Robot Operating System——AsyncParametersClient监控Parameters的增删改行为

大纲

同步
- 创建SyncParametersClient
- 设置监控回调
- 回调函数主体
- 测试
- 完整代码
异步
- 创建AsyncParametersClient
- 设置监控回调
- 测试
- 完整代码

在《Robot Operating System——Parameter设置的预处理、校验和成功回调》一文中，我们使用Node::add_post_set_parameters_callback设置一个回调函数，用于在Parameters设置成功后，执行相关后续动作，但是这种行为发生在Node内部。

如果我们希望在Node外部监控Parameters变动，则可以使用SyncParametersClient或者AsyncParametersClient类的on_parameter_event方法设置一个回调函数来监控。

我们分别以同步和异步的方式讲解这个功能。

同步

我们参考的例子是demo_nodes_cpp/src/parameters/parameter_events.cpp。
首先我们创建一个待监控的Node

int main(int argc, char ** argv)
{
  // Force flush of the stdout buffer.
  setvbuf(stdout, NULL, _IONBF, BUFSIZ);

  rclcpp::init(argc, argv);

  auto node = rclcpp::Node::make_shared("parameter_events");

创建SyncParametersClient

然后创建一个该Node的连接客户端，并和服务端进行连接。

  auto parameters_client = std::make_shared<rclcpp::SyncParametersClient>(node);
  while (!parameters_client->wait_for_service(1s)) {
    if (!rclcpp::ok()) {
      RCLCPP_ERROR(node->get_logger(), "Interrupted while waiting for the service. Exiting.");
      return 0;
    }
    RCLCPP_INFO(node->get_logger(), "service not available, waiting again...");
  }

设置监控回调

我们通过SyncParametersClient::on_parameter_event设置监控回调函数。它的入参是是一个rcl_interfaces::msg::ParameterEvent指针，用于表达Parameter变动的事件。

events_received_promise 是一个std::promise，我们通过它让回调函数和主程序之间有通信。如下面代码，当回调执行10次后，promise会被设置以通知主程序退出执行。

  auto events_received_promise = std::make_shared<std::promise<void>>();
  auto events_received_future = events_received_promise->get_future();

  // Setup callback for changes to parameters.
  auto sub = parameters_client->on_parameter_event(
    [node, promise = std::move(events_received_promise)](
      rcl_interfaces::msg::ParameterEvent::UniquePtr event) -> void
    {
      static size_t n_times_called = 0u;
      if (on_parameter_event(std::move(event), node->get_logger())) {
        ++n_times_called;
      }
      if (10u == n_times_called) {
        // This callback will be called 10 times, set the promise when that happens.
        promise->set_value();
      }
    });

回调函数主体

event中包含三种数据：

new_parameters。记录新增的Parameters。
changed_parameters。记录修改的Parameters。
deleted_parameters。记录删除的Parameters。

// /opt/ros/jazzy/include/rcl_interfaces/rcl_interfaces/msg/detail/parameter_event__struct.hpp
  using _new_parameters_type =
    std::vector<rcl_interfaces::msg::Parameter_<ContainerAllocator>, typename std::allocator_traits<ContainerAllocator>::template rebind_alloc<rcl_interfaces::msg::Parameter_<ContainerAllocator>>>;
  _new_parameters_type new_parameters;
  using _changed_parameters_type =
    std::vector<rcl_interfaces::msg::Parameter_<ContainerAllocator>, typename std::allocator_traits<ContainerAllocator>::template rebind_alloc<rcl_interfaces::msg::Parameter_<ContainerAllocator>>>;
  _changed_parameters_type changed_parameters;
  using _deleted_parameters_type =
    std::vector<rcl_interfaces::msg::Parameter_<ContainerAllocator>, typename std::allocator_traits<ContainerAllocator>::template rebind_alloc<rcl_interfaces::msg::Parameter_<ContainerAllocator>>>;
  _deleted_parameters_type deleted_parameters;

