Copy the class list on each reload to get the current state. Since this is only a DEBUG-feature the overhead of this should not be a major issue.
Closes #9541

Differential Revision: D3775012

Pulled By: javache

fbshipit-source-id: d55fa0742ca100d8018c73080230cf718aa5a7e9

React/Base/RCTBatchedBridge.m

@@ -266,38 +266,38 @@ - (void)initModulesWithDispatchGroup:(dispatch_group_t)dispatchGroup
     extraModules = self.moduleProvider();
   }
 
-  if (RCT_DEBUG && !RCTRunningInTestEnvironment()) {
-    // Check for unexported modules
-    static Class *classes;
-    static unsigned int classCount;
-    static dispatch_once_t onceToken;
-    dispatch_once(&onceToken, ^{
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    if (RCT_DEBUG && !RCTRunningInTestEnvironment()) {
+      // Check for unexported modules
+      Class *classes;
+      unsigned int classCount;
       classes = objc_copyClassList(&classCount);
-    });
 
-    NSMutableSet *moduleClasses = [NSMutableSet new];
-    [moduleClasses addObjectsFromArray:RCTGetModuleClasses()];
-    [moduleClasses addObjectsFromArray:[extraModules valueForKeyPath:@"class"]];
+      NSMutableSet *moduleClasses = [NSMutableSet new];
+      [moduleClasses addObjectsFromArray:RCTGetModuleClasses()];
+      [moduleClasses addObjectsFromArray:[extraModules valueForKeyPath:@"class"]];
 
-    for (unsigned int i = 0; i < classCount; i++)
-    {
-      Class cls = classes[i];
-      Class superclass = cls;
-      while (superclass)
+      for (unsigned int i = 0; i < classCount; i++)
       {
-        if (class_conformsToProtocol(superclass, @protocol(RCTBridgeModule)))
+        Class cls = classes[i];
+        Class superclass = cls;
+        while (superclass)
         {
-          if (![moduleClasses containsObject:cls] &&
-              ![cls respondsToSelector:@selector(moduleName)]) {
-            RCTLogWarn(@"Class %@ was not exported. Did you forget to use "
-                       "RCT_EXPORT_MODULE()?", cls);
+          if (class_conformsToProtocol(superclass, @protocol(RCTBridgeModule)))
+          {
+            if (![moduleClasses containsObject:cls] &&
+                ![cls respondsToSelector:@selector(moduleName)]) {
+              RCTLogWarn(@"Class %@ was not exported. Did you forget to use "
+                         "RCT_EXPORT_MODULE()?", cls);
+            }
+            break;
           }
-          break;
+          superclass = class_getSuperclass(superclass);
         }
-        superclass = class_getSuperclass(superclass);
       }
     }
-  }
+  });
 
   NSMutableArray<Class> *moduleClassesByID = [NSMutableArray new];
   NSMutableArray<RCTModuleData *> *moduleDataByID = [NSMutableArray new];