Lazily instantiate native modules

Summary: Instead of sending a list of modules over to JS on startup (and actually blocking script execution) instead provide a proxy object that constructs each of these lazily.

Reviewed By: lexs

Differential Revision: D3936979

fbshipit-source-id: 71bde822f01eb17a29f56c5e60e95e98e207d74d

ReactCommon/cxxreact/JSCNativeModules.cpp

@@ -0,0 +1,63 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+#include "JSCNativeModules.h"
+
+#include <string>
+
+namespace facebook {
+namespace react {
+
+JSCNativeModules::JSCNativeModules(std::shared_ptr<ModuleRegistry> moduleRegistry) :
+  m_moduleRegistry(std::move(moduleRegistry)) {}
+
+JSValueRef JSCNativeModules::getModule(JSContextRef context, JSStringRef jsName) {
+  std::string moduleName = String::ref(jsName).str();
+
+  const auto it = m_objects.find(moduleName);
+  if (it != m_objects.end()) {
+    return static_cast<JSObjectRef>(it->second);
+  }
+
+  auto module = createModule(moduleName, context);
+  if (!module.hasValue()) {
+    return JSValueMakeUndefined(context);
+  }
+
+  // Protect since we'll be holding on to this value, even though JS may not
+  module->makeProtected();
+
+  auto result = m_objects.emplace(std::move(moduleName), std::move(*module)).first;
+  return static_cast<JSObjectRef>(result->second);
+}
+
+void JSCNativeModules::reset() {
+  m_genNativeModuleJS = nullptr;
+  m_objects.clear();
+}
+
+folly::Optional<Object> JSCNativeModules::createModule(const std::string& name, JSContextRef context) {
+  if (!m_genNativeModuleJS) {
+    auto global = Object::getGlobalObject(context);
+    m_genNativeModuleJS = global.getProperty("__fbGenNativeModule").asObject();
+    m_genNativeModuleJS->makeProtected();
+
+    // Initialize the module name list, otherwise getModuleConfig won't work
+    // TODO (pieterdb): fix this in ModuleRegistry
+    m_moduleRegistry->moduleNames();
+  }
+
+  auto result = m_moduleRegistry->getConfig(name);
+  if (!result.hasValue()) {
+    return nullptr;
+  }
+
+  Value moduleInfo = m_genNativeModuleJS->callAsFunction({
+    Value::fromDynamic(context, result->config),
+    JSValueMakeNumber(context, result->index)
+  });
+  CHECK(!moduleInfo.isNull()) << "Module returned from genNativeModule is null";
+
+  return moduleInfo.asObject().getProperty("module").asObject();
+}
+
+} }