在监控函数中，我们会过滤掉新增Parameters中的有关qos_overrides前缀的项目。然后分门别类的把上述三种Parameters打印出来。

bool on_parameter_event(
  rcl_interfaces::msg::ParameterEvent::UniquePtr event, rclcpp::Logger logger)
{
  // TODO(wjwwood): The message should have an operator<<, which would replace all of this.
  std::stringstream ss;
  // ignore qos overrides
  event->new_parameters.erase(
    std::remove_if(
      event->new_parameters.begin(),
      event->new_parameters.end(),
      [](const auto & item) {
        const char * param_override_prefix = "qos_overrides.";
        return std::strncmp(
          item.name.c_str(), param_override_prefix, sizeof(param_override_prefix) - 1) == 0u;
      }),
    event->new_parameters.end());
  if (
    !event->new_parameters.size() && !event->changed_parameters.size() &&
    !event->deleted_parameters.size())
  {
    return false;
  }
  ss << "\nParameter event:\n new parameters:";
  for (auto & new_parameter : event->new_parameters) {
    ss << "\n  " << new_parameter.name;
  }
  ss << "\n changed parameters:";
  for (auto & changed_parameter : event->changed_parameters) {
    ss << "\n  " << changed_parameter.name;
  }
  ss << "\n deleted parameters:";
  for (auto & deleted_parameter : event->deleted_parameters) {
    ss << "\n  " << deleted_parameter.name;
  }
  ss << "\n";
  RCLCPP_INFO(logger, "%s", ss.str().c_str());
  return true;
}

测试

  // Declare parameters that may be set on this node
  node->declare_parameter("foo", 0);
  node->declare_parameter("bar", "");
  node->declare_parameter("baz", 0.);
  node->declare_parameter("foobar", false);

  // Set several different types of parameters.
  auto set_parameters_results = parameters_client->set_parameters(
  {
    rclcpp::Parameter("foo", 2),
    rclcpp::Parameter("bar", "hello"),
    rclcpp::Parameter("baz", 1.45),
    rclcpp::Parameter("foobar", true),
  });

  // Change the value of some of them.
  set_parameters_results = parameters_client->set_parameters(
  {
    rclcpp::Parameter("foo", 3),
    rclcpp::Parameter("bar", "world"),
  });

  // TODO(wjwwood): Create and use delete_parameter

  rclcpp::spin_until_future_complete(node, events_received_future.share());
  rclcpp::shutdown();

  return 0;
}

上面的代码的declare_parameter和set_parameters都会导致监控被执行。这些操作一共10次，这样就会导致回调函数中Promise被设置，进而让rclcpp::spin_until_future_complete退出等待，从而关闭整个程序。
在这里插入图片描述

完整代码

// Copyright 2015 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 <cstring>
#include <future>
#include <memory>
#include <sstream>
#include <utility>

#include "rcl_interfaces/msg/parameter_event.hpp"
#include "rclcpp/rclcpp.hpp"

using namespace std::chrono_literals;

bool on_parameter_event(
  rcl_interfaces::msg::ParameterEvent::UniquePtr event, rclcpp::Logger logger)
{
  // TODO(wjwwood): The message should have an operator<<, which would replace all of this.
  std::stringstream ss;
  // ignore qos overrides
  event->new_parameters.erase(
    std::remove_if(
      event->new_parameters.begin(),
      event->new_parameters.end(),
      [](const auto & item) {
        const char * param_override_prefix = "qos_overrides.";
        return std::strncmp(
          item.name.c_str(), param_override_prefix, sizeof(param_override_prefix) - 1) == 0u;
      }),
    event->new_parameters.end());
  if (
    !event->new_parameters.size() && !event->changed_parameters.size() &&
    !event->deleted_parameters.size())
  {
    return false;
  }
  ss << "\nParameter event:\n new parameters:";
  for (auto & new_parameter : event->new_parameters) {
    ss << "\n  " << new_parameter.name;
  }
  ss << "\n changed parameters:";
  for (auto & changed_parameter : event->changed_parameters) {
    ss << "\n  " << changed_parameter.name;
  }
  ss << "\n deleted parameters:";
  for (auto & deleted_parameter : event->deleted_parameters) {
    ss << "\n  " << deleted_parameter.name;
  }
  ss << "\n";
  RCLCPP_INFO(logger, "%s", ss.str().c_str());
  return true;
}

int main(int argc, char ** argv)
{
  // Force flush of the stdout buffer.
  setvbuf(stdout, NULL, _IONBF, BUFSIZ);

  rclcpp::init(argc, argv);

  auto node = rclcpp::Node::make_shared("parameter_events");

  auto parameters_client = std::make_shared<rclcpp::SyncParametersClient>(node);
  while (!parameters_client->wait_for_service(1s)) {
    if (!rclcpp::ok()) {
      RCLCPP_ERROR(node->get_logger(), "Interrupted while waiting for the service. Exiting.");
      return 0;
    }
    RCLCPP_INFO(node->get_logger(), "service not available, waiting again...");
  }

  auto events_received_promise = std::make_shared<std::promise<void>>();
  auto events_received_future = events_received_promise->get_future();

