First step towards modernizing the rt publisher (backport #210) (#233)

Co-authored-by: Lennart Nachtigall <[email protected]>

include/realtime_tools/realtime_publisher.hpp

@@ -49,27 +49,39 @@
 
 namespace realtime_tools
 {
-template <class Msg>
+template <class MessageT>
 class RealtimePublisher
 {
-private:
-  using PublisherSharedPtr = typename rclcpp::Publisher<Msg>::SharedPtr;
-
 public:
+  /// Provide various typedefs to resemble the rclcpp::Publisher type
+  using PublisherType = rclcpp::Publisher<MessageT>;
+  using PublisherSharedPtr = typename rclcpp::Publisher<MessageT>::SharedPtr;
+
+  using PublishedType = typename rclcpp::TypeAdapter<MessageT>::custom_type;
+  using ROSMessageType = typename rclcpp::TypeAdapter<MessageT>::ros_message_type;
+
+  RCLCPP_SMART_PTR_DEFINITIONS(RealtimePublisher<MessageT>)
+
   /// The msg_ variable contains the data that will get published on the ROS topic.
-  Msg msg_;
+  MessageT msg_;
 
   /**  \brief Constructor for the realtime publisher
    *
    * \param publisher the publisher to wrap
    */
   explicit RealtimePublisher(PublisherSharedPtr publisher)
-  : publisher_(publisher), is_running_(false), keep_running_(true), turn_(LOOP_NOT_STARTED)
+  : publisher_(publisher), is_running_(false), keep_running_(true), turn_(State::LOOP_NOT_STARTED)
   {
     thread_ = std::thread(&RealtimePublisher::publishingLoop, this);
   }
 
-  RealtimePublisher() : is_running_(false), keep_running_(false), turn_(LOOP_NOT_STARTED) {}
+  [[deprecated(
+    "Use constructor with rclcpp::Publisher<T>::SharedPtr instead - this class does not make sense "
+    "without a real publisher")]]
+  RealtimePublisher()
+  : is_running_(false), keep_running_(false), turn_(State::LOOP_NOT_STARTED)
+  {
+  }
 
   /// Destructor
   ~RealtimePublisher()
@@ -101,7 +113,7 @@ class RealtimePublisher
   bool trylock()
   {
     if (msg_mutex_.try_lock()) {
-      if (turn_ == REALTIME) {
+      if (turn_ == State::REALTIME) {
         return true;
       } else {
         msg_mutex_.unlock();
@@ -112,6 +124,23 @@ class RealtimePublisher
     }
   }
 
+  /**  \brief Try to get the data lock from realtime and publish the given message
+   *
+   * Tries to gain unique access to msg_ variable. If this succeeds
+   * update the msg_ variable and call unlockAndPublish
+   * @return false in case no lock for the realtime variable could be acquired
+   */
+  bool tryPublish(const MessageT & msg)
+  {
+    if (!trylock()) {
+      return false;
+    }
+
+    msg_ = msg;
+    unlockAndPublish();
+    return true;
+  }
+
   /**  \brief Unlock the msg_ variable
    *
    * After a successful trylock and after the data is written to the mgs_
@@ -120,7 +149,7 @@ class RealtimePublisher
    */
   void unlockAndPublish()
   {
-    turn_ = NON_REALTIME;
+    turn_ = State::NON_REALTIME;
     unlock();
   }
 
@@ -163,10 +192,10 @@ class RealtimePublisher
   void publishingLoop()
   {
     is_running_ = true;
-    turn_ = REALTIME;
+    turn_ = State::REALTIME;
 
     while (keep_running_) {
-      Msg outgoing;
+      MessageT outgoing;
 
       // Locks msg_ and copies it
 
@@ -176,7 +205,7 @@ class RealtimePublisher
       lock();
 #endif
 
-      while (turn_ != NON_REALTIME && keep_running_) {
+      while (turn_ != State::NON_REALTIME && keep_running_) {
 #ifdef NON_POLLING
         updated_cond_.wait(lock_);
 #else
@@ -186,7 +215,7 @@ class RealtimePublisher
 #endif
       }
       outgoing = msg_;
-      turn_ = REALTIME;
+      turn_ = State::REALTIME;
 
       unlock();
 
@@ -210,12 +239,12 @@ class RealtimePublisher
   std::condition_variable updated_cond_;
 #endif
 
