OpenTTD/src/pathfinder/yapf/yapf_costcache.hpp

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file yapf_costcache.hpp Caching of segment costs. */

#ifndef YAPF_COSTCACHE_HPP
#define YAPF_COSTCACHE_HPP

#include "../../misc/hashtable.hpp"
#include "../../tile_type.h"
#include "../../track_type.h"

/**
 * CYapfSegmentCostCacheNoneT - the formal only yapf cost cache provider that implements
 * PfNodeCacheFetch(). Used when nodes don't have CachedData
 * defined (they don't count with any segment cost caching).
 */
template <class Types>
class CYapfSegmentCostCacheNoneT
{
public:
	typedef typename Types::Tpf Tpf; ///< the pathfinder class (derived from THIS class)
	typedef typename Types::NodeList::Item Node; ///< this will be our node type

	/**
	 * Called by YAPF to attach cached or local segment cost data to the given node.
	 *  @return true if globally cached data were used or false if local data was used
	 */
	inline bool PfNodeCacheFetch(Node &)
	{
		return false;
	}
};

/**
 * Base class for segment cost cache providers. Contains global counter
 *  of track layout changes and static notification function called whenever
 *  the track layout changes. It is implemented as base class because it needs
 *  to be shared between all rail YAPF types (one shared counter, one notification
 *  function.
 */
struct CSegmentCostCacheBase
{
	static int   s_rail_change_counter;

	static void NotifyTrackLayoutChange(TileIndex, Track)
	{
		s_rail_change_counter++;
	}
};


/**
 * CSegmentCostCacheT - template class providing hash-map and storage (heap)
 *  of Tsegment structures. Each rail node contains pointer to the segment
 *  that contains cached (or non-cached) segment cost information. Nodes can
 *  differ by key type, but they use the same segment type. Segment key should
 *  be always the same (TileIndex + DiagDirection) that represent the beginning
 *  of the segment (origin tile and exit-dir from this tile).
 *  Different CYapfCachedCostT types can share the same type of CSegmentCostCacheT.
 *  Look at CYapfRailSegment (yapf_node_rail.hpp) for the segment example
 */
template <class Tsegment>
struct CSegmentCostCacheT : public CSegmentCostCacheBase {
	static constexpr int HASH_BITS = 14;

	using Key = typename Tsegment::Key; ///< key to hash table

	HashTable<Tsegment, HASH_BITS> map;
	std::deque<Tsegment> heap;

	inline CSegmentCostCacheT() {}

	/** flush (clear) the cache */
	inline void Flush()
	{
		this->map.Clear();
		this->heap.clear();
	}

	inline Tsegment &Get(Key &key, bool *found)
	{
		Tsegment *item = this->map.Find(key);
		if (item == nullptr) {
			*found = false;
			item = &this->heap.emplace_back(key);
			this->map.Push(*item);
		} else {
			*found = true;
		}
		return *item;
	}
};

/**
 * CYapfSegmentCostCacheGlobalT - the yapf cost cache provider that adds the segment cost
 *  caching functionality to yapf. Using this class as base of your will provide the global
 *  segment cost caching services for your Nodes.
 */
template <class Types>
class CYapfSegmentCostCacheGlobalT {
public:
	typedef typename Types::Tpf Tpf; ///< the pathfinder class (derived from THIS class)
	typedef typename Types::NodeList::Item Node; ///< this will be our node type
	typedef typename Node::Key Key; ///< key to hash tables
	typedef typename Node::CachedData CachedData;
	typedef typename CachedData::Key CacheKey;
	typedef CSegmentCostCacheT<CachedData> Cache;
	using LocalCache = std::deque<CachedData>;

protected:
	Cache &global_cache;
	LocalCache local_cache;

	inline CYapfSegmentCostCacheGlobalT() : global_cache(stGetGlobalCache()) {};

	/** to access inherited path finder */
	inline Tpf &Yapf()
	{
		return *static_cast<Tpf *>(this);
	}

	inline static Cache &stGetGlobalCache()
	{
		static int last_rail_change_counter = 0;
		static Cache C;

		/* delete the cache sometimes... */
		if (last_rail_change_counter != Cache::s_rail_change_counter) {
			last_rail_change_counter = Cache::s_rail_change_counter;
			C.Flush();
		}
		return C;
	}

public:
	/**
	 * Called by YAPF to attach cached or local segment cost data to the given node.
	 *  @return true if globally cached data were used or false if local data was used
	 */
	inline bool PfNodeCacheFetch(Node &n)
	{
		CacheKey key(n.GetKey());

		if (!Yapf().CanUseGlobalCache(n)) {
			Yapf().ConnectNodeToCachedData(n, this->local_cache.emplace_back(key));
			return false;
		}

		bool found;
		CachedData &item = this->global_cache.Get(key, &found);
		Yapf().ConnectNodeToCachedData(n, item);
		return found;
	}
};

#endif /* YAPF_COSTCACHE_HPP */