Add an example about how to use wait_for_all_acked (#316)

Signed-off-by: Barry Xu <[email protected]>

rclcpp/topics/minimal_publisher/CMakeLists.txt

@@ -26,6 +26,9 @@ ament_target_dependencies(publisher_member_function_with_type_adapter rclcpp std
 add_executable(publisher_member_function_with_unique_network_flow_endpoints member_function_with_unique_network_flow_endpoints.cpp)
 ament_target_dependencies(publisher_member_function_with_unique_network_flow_endpoints rclcpp std_msgs)
 
+add_executable(publisher_wait_for_all_acked member_function_with_wait_for_all_acked.cpp)
+ament_target_dependencies(publisher_wait_for_all_acked rclcpp std_msgs)
+
 add_executable(publisher_not_composable not_composable.cpp)
 ament_target_dependencies(publisher_not_composable rclcpp std_msgs)
 
@@ -34,6 +37,7 @@ install(TARGETS
   publisher_member_function
   publisher_member_function_with_type_adapter
   publisher_member_function_with_unique_network_flow_endpoints
+  publisher_wait_for_all_acked
   publisher_not_composable
   DESTINATION lib/${PROJECT_NAME}
 )

rclcpp/topics/minimal_publisher/member_function_with_wait_for_all_acked.cpp

@@ -0,0 +1,94 @@
+// Copyright 2021 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 <chrono>
+#include <functional>
+#include <cinttypes>
+#include <memory>
+#include <string>
+
+#include "rclcpp/rclcpp.hpp"
+#include "std_msgs/msg/string.hpp"
+
+using namespace std::chrono_literals;
+
+/* This example shows how to use wait_for_all_acked for the publisher */
+
+class MinimalPublisher : public rclcpp::Node
+{
+public:
+  MinimalPublisher()
+  : Node("minimal_publisher_with_wait_for_all_acked"),
+    count_(0),
+    wait_timeout_(300)
+  {
+    // publisher must set reliable mode
+    publisher_ = this->create_publisher<std_msgs::msg::String>(
+      "topic",
+      rclcpp::QoS(10).reliable());
+
+    // call wait_for_all_acked before shutdown
+    using rclcpp::contexts::get_global_default_context;
+    get_global_default_context()->add_pre_shutdown_callback(
+      [this]() {
+        this->timer_->cancel();
+        this->wait_for_all_acked();
+      });
+
+    timer_ = this->create_wall_timer(
+      500ms, std::bind(&MinimalPublisher::timer_callback, this));
+  }
+
+private:
+  void wait_for_all_acked()
+  {
+    // Confirm all subscribers receive sent messages.
+    // Note that if no subscription is connected, wait_for_all_acked() always return true.
+    if (publisher_->wait_for_all_acked(wait_timeout_)) {
+      RCLCPP_INFO(
+        this->get_logger(),
+        "All subscribers acknowledge messages");
+    } else {
+      RCLCPP_INFO(
+        this->get_logger(),
+        "Not all subscribers acknowledge messages during %" PRId64 " ms",
+        static_cast<int64_t>(wait_timeout_.count()));
+    }
+  }
+
+  void timer_callback()
+  {
+    auto message = std_msgs::msg::String();
+    message.data = "Hello, world! " + std::to_string(count_++);
+    RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", message.data.c_str());
+    publisher_->publish(message);
+
+    // After sending some messages, you can call wait_for_all_acked() to confirm all subscribers
+    // acknowledge messages.
+  }
+  rclcpp::TimerBase::SharedPtr timer_;
+  rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;
+  size_t count_;
+  std::chrono::milliseconds wait_timeout_;
+};
+
+int main(int argc, char * argv[])
+{
+  rclcpp::init(argc, argv);
+
+  auto publisher = std::make_shared<MinimalPublisher>();
+  rclcpp::spin(publisher);
+  rclcpp::shutdown();
+
+  return 0;
+}