-  enum { REALTIME, NON_REALTIME, LOOP_NOT_STARTED };
-  std::atomic<int> turn_;  // Who's turn is it to use msg_?
+  enum class State : int { REALTIME, NON_REALTIME, LOOP_NOT_STARTED };
+  std::atomic<State> turn_;  // Who's turn is it to use msg_?
 };
 
-template <class Msg>
-using RealtimePublisherSharedPtr = std::shared_ptr<RealtimePublisher<Msg>>;
+template <class MessageT>
+using RealtimePublisherSharedPtr = std::shared_ptr<RealtimePublisher<MessageT>>;
 
 }  // namespace realtime_tools
 #endif  // REALTIME_TOOLS__REALTIME_PUBLISHER_HPP_

test/realtime_publisher_tests.cpp

@@ -91,3 +91,44 @@ TEST(RealtimePublisher, rt_publish)
   EXPECT_STREQ(expected_msg, str_callback.msg_.string_value.c_str());
   rclcpp::shutdown();
 }
+
+TEST(RealtimePublisher, rt_try_publish)
+{
+  rclcpp::init(0, nullptr);
+  const size_t ATTEMPTS = 10;
+  const std::chrono::milliseconds DELAY(250);
+
+  const char * expected_msg = "Hello World";
+  auto node = std::make_shared<rclcpp::Node>("construct_move_destruct");
+  rclcpp::QoS qos(10);
+  qos.reliable().transient_local();
+  auto pub = node->create_publisher<StringMsg>("~/rt_publish", qos);
+  RealtimePublisher<StringMsg> rt_pub(pub);
+
+  // try publish a latched message
+  bool publish_success = false;
+  for (std::size_t i = 0; i < ATTEMPTS; ++i) {
+    StringMsg msg;
+    msg.string_value = expected_msg;
+
+    if (rt_pub.tryPublish(msg)) {
+      publish_success = true;
+      break;
+    }
+    std::this_thread::sleep_for(DELAY);
+  }
+  ASSERT_TRUE(publish_success);
+
+  // make sure subscriber gets it
+  StringCallback str_callback;
+
+  auto sub = node->create_subscription<StringMsg>(
+    "~/rt_publish", qos,
+    std::bind(&StringCallback::callback, &str_callback, std::placeholders::_1));
+  for (size_t i = 0; i < ATTEMPTS && str_callback.msg_.string_value.empty(); ++i) {
+    rclcpp::spin_some(node);
+    std::this_thread::sleep_for(DELAY);
+  }
+  EXPECT_STREQ(expected_msg, str_callback.msg_.string_value.c_str());
+  rclcpp::shutdown();
+}

test/realtime_publisher_tests_non_polling.cpp

@@ -93,3 +93,44 @@ TEST(RealtimePublisherNonPolling, rt_publish)
   EXPECT_STREQ(expected_msg, str_callback.msg_.string_value.c_str());
   rclcpp::shutdown();
 }
+
+TEST(RealtimePublisher, rt_try_publish)
+{
+  rclcpp::init(0, nullptr);
+  const size_t ATTEMPTS = 10;
+  const std::chrono::milliseconds DELAY(250);
+
+  const char * expected_msg = "Hello World";
+  auto node = std::make_shared<rclcpp::Node>("construct_move_destruct");
+  rclcpp::QoS qos(10);
+  qos.reliable().transient_local();
+  auto pub = node->create_publisher<StringMsg>("~/rt_publish", qos);
+  RealtimePublisher<StringMsg> rt_pub(pub);
+
+  // try publish a latched message
+  bool publish_success = false;
+  for (std::size_t i = 0; i < ATTEMPTS; ++i) {
+    StringMsg msg;
+    msg.string_value = expected_msg;
+
+    if (rt_pub.tryPublish(msg)) {
+      publish_success = true;
+      break;
+    }
+    std::this_thread::sleep_for(DELAY);
+  }
+  ASSERT_TRUE(publish_success);
+
+  // make sure subscriber gets it
+  StringCallback str_callback;
+
+  auto sub = node->create_subscription<StringMsg>(
+    "~/rt_publish", qos,
+    std::bind(&StringCallback::callback, &str_callback, std::placeholders::_1));
+  for (size_t i = 0; i < ATTEMPTS && str_callback.msg_.string_value.empty(); ++i) {
+    rclcpp::spin_some(node);
+    std::this_thread::sleep_for(DELAY);
+  }
+  EXPECT_STREQ(expected_msg, str_callback.msg_.string_value.c_str());
+  rclcpp::shutdown();
+}