[Proposal] Adding single message getting API to rclcpp

  ros2/rclcpp#1953

Signed-off-by: Tomoya Fujita <[email protected]>

prover_rclcpp/CMakeLists.txt

@@ -89,6 +89,7 @@ custom_executable(rclcpp_1827)
 custom_executable(rclcpp_1876)
 custom_executable(rclcpp_1915)
 custom_executable(rclcpp_1925)
+custom_executable(rclcpp_1953)
 custom_executable(rclpy_881)
 
 custom_executable(rmw_fastrtps_554)

prover_rclcpp/src/rclcpp_1953.cpp

@@ -0,0 +1,69 @@
+#include <iostream>
+#include <thread>
+#include <string>
+
+#include <rclcpp/node.hpp>
+#include <rclcpp/rclcpp.hpp>
+#include <rclcpp/wait_for_message.hpp>
+#include <std_msgs/msg/string.hpp>
+
+using namespace std::chrono_literals;
+
+
+/// Get current node state in a loop
+void wait_for_messages(std::shared_ptr<rclcpp::Node> node) {
+	// infinite loop to receive the messages
+   	while (rclcpp::ok()) {
+		std_msgs::msg::String out;
+		auto ret = rclcpp::wait_for_message(out, node, "chatter", 1s);
+        if (ret) {
+            RCLCPP_INFO(node->get_logger(), "WaitForMessage: [%s]", out.data.c_str());
+		} else { // timeout or error
+			RCLCPP_INFO(node->get_logger(), "WaitForMessage: cannot receive the message");
+		}
+   	}
+}
+
+
+class TestNode : public rclcpp::Node
+{
+public:
+
+	TestNode()
+	: Node("test_node")
+	{
+		auto callback = [this](const std_msgs::msg::String::SharedPtr msg) -> void
+          {
+            RCLCPP_INFO(this->get_logger(), "Subscription: [%s]", msg->data.c_str());
+          };
+        sub_ = this->create_subscription<std_msgs::msg::String>("chatter", 10, callback);
+	}
+
+	virtual ~TestNode()
+	{
+		// empty
+	}
+
+private:
+	rclcpp::Subscription<std_msgs::msg::String>::SharedPtr sub_;
+};
+
+
+int main(int argc, char * argv[])
+{
+	// initialize node and create subscription on it
+	rclcpp::init(argc, argv);
+	auto node = std::make_shared<TestNode>();
+
+	// create another thread to issue `wait_for_message` with TestNode object
+	std::thread thread_object(wait_for_messages, node);
+
+	// give it 5 sec to make sure `wait_for_message` works
+	std::this_thread::sleep_for(std::chrono::seconds(5));
+
+	// spin the node
+	rclcpp::spin(node);
+	rclcpp::shutdown();
+
+	return 0;
+}