AMReX_FabArrayBase.H

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#ifndef BL_FABARRAYBASE_H_
#define BL_FABARRAYBASE_H_
#include <AMReX_Config.H>
 
#include <AMReX_BoxArray.H>
#include <AMReX_DataAllocator.H>
#include <AMReX_DistributionMapping.H>
#include <AMReX_ParallelDescriptor.H>
#include <AMReX_ParallelReduce.H>
#include <AMReX_Periodicity.H>
#include <AMReX_Print.H>
#include <AMReX_Arena.H>
#include <AMReX_Gpu.H>

 
#ifdef AMREX_USE_OMP
#include <omp.h>
#endif
 
#include <cstdint>
#include <ostream>
#include <string>
#include <utility>
 
 
namespace amrex {
 
class MFIter;
class Geometry;
class FArrayBox;
template <typename FAB> class FabFactory;
template <typename FAB> class FabArray;
 
namespace EB2 { class IndexSpace; }

class FabArrayBase
{
    friend class MFIter;
 
    template <class FAB> friend void FillBoundary (Vector<FabArray<FAB>*> const& mf, const Periodicity& period);
 
public:
 
    FabArrayBase () = default;
    ~FabArrayBase () = default;
 
    FabArrayBase (const BoxArray&            bxs,
                  const DistributionMapping& dm,
                  int                        nvar,
                  int                        ngrow);
 
    FabArrayBase (const BoxArray&            bxs,
                  const DistributionMapping& dm,
                  int                        nvar,
                  const IntVect&             ngrow);
 
    FabArrayBase (FabArrayBase&& rhs) noexcept = default;
    FabArrayBase (const FabArrayBase& rhs) = default;
    FabArrayBase& operator= (const FabArrayBase& rhs) = default;
    FabArrayBase& operator= (FabArrayBase&& rhs) = default;
 
    void define (const BoxArray&            bxs,
                 const DistributionMapping& dm,
                 int                        nvar,
                 int                        ngrow);
 
    void define (const BoxArray&            bxs,
                 const DistributionMapping& dm,
                 int                        nvar,
                 const IntVect&             ngrow);

    [[nodiscard]] int nGrow (int direction = 0) const noexcept { return n_grow[direction]; }
 
    [[nodiscard]] IntVect nGrowVect () const noexcept { return n_grow; }

    [[nodiscard]] int nComp () const noexcept { return n_comp; }

    [[nodiscard]] IndexType ixType () const noexcept { return boxarray.ixType(); }
 
    //Return whether this FabArray is empty
    [[nodiscard]] bool empty () const noexcept { return boxarray.empty(); }

    [[nodiscard]] const BoxArray& boxArray () const noexcept { return boxarray; }

    [[nodiscard]] Box box (int K) const noexcept { return boxarray[K]; }

    [[nodiscard]] Box fabbox (int K) const noexcept;

    [[nodiscard]] int size () const noexcept { return static_cast<int>(boxarray.size()); }

    [[nodiscard]] int local_size () const noexcept { return static_cast<int>(indexArray.size()); }

    [[nodiscard]] const Vector<int> &IndexArray () const noexcept { return indexArray; }

    [[nodiscard]] int localindex (int K) const noexcept {
        auto low = std::ranges::lower_bound(indexArray, K);
        if (low != indexArray.end() && *low == K) {
            return static_cast<int>(low - indexArray.begin());
        }
        else {
            return -1;
        }
    }

    [[nodiscard]] const DistributionMapping& DistributionMap () const noexcept { return distributionMap; }

    [[nodiscard]] bool is_nodal () const noexcept;
    [[nodiscard]] bool is_nodal (int dir) const noexcept;
    [[nodiscard]] bool is_cell_centered () const noexcept;

    void setMultiGhost(bool a_multi_ghost) {m_multi_ghost = a_multi_ghost;}
 
    // These are provided for convenience to keep track of how many
    // ghost cells are up to date.  The number of filled ghost cells
    // is updated by FillBoundary and ParallelCopy.
    [[nodiscard]] IntVect nGrowFilled () const noexcept { return n_filled; }
    void setNGrowFilled (IntVect const& ng) noexcept { n_filled = ng; }

    [[nodiscard]] bool isFusingCandidate () const noexcept;

    struct CacheStats
    {
        int         size{0};     
        int         maxsize{0};  
        Long        maxuse{0};   
        Long        nuse{0};     
        Long        nbuild{0};   
        Long        nerase{0};   
        Long        bytes{0};
        Long        bytes_hwm{0};
        std::string name;     
        explicit CacheStats (std::string  name_)
            : name(std::move(name_)) {}
        void recordBuild () noexcept {
            ++size;
            ++nbuild;
            maxsize = std::max(maxsize, size);
        }
        void recordErase (Long n) noexcept {
            // n: how many times the item to be deleted has been used.
            --size;
            ++nerase;
            maxuse = std::max(maxuse, n);
        }
        void recordUse () noexcept { ++nuse; }
        void print () const {
            amrex::Print(Print::AllProcs) << "### " << name << " ###\n"
                                          << "    tot # of builds  : " << nbuild  << "\n"
                                          << "    tot # of erasures: " << nerase  << "\n"
                                          << "    tot # of uses    : " << nuse    << "\n"
                                          << "    max cache size   : " << maxsize << "\n"
                                          << "    max # of uses    : " << maxuse  << "\n";
        }
    };
    struct CopyComTag
    {
        Box dbox;
        Box sbox;
        int dstIndex;
        int srcIndex;
        CopyComTag () noexcept = default;
        CopyComTag (const Box& db, const Box& sb, int didx, int sidx) noexcept
            : dbox(db), sbox(sb), dstIndex(didx), srcIndex(sidx) {}
        bool operator< (const CopyComTag& rhs) const noexcept {
            return (srcIndex < rhs.srcIndex) || ((srcIndex == rhs.srcIndex) && (
