Make the choice of bridge based on an optional delegate method

Reviewed By: javache

Differential Revision: D4679644

fbshipit-source-id: f53e554e283fdb0b59c41623e690fd1a21e03a57

React/Base/RCTBridge.m

@@ -302,7 +302,31 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
 
 - (void)createBatchedBridge
 {
-  self.batchedBridge = [[RCTBatchedBridge alloc] initWithParentBridge:self];
+  // In order to facilitate switching between bridges with only build
+  // file changes, this uses reflection to check which bridges are
+  // available.  This is a short-term hack until RCTBatchedBridge is
+  // removed.
+
+  Class batchedBridgeClass = objc_lookUpClass("RCTBatchedBridge");
+  Class cxxBridgeClass = objc_lookUpClass("RCTCxxBridge");
+
+  Class implClass = nil;
+
+  if ([self.delegate respondsToSelector:@selector(shouldBridgeUseCxxBridge:)]) {
+    if ([self.delegate shouldBridgeUseCxxBridge:self]) {
+      implClass = cxxBridgeClass;
+    } else {
+      implClass = batchedBridgeClass;
+    }
+  } else if (batchedBridgeClass != nil) {
+    implClass = batchedBridgeClass;
+  } else if (cxxBridgeClass != nil) {
+    implClass = cxxBridgeClass;
+  }
+
+  RCTAssert(implClass != nil, @"No bridge implementation is available, giving up.");
+
+  self.batchedBridge = [[implClass alloc] initWithParentBridge:self];
 }
 
 - (BOOL)isLoading

React/Base/RCTBridgeDelegate.h

@@ -91,6 +91,20 @@
  */
 - (BOOL)shouldBridgeUseCustomJSC:(RCTBridge *)bridge;
 
+/**
+ * Configure whether the legacy RCTBatchedBridge or new RCTCxxBridge
+ * should be used.  If this method is implemented and the specified
+ * bridge is not linked in, startup will fail.  If this method is not
+ * implemented, the implementation will default to RCTBatchedBridge,
+ * but if it is not linked in, will try RCTCxxBridge instead.  If
+ * neither bridge is linked in, startup will fail.  This order will be
+ * reversed in the near future, as the legacy bridge is closer to
+ * being removed.
+ *
+ * @experimental
+ */
+- (BOOL)shouldBridgeUseCxxBridge:(RCTBridge *)bridge;
+
 /**
  * The bridge will automatically attempt to load the JS source code from the
  * location specified by the `sourceURLForBridge:` method, however, if you want

React/CxxBridge/RCTCxxBridge.h

@@ -1,17 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-#import <React/RCTBridge.h>
-
-@interface RCTCxxBridge : RCTBridge
-
-+ (void)enable;
-+ (void)disable;
-
-@end

React/CxxBridge/RCTCxxBridge.mm

@@ -9,8 +9,6 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
-#include "RCTCxxBridge.h"
-
 #include <atomic>
 #include <future>
 #include <libkern/OSAtomic.h>
@@ -48,6 +46,9 @@
 #import <React/RCTFBSystrace.h>
 #endif
 
+@interface RCTCxxBridge : RCTBridge
+@end
+
 #define RCTAssertJSThread() \
   RCTAssert(self.executorClass || self->_jsThread == [NSThread currentThread], \
             @"This method must be called on JS thread")
@@ -92,8 +93,6 @@ static bool isRAMBundle(NSData *script) {
   return parseTypeFromHeader(header) == ScriptTag::RAMBundle;
 }
 
-static std::atomic_bool cxxBridgeEnabled(false);
-
 @interface RCTCxxBridge ()
 
 @property (nonatomic, weak, readonly) RCTBridge *parentBridge;
@@ -121,19 +120,6 @@ struct RCTInstanceCallback : public InstanceCallback {
   void onExecutorStopped(ExecutorToken) override {}
 };
 
-@implementation RCTBridge (CxxBridge)
-
-- (void)CXX_createBatchedBridge
-{
-  if (cxxBridgeEnabled) {
-    self.batchedBridge = [[RCTCxxBridge alloc] initWithParentBridge:self];
-  } else {
-    self.batchedBridge = [[RCTBatchedBridge alloc] initWithParentBridge:self];
-  }
-}
-
-@end
-
 @implementation RCTCxxBridge
 {
   BOOL _wasBatchActive;
@@ -172,35 +158,6 @@ struct RCTInstanceCallback : public InstanceCallback {
   }
 }
 
-+ (void)swizzleBridge
-{
-  // Swizzle RCTBridge to use this, instead of RCTBatchedBridge
-  static dispatch_once_t once;
-  dispatch_once(&once, ^{
-    RCTSwapInstanceMethods([RCTBridge class],
-                           NSSelectorFromString(@"createBatchedBridge"),
-                           @selector(CXX_createBatchedBridge));
-  });
-}
-
-+ (void)enable
-{
-  [RCTCxxBridge swizzleBridge];
-#ifdef WITH_FBSYSTRACE
-  [RCTFBSystrace registerCallbacks];
-#endif
-  cxxBridgeEnabled = true;
-}
-
-+ (void)disable
-{
-  [RCTCxxBridge swizzleBridge];
-#ifdef WITH_FBSYSTRACE
-  [RCTFBSystrace unregisterCallbacks];
-#endif
-  cxxBridgeEnabled = false;
-}
-
 - (JSContext *)jsContext
 {
   return contextForGlobalContextRef((JSGlobalContextRef) self->_reactInstance->getJavaScriptContext());