OpenSpace/modules/globebrowsing/cache/memoryawaretilecache.h

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2017                                                               *
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#ifndef __OPENSPACE_MODULE_GLOBEBROWSING___MEMORY_AWARE_TILE_CACHE___H__
#define __OPENSPACE_MODULE_GLOBEBROWSING___MEMORY_AWARE_TILE_CACHE___H__

#include <modules/globebrowsing/tile/tile.h>
#include <modules/globebrowsing/tile/tileindex.h>
#include <modules/globebrowsing/cache/memoryawarelrucache.h>

#include <memory>
#include <mutex>

namespace openspace {
namespace globebrowsing {
namespace cache {

struct ProviderTileKey {
    TileIndex tileIndex;
    unsigned int providerID;

    bool operator==(const ProviderTileKey& r) const {
        return (providerID == r.providerID) &&
            (tileIndex == r.tileIndex);
    }
};

struct ProviderTileHasher {
    /**
    Creates a hash which can be used as key in hash maps.
    First set the bits to be unique for all tiles.
    +-------+------------+-------+------------+
    | USAGE | BIT RANGE  | #BITS | MAX VALUE  |
    +-------+------------+-------+------------+
    | level |   0 -  5   |   5   |         31 |
    |     x |   5 - 35   |  30   | 1073741824 |
    |     y |  35 - 64   |  29   |  536870912 |
    +-------+------------+-------+------------+

    Bits are then shifted depending on the tile provider used.
    */
    unsigned long long operator()(const ProviderTileKey& t) const {
        unsigned long long key = 0;
        key |= static_cast<unsigned long long>(t.tileIndex.level);
        key |= static_cast<unsigned long long>(t.tileIndex.x << 5);
        key |= static_cast<unsigned long long>(t.tileIndex.y << 35);
        // Now the key is unique for all tiles, however not for all tile providers.
        // Add to the key depending on the tile provider to avoid some hash collisions.
        // (All hash collisions can not be avoided due to the limit in 64 bit for the
        // hash key)
        // Idea: make some offset in the place of the bits for the x value. Lesser chance
        // of having different x-value than having different tile provider ids.
        key += static_cast<unsigned long long>(t.providerID << 25);
        return key;
    }
};


/**
 * Singleton class used to cache tiles for all <code>CachingTileProvider</code>s.
 */
class MemoryAwareTileCache {
public:
    static void create(size_t cacheSize);
    static void destroy();

    void clear();
    bool exist(ProviderTileKey key) const;
    Tile get(ProviderTileKey key);
    void put(ProviderTileKey key, Tile tile);
  
    void setMaximumSize(size_t maximumSize);

    static MemoryAwareTileCache& ref();

private:
    /**
     * \param cacheSize is the cache size given in bytes.
     */
    MemoryAwareTileCache(size_t cacheSize);
    ~MemoryAwareTileCache() = default;
    
    static MemoryAwareTileCache* _singleton;
    MemoryAwareLRUCache<ProviderTileKey, Tile, ProviderTileHasher> _tileCache;
	static std::mutex _mutexLock;
};

} // namespace cache
} // namespace globebrowsing
} // namespace openspace

#endif // __OPENSPACE_MODULE_GLOBEBROWSING___MEMORY_AWARE_TILE_CACHE___H__