  // Setup callback for changes to parameters.
  auto sub = parameters_client->on_parameter_event(
    [node, promise = std::move(events_received_promise)](
      rcl_interfaces::msg::ParameterEvent::UniquePtr event) -> void
    {
      static size_t n_times_called = 0u;
      if (on_parameter_event(std::move(event), node->get_logger())) {
        ++n_times_called;
      }
      if (10u == n_times_called) {
        // This callback will be called 10 times, set the promise when that happens.
        promise->set_value();
      }
    });

  // Declare parameters that may be set on this node
  node->declare_parameter("foo", 0);
  node->declare_parameter("bar", "");
  node->declare_parameter("baz", 0.);
  node->declare_parameter("foobar", false);

  // Set several different types of parameters.
  auto set_parameters_results = parameters_client->set_parameters(
  {
    rclcpp::Parameter("foo", 2),
    rclcpp::Parameter("bar", "hello"),
    rclcpp::Parameter("baz", 1.45),
    rclcpp::Parameter("foobar", true),
  });

  // Change the value of some of them.
  set_parameters_results = parameters_client->set_parameters(
  {
    rclcpp::Parameter("foo", 3),
    rclcpp::Parameter("bar", "world"),
  });

  // TODO(wjwwood): Create and use delete_parameter

  rclcpp::spin_until_future_complete(node, events_received_future.share());
  rclcpp::shutdown();

  return 0;
}

异步

我们参考demo_nodes_cpp/src/parameters/parameter_events_async.cpp的实现。

这次我们使用Node的方式来运行监控。

class ParameterEventsAsyncNode : public rclcpp::Node
{
public:
  DEMO_NODES_CPP_PUBLIC
  explicit ParameterEventsAsyncNode(const rclcpp::NodeOptions & options)
  : Node("parameter_events", options)
  {
    setvbuf(stdout, NULL, _IONBF, BUFSIZ);

创建AsyncParametersClient

我们创建一个和本Node连接的AsyncParametersClient对象，并测试其连接。

    // Typically a parameter client is created for a remote node by passing the name of the remote
    // node in the constructor; in this example we create a parameter client for this node itself.
    parameters_client_ = std::make_shared<rclcpp::AsyncParametersClient>(this);

    // Even though this is in the same node, we still have to wait for the
    // service to be available before declaring parameters (otherwise there is
    // a chance we'll miss some events in the callback).
    while (!parameters_client_->wait_for_service(1s)) {
      if (!rclcpp::ok()) {
        RCLCPP_ERROR(this->get_logger(), "interrupted while waiting for the service. exiting.");
        rclcpp::shutdown();
        return;
      }
      RCLCPP_INFO(this->get_logger(), "service not available, waiting again...");
    }

设置监控回调

回调函数和之前介绍的同步模式中的逻辑是一样的，这儿就不赘述了。

    auto on_parameter_event_callback =
      [this](rcl_interfaces::msg::ParameterEvent::UniquePtr event) -> void
      {
        // ignore qos overrides
        event->new_parameters.erase(
          std::remove_if(
            event->new_parameters.begin(),
            event->new_parameters.end(),
            [](const auto & item) {
              const char * param_override_prefix = "qos_overrides.";
              return std::strncmp(
                item.name.c_str(), param_override_prefix, sizeof(param_override_prefix) - 1) == 0u;
            }),
          event->new_parameters.end());
        if (
          !event->new_parameters.size() && !event->changed_parameters.size() &&
          !event->deleted_parameters.size())
        {
          return;
        }
        // TODO(wjwwood): The message should have an operator<<, which would replace all of this.
        std::stringstream ss;
        ss << "\nParameter event:\n new parameters:";
        for (auto & new_parameter : event->new_parameters) {
          ss << "\n  " << new_parameter.name;
        }
        ss << "\n changed parameters:";
        for (auto & changed_parameter : event->changed_parameters) {
          ss << "\n  " << changed_parameter.name;
        }
        ss << "\n deleted parameters:";
        for (auto & deleted_parameter : event->deleted_parameters) {
          ss << "\n  " << deleted_parameter.name;
        }
        ss << "\n";
        RCLCPP_INFO(this->get_logger(), "%s", ss.str().c_str());
      };

    // Setup callback for changes to parameters.
    parameter_event_sub_ = parameters_client_->on_parameter_event(on_parameter_event_callback);

