ForwardQueue.h

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// Authors: Marlin Strub
 
#ifndef OMPL_GEOMETRIC_PLANNERS_INFORMEDTREES_EITSTAR_FORWARD_QUEUE_
#define OMPL_GEOMETRIC_PLANNERS_INFORMEDTREES_EITSTAR_FORWARD_QUEUE_
 
#include <array>
#include <map>
#include <utility>
#include <vector>
 
#include "ompl/base/Cost.h"
#include "ompl/base/samplers/InformedStateSampler.h"
#include "ompl/datastructures/BinaryHeap.h"
#include "ompl/datastructures/NearestNeighbors.h"
 
#include "ompl/geometric/planners/informedtrees/eitstar/Direction.h"
#include "ompl/geometric/planners/informedtrees/eitstar/Edge.h"
#include "ompl/geometric/planners/informedtrees/eitstar/Vertex.h"
 
#include <unordered_map>
 
namespace ompl
{
    namespace geometric
    {
        namespace eitstar
        {
            struct pair_hash
            {
                std::size_t operator()(const std::pair<std::size_t, std::size_t> &k) const
                {
                    // This method to combine hashes is the same as boost::hash_combine
                    // https://www.boost.org/doc/libs/1_67_0/boost/container_hash/hash.hpp
                    // For a discussion see e.g. https://stackoverflow.com/a/35991300
                    std::hash<std::size_t> hasher;
 
                    std::size_t seed = hasher(k.first);
                    seed ^= hasher(k.second) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
 
                    return seed;
                }
            };
 
            class ForwardQueue
            {
            public:
                ForwardQueue(const std::shared_ptr<const ompl::base::OptimizationObjective> &objective,
                             const std::shared_ptr<const ompl::base::StateSpace> &space);

                ~ForwardQueue() = default;

                bool empty() const;

                std::size_t size() const;

                void insertOrUpdate(const Edge &edge);

                void insertOrUpdate(const std::vector<Edge> &edges);

                void remove(const Edge &edge);

                void updateIfExists(const Edge &edge);

                Edge peek(double suboptimalityFactor);

                Edge pop(double suboptimalityFactor);

                ompl::base::Cost getLowerBoundOnOptimalSolutionCost() const;

                bool containsOpenTargets(std::size_t reverseSearchTag) const;

                void clear();

                std::vector<Edge> getEdges() const;

                void rebuild();

                unsigned int getMinEffortToCome() const;

                std::size_t estimateEffort(const Edge &edge) const;
 
            private:
                struct EdgeKeys
                {
                    EdgeKeys(const ompl::base::Cost &lowerBound, const ompl::base::Cost &estimated,
                             const std::size_t effort)
                      : lowerBoundCost(lowerBound), estimatedCost(estimated), estimatedEffort(effort) {};
                    ompl::base::Cost lowerBoundCost;
                    ompl::base::Cost estimatedCost;
                    std::size_t estimatedEffort;
                };

                std::pair<EdgeKeys, Edge> makeElement(const Edge &edge) const;
 
                using Container =
                    std::unordered_map<std::pair<std::size_t, std::size_t>, std::pair<EdgeKeys, Edge>, pair_hash>;

                Container::const_iterator getFrontIter(double suboptimalityFactor);

                inline std::pair<EdgeKeys, Edge> &get(Container::iterator &it) const
                {
                    return it->second;
                }

                inline const std::pair<EdgeKeys, Edge> &get(Container::const_iterator &it) const
                {
                    return it->second;
                }

                Container::iterator getBestCostEstimateEdge();

                Container::iterator getLowerBoundCostEdge();

                Container::const_iterator getLowerBoundCostEdge() const;

                Container::const_iterator getBestCostEstimateEdge() const;

                ompl::base::Cost inflateCost(const ompl::base::Cost &cost, double factor) const;

                ompl::base::Cost estimateCost(const Edge &edge) const;

                ompl::base::Cost lowerBoundCost(const Edge &edge) const;

                std::shared_ptr<const ompl::base::OptimizationObjective> objective_;

                std::shared_ptr<const ompl::base::StateSpace> space_;

                Container queue_{};

                Container::const_iterator front_;

                const bool cacheQueueLookup_ = true;

                bool modifiedQueue_ = true;

                mutable unsigned int cachedMinEdgeEffort_{0u};
            };
        }  // namespace eitstar
 
    }  // namespace geometric
 
}  // namespace ompl
 
#endif  // OMPL_GEOMETRIC_PLANNERS_INFORMEDTREES_EITSTAR_FORWARD_QUEUE_