loop_rate.hpp

// Copyright (c) 2024 Angsa Robotics
//
// 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 NAV2_BEHAVIOR_TREE__UTILS__LOOP_RATE_HPP_
#define NAV2_BEHAVIOR_TREE__UTILS__LOOP_RATE_HPP_
 
#include <memory>
#include <utility>
 
#include "rclcpp/rclcpp.hpp"
#include "behaviortree_cpp/bt_factory.h"
#include "behaviortree_cpp/behavior_tree.h"
 
namespace nav2_behavior_tree
{
 
class LoopRate
{
public:
  LoopRate(
    const rclcpp::Duration & period, BT::Tree * tree,
    rclcpp::Clock::SharedPtr clock)
  : clock_(std::move(clock)), period_(period),
    last_interval_(clock_->now()), tree_(tree)
  {}
 
  // Similar to rclcpp::WallRate::sleep() but using tree_->sleep()
  bool sleep()
  {
    // Time coming into sleep
    auto now = clock_->now();
    // Time of next interval
    auto next_interval = last_interval_ + period_;
    // Detect backwards time flow
    if (now < last_interval_) {
      // Best thing to do is to set the next_interval to now + period
      next_interval = now + period_;
    }
    // Update the interval
    last_interval_ += period_;
    // If the time_to_sleep is negative or zero, don't sleep
    if (next_interval <= now) {
      // If an entire cycle was missed then reset next interval.
      // This might happen if the loop took more than a cycle.
      // Or if time jumps forward.
      if (now > next_interval + period_) {
        last_interval_ = now + period_;
      }
      // Either way do not sleep and return false
      return false;
    }
    // Sleep until the target time, preemptible by emitWakeUpSignal().
    auto wake_up = tree_->wakeUpSignal();
    const bool is_sim_time =
      clock_->get_clock_type() == RCL_ROS_TIME &&
      clock_->ros_time_is_active();
    if (is_sim_time) {
      // Sim time diverges from wall time — poll the target clock in short
      // intervals while remaining interruptible by emitWakeUpSignal().
      while (clock_->now() < next_interval) {
        if (wake_up->waitFor(std::chrono::microseconds(500))) {
          return true;  // preempted
        }
      }
    } else {
      // Steady/system clock agrees with wall time — sleep for the exact
      // remaining duration, still interruptible by emitWakeUpSignal().
      auto remaining = next_interval - clock_->now();
      wake_up->waitFor(
        std::chrono::duration_cast<std::chrono::microseconds>(
          std::chrono::nanoseconds(remaining.nanoseconds())));
    }
    return true;
  }
 
  std::chrono::nanoseconds period() const
  {
    return std::chrono::nanoseconds(period_.nanoseconds());
  }
 
private:
  rclcpp::Clock::SharedPtr clock_;
  rclcpp::Duration period_;
  rclcpp::Time last_interval_;
  BT::Tree * tree_;
};
 
}  // namespace nav2_behavior_tree
 
#endif  // NAV2_BEHAVIOR_TREE__UTILS__LOOP_RATE_HPP_