测试

先声明一些Parameters。这个行为也会触发监控函数执行。

    // Declare parameters that may be set on this node
    this->declare_parameter("foo", 0);
    this->declare_parameter("bar", "");
    this->declare_parameter("baz", 0.);
    this->declare_parameter("foobar", false);

后面的测试代码是一个套娃模式。它会先启动一个Timer，执行一次值的设置。由于AsyncParametersClient的set_parameters也是异步的，但是我们可以设置一个完成时执行的回调。在这个回调中，我们再设置一些值，并最终关闭整个Node。


    // Queue a `set_parameters` request as soon as `spin` is called on this node.
    // TODO(dhood): consider adding a "call soon" notion to Node to not require a timer for this.
    timer_ = create_wall_timer(
      200ms,
      [this]() {
        this->queue_first_set_parameter_request();
      });
  }

private:
  // Set several different types of parameters.
  DEMO_NODES_CPP_LOCAL
  void queue_first_set_parameter_request()
  {
    timer_->cancel();  // Prevent another request from being queued by the timer.
    while (!parameters_client_->wait_for_service(1s)) {
      if (!rclcpp::ok()) {
        RCLCPP_ERROR(this->get_logger(), "interrupted while waiting for the service. exiting.");
        rclcpp::shutdown();
        return;
      }
      RCLCPP_INFO(this->get_logger(), "service not available, waiting again...");
    }
    auto response_received_callback = [this](SetParametersResult future) {
        // Check to see if they were set.
        for (auto & result : future.get()) {
          if (!result.successful) {
            RCLCPP_ERROR(this->get_logger(), "Failed to set parameter: %s", result.reason.c_str());
          }
        }
        this->queue_second_set_parameter_request();
      };

    parameters_client_->set_parameters(
      {
        rclcpp::Parameter("foo", 2),
        rclcpp::Parameter("bar", "hello"),
        rclcpp::Parameter("baz", 1.45),
        rclcpp::Parameter("foobar", true),
      }, response_received_callback);
  }

  // Change the value of some of them.
  DEMO_NODES_CPP_LOCAL
  void queue_second_set_parameter_request()
  {
    auto response_received_callback = [this](SetParametersResult future) {
        // Check to see if they were set.
        for (auto & result : future.get()) {
          if (!result.successful) {
            RCLCPP_ERROR(this->get_logger(), "Failed to set parameter: %s", result.reason.c_str());
          }
        }
        // TODO(wjwwood): Create and use delete_parameter

        // Give time for all of the ParameterEvent callbacks to be received.
        timer_ = create_wall_timer(
          100ms,
          []() {
            rclcpp::shutdown();
          });
      };
    parameters_client_->set_parameters(
      {
        rclcpp::Parameter("foo", 3),
        rclcpp::Parameter("bar", "world"),
      }, response_received_callback);
  }

在这里插入图片描述

完整代码

// Copyright 2015 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 <cstring>
#include <memory>
#include <sstream>
#include <vector>

#include "rcl_interfaces/msg/parameter_event.hpp"
#include "rcl_interfaces/msg/set_parameters_result.hpp"
#include "rclcpp/rclcpp.hpp"
#include "rclcpp_components/register_node_macro.hpp"

#include "demo_nodes_cpp/visibility_control.h"

using namespace std::chrono_literals;
using SetParametersResult =
  std::shared_future<std::vector<rcl_interfaces::msg::SetParametersResult>>;
namespace demo_nodes_cpp
{
class ParameterEventsAsyncNode : public rclcpp::Node
{
public:
  DEMO_NODES_CPP_PUBLIC
  explicit ParameterEventsAsyncNode(const rclcpp::NodeOptions & options)
  : Node("parameter_events", options)
  {
    setvbuf(stdout, NULL, _IONBF, BUFSIZ);
    // Typically a parameter client is created for a remote node by passing the name of the remote
    // node in the constructor; in this example we create a parameter client for this node itself.
    parameters_client_ = std::make_shared<rclcpp::AsyncParametersClient>(this);

