pop_from_queue.hpp

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/*  Copyright (C) 2022 Davide Faconti -  All Rights Reserved
*
*   Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"),
*   to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
*   and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
*   The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
*
*   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
*   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
*   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
 
#pragma once
 
#include <list>
#include <mutex>
#include "behaviortree_cpp/action_node.h"
#include "behaviortree_cpp/decorator_node.h"
 
namespace BT
{
 
template <typename T>
struct ProtectedQueue
{
  std::list<T> items;
  std::mutex mtx;
};
 
/*
 * Few words about why we represent the queue as std::shared_ptr<ProtectedQueue>:
 *
 * Since we will pop from the queue, the fact that the blackboard uses
 * a value semantic is not very convenient, since it would oblige us to
 * copy the entire std::list from the BB and than copy again a new one with one less element.
 *
 * We avoid this using reference semantic (wrapping the object in a shared_ptr).
 * Unfortunately, remember that this makes our access to the list not thread-safe!
 * This is the reason why we add a mutex to be used when modyfying the ProtectedQueue::items
 *
 * */
 
template <typename T>
class PopFromQueue : public SyncActionNode
{
public:
  PopFromQueue(const std::string& name, const NodeConfig& config)
    : SyncActionNode(name, config)
  {}
 
  NodeStatus tick() override
  {
    std::shared_ptr<ProtectedQueue<T>> queue;
    if(getInput("queue", queue) && queue)
    {
      std::unique_lock<std::mutex> lk(queue->mtx);
      auto& items = queue->items;
 
      if(items.empty())
      {
        return NodeStatus::FAILURE;
      }
      else
      {
        T val = items.front();
        items.pop_front();
        setOutput("popped_item", val);
        return NodeStatus::SUCCESS;
      }
    }
    else
    {
      return NodeStatus::FAILURE;
    }
  }
 
  static PortsList providedPorts()
  {
    return { InputPort<std::shared_ptr<ProtectedQueue<T>>>("queue"), OutputPort<T>("poppe"
                                                                                   "d_"
                                                                                   "ite"
                                                                                   "m") };
  }
};
 
template <typename T>
class QueueSize : public SyncActionNode
{
public:
  QueueSize(const std::string& name, const NodeConfig& config)
    : SyncActionNode(name, config)
  {}
 
  NodeStatus tick() override
  {
    std::shared_ptr<ProtectedQueue<T>> queue;
    if(getInput("queue", queue) && queue)
    {
      std::unique_lock<std::mutex> lk(queue->mtx);
      auto& items = queue->items;
 
      if(items.empty())
      {
        return NodeStatus::FAILURE;
      }
      else
      {
        setOutput("size", int(items.size()));
        return NodeStatus::SUCCESS;
      }
    }
    return NodeStatus::FAILURE;
  }
 
  static PortsList providedPorts()
  {
    return { InputPort<std::shared_ptr<ProtectedQueue<T>>>("queue"),
             OutputPort<int>("size") };
  }
};
 
}  // namespace BT