[Galactic backport] wait for message (#1705)

rclcpp/include/rclcpp/wait_for_message.hpp

@@ -0,0 +1,100 @@
+// 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.
+
+#ifndef RCLCPP__WAIT_FOR_MESSAGE_HPP_
+#define RCLCPP__WAIT_FOR_MESSAGE_HPP_
+
+#include <memory>
+#include <string>
+
+#include "rclcpp/node.hpp"
+#include "rclcpp/visibility_control.hpp"
+#include "rclcpp/wait_set.hpp"
+
+namespace rclcpp
+{
+/// Wait for the next incoming message.
+/**
+ * Given an already initialized subscription,
+ * wait for the next incoming message to arrive before the specified timeout.
+ *
+ * \param[out] out is the message to be filled when a new message is arriving.
+ * \param[in] subscription shared pointer to a previously initialized subscription.
+ * \param[in] context shared pointer to a context to watch for SIGINT requests.
+ * \param[in] time_to_wait parameter specifying the timeout before returning.
+ * \return true if a message was successfully received, false if message could not
+ * be obtained or shutdown was triggered asynchronously on the context.
+ */
+template<class MsgT, class Rep = int64_t, class Period = std::milli>
+bool wait_for_message(
+  MsgT & out,
+  std::shared_ptr<rclcpp::Subscription<MsgT>> subscription,
+  std::shared_ptr<rclcpp::Context> context,
+  std::chrono::duration<Rep, Period> time_to_wait = std::chrono::duration<Rep, Period>(-1))
+{
+  auto gc = std::make_shared<rclcpp::GuardCondition>(context);
+  auto shutdown_callback_handle = context->add_on_shutdown_callback(
+    [weak_gc = std::weak_ptr<rclcpp::GuardCondition>{gc}]() {
+      auto strong_gc = weak_gc.lock();
+      if (strong_gc) {
+        strong_gc->trigger();
+      }
+    });
+
+  rclcpp::WaitSet wait_set;
+  wait_set.add_subscription(subscription);
+  wait_set.add_guard_condition(gc);
+  auto ret = wait_set.wait(time_to_wait);
+  if (ret.kind() != rclcpp::WaitResultKind::Ready) {
+    return false;
+  }
+
+  if (wait_set.get_rcl_wait_set().guard_conditions[0]) {
+    return false;
+  }
+
+  rclcpp::MessageInfo info;
+  if (!subscription->take(out, info)) {
+    return false;
+  }
+
+  return true;
+}
+
+/// Wait for the next incoming message.
+/**
+ * Wait for the next incoming message to arrive on a specified topic before the specified timeout.
+ *
+ * \param[out] out is the message to be filled when a new message is arriving.
+ * \param[in] node the node pointer to initialize the subscription on.
+ * \param[in] topic the topic to wait for messages.
+ * \param[in] time_to_wait parameter specifying the timeout before returning.
+ * \return true if a message was successfully received, false if message could not
+ * be obtained or shutdown was triggered asynchronously on the context.
+ */
+template<class MsgT, class Rep = int64_t, class Period = std::milli>
+bool wait_for_message(
+  MsgT & out,
+  rclcpp::Node::SharedPtr node,
+  const std::string & topic,
+  std::chrono::duration<Rep, Period> time_to_wait = std::chrono::duration<Rep, Period>(-1))
+{
+  auto sub = node->create_subscription<MsgT>(topic, 1, [](const std::shared_ptr<MsgT>) {});
+  return wait_for_message<MsgT, Rep, Period>(
+    out, sub, node->get_node_options().context(), time_to_wait);
+}
+
+}  // namespace rclcpp
+
+#endif  // RCLCPP__WAIT_FOR_MESSAGE_HPP_

rclcpp/test/rclcpp/CMakeLists.txt

@@ -565,6 +565,13 @@ if(TARGET test_utilities)
   target_link_libraries(test_utilities ${PROJECT_NAME} mimick)
 endif()
 
+ament_add_gtest(test_wait_for_message test_wait_for_message.cpp)
+if(TARGET test_wait_for_message)
+  ament_target_dependencies(test_wait_for_message
+    "test_msgs")
+  target_link_libraries(test_wait_for_message ${PROJECT_NAME})
+endif()
+
 ament_add_gtest(test_interface_traits test_interface_traits.cpp
   APPEND_LIBRARY_DIRS "${append_library_dirs}")
 if(TARGET test_interface_traits)

rclcpp/test/rclcpp/test_wait_for_message.cpp

@@ -0,0 +1,74 @@
+// 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 <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "rclcpp/node.hpp"
+#include "rclcpp/wait_for_message.hpp"
+
+#include "test_msgs/msg/strings.hpp"
+#include "test_msgs/message_fixtures.hpp"
+
+using namespace std::chrono_literals;
+
+TEST(TestUtilities, wait_for_message) {
+  rclcpp::init(0, nullptr);
+
+  auto node = std::make_shared<rclcpp::Node>("wait_for_message_node");
+
+  using MsgT = test_msgs::msg::Strings;
+  auto pub = node->create_publisher<MsgT>("wait_for_message_topic", 10);
+
+  MsgT out;
+  auto received = false;
+  auto wait = std::async(
+    [&]() {
+      auto ret = rclcpp::wait_for_message(out, node, "wait_for_message_topic", 5s);
+      EXPECT_TRUE(ret);
+      received = true;
+    });
+
+  for (auto i = 0u; i < 10 && received == false; ++i) {
+    pub->publish(*get_messages_strings()[0]);
+    std::this_thread::sleep_for(1s);
+  }
+  ASSERT_TRUE(received);
+  EXPECT_EQ(out, *get_messages_strings()[0]);
+
+  rclcpp::shutdown();
+}
+
+TEST(TestUtilities, wait_for_message_indefinitely) {
+  rclcpp::init(0, nullptr);
+
+  auto node = std::make_shared<rclcpp::Node>("wait_for_message_node2");
+
+  using MsgT = test_msgs::msg::Strings;
+  MsgT out;
+  auto received = false;
+  auto wait = std::async(
+    [&]() {
+      auto ret = rclcpp::wait_for_message(out, node, "wait_for_message_topic" /*, -1 */);
+      EXPECT_TRUE(ret);
+      received = true;
+    });
+
+  rclcpp::shutdown();
+
+  ASSERT_FALSE(received);
+}