    auto on_parameter_event_callback =
      [this](rcl_interfaces::msg::ParameterEvent::UniquePtr event) -> void
      {
        // ignore qos overrides
        event->new_parameters.erase(
          std::remove_if(
            event->new_parameters.begin(),
            event->new_parameters.end(),
            [](const auto & item) {
              const char * param_override_prefix = "qos_overrides.";
              return std::strncmp(
                item.name.c_str(), param_override_prefix, sizeof(param_override_prefix) - 1) == 0u;
            }),
          event->new_parameters.end());
        if (
          !event->new_parameters.size() && !event->changed_parameters.size() &&
          !event->deleted_parameters.size())
        {
          return;
        }
        // TODO(wjwwood): The message should have an operator<<, which would replace all of this.
        std::stringstream ss;
        ss << "\nParameter event:\n new parameters:";
        for (auto & new_parameter : event->new_parameters) {
          ss << "\n  " << new_parameter.name;
        }
        ss << "\n changed parameters:";
        for (auto & changed_parameter : event->changed_parameters) {
          ss << "\n  " << changed_parameter.name;
        }
        ss << "\n deleted parameters:";
        for (auto & deleted_parameter : event->deleted_parameters) {
          ss << "\n  " << deleted_parameter.name;
        }
        ss << "\n";
        RCLCPP_INFO(this->get_logger(), "%s", ss.str().c_str());
      };

    // Setup callback for changes to parameters.
    parameter_event_sub_ = parameters_client_->on_parameter_event(on_parameter_event_callback);

    // Even though this is in the same node, we still have to wait for the
    // service to be available before declaring parameters (otherwise there is
    // a chance we'll miss some events in the callback).
    while (!parameters_client_->wait_for_service(1s)) {
      if (!rclcpp::ok()) {
        RCLCPP_ERROR(this->get_logger(), "interrupted while waiting for the service. exiting.");
        rclcpp::shutdown();
        return;
      }
      RCLCPP_INFO(this->get_logger(), "service not available, waiting again...");
    }

    // Declare parameters that may be set on this node
    this->declare_parameter("foo", 0);
    this->declare_parameter("bar", "");
    this->declare_parameter("baz", 0.);
    this->declare_parameter("foobar", false);

    // Queue a `set_parameters` request as soon as `spin` is called on this node.
    // TODO(dhood): consider adding a "call soon" notion to Node to not require a timer for this.
    timer_ = create_wall_timer(
      200ms,
      [this]() {
        this->queue_first_set_parameter_request();
      });
  }

private:
  // Set several different types of parameters.
  DEMO_NODES_CPP_LOCAL
  void queue_first_set_parameter_request()
  {
    timer_->cancel();  // Prevent another request from being queued by the timer.
    while (!parameters_client_->wait_for_service(1s)) {
      if (!rclcpp::ok()) {
        RCLCPP_ERROR(this->get_logger(), "interrupted while waiting for the service. exiting.");
        rclcpp::shutdown();
        return;
      }
      RCLCPP_INFO(this->get_logger(), "service not available, waiting again...");
    }
    auto response_received_callback = [this](SetParametersResult future) {
        // Check to see if they were set.
        for (auto & result : future.get()) {
          if (!result.successful) {
            RCLCPP_ERROR(this->get_logger(), "Failed to set parameter: %s", result.reason.c_str());
          }
        }
        this->queue_second_set_parameter_request();
      };

    parameters_client_->set_parameters(
      {
        rclcpp::Parameter("foo", 2),
        rclcpp::Parameter("bar", "hello"),
        rclcpp::Parameter("baz", 1.45),
        rclcpp::Parameter("foobar", true),
      }, response_received_callback);
  }

  // Change the value of some of them.
  DEMO_NODES_CPP_LOCAL
  void queue_second_set_parameter_request()
  {
    auto response_received_callback = [this](SetParametersResult future) {
        // Check to see if they were set.
        for (auto & result : future.get()) {
          if (!result.successful) {
            RCLCPP_ERROR(this->get_logger(), "Failed to set parameter: %s", result.reason.c_str());
          }
        }
        // TODO(wjwwood): Create and use delete_parameter

        // Give time for all of the ParameterEvent callbacks to be received.
        timer_ = create_wall_timer(
          100ms,
          []() {
            rclcpp::shutdown();
          });
      };
    parameters_client_->set_parameters(
      {
        rclcpp::Parameter("foo", 3),
        rclcpp::Parameter("bar", "world"),
      }, response_received_callback);
  }

  rclcpp::AsyncParametersClient::SharedPtr parameters_client_;
  rclcpp::Subscription<rcl_interfaces::msg::ParameterEvent>::SharedPtr parameter_event_sub_;
  rclcpp::TimerBase::SharedPtr timer_;
};

}  // namespace demo_nodes_cpp

RCLCPP_COMPONENTS_REGISTER_NODE(demo_nodes_cpp::ParameterEventsAsyncNode)