Cmake infrastructure for creating components (#784)

*cmake macro to create components for libraries with multiple nodes

Signed-off-by: Siddharth Kucheria <kucheria@usc.edu>

rclcpp_components/src/node_main.cpp.in

@@ -0,0 +1,66 @@
+// Copyright 2019 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "class_loader/class_loader.hpp"
+#include "rclcpp/rclcpp.hpp"
+#include "rclcpp_components/node_factory.hpp"
+#include "rclcpp_components/node_factory_template.hpp"
+
+#define NODE_MAIN_LOGGER_NAME "@node@"
+
+int main(int argc, char * argv[])
+{
+  auto args = rclcpp::init_and_remove_ros_arguments(argc, argv);
+  rclcpp::Logger logger = rclcpp::get_logger(NODE_MAIN_LOGGER_NAME);
+  rclcpp::executors::SingleThreadedExecutor exec;
+  rclcpp::NodeOptions options;
+  options.arguments(args);
+  std::vector<class_loader::ClassLoader * > loaders;
+  std::vector<rclcpp_components::NodeInstanceWrapper> node_wrappers;
+
+  std::string library_name = "@library_name@";
+  std::string class_name = "rclcpp_components::NodeFactoryTemplate<@component@>";
+
+  RCLCPP_DEBUG(logger, "Load library %s", library_name.c_str());
+  auto loader = new class_loader::ClassLoader(library_name);
+  auto classes = loader->getAvailableClasses<rclcpp_components::NodeFactory>();
+  for (auto clazz : classes) {
+    std::string name = clazz.c_str();
+    if (!(name.compare(class_name))) {
+      RCLCPP_DEBUG(logger, "Instantiate class %s", clazz.c_str());
+      auto node_factory = loader->createInstance<rclcpp_components::NodeFactory>(clazz);
+      auto wrapper = node_factory->create_node_instance(options);
+      auto node = wrapper.get_node_base_interface();
+      node_wrappers.push_back(wrapper);
+      exec.add_node(node);
+    }
+  }
+  loaders.push_back(loader);
+
+
+  exec.spin();
+
+  for (auto wrapper : node_wrappers) {
+    exec.remove_node(wrapper.get_node_base_interface());
+  }
+  node_wrappers.clear();
+
+  rclcpp::shutdown();
+
+  return 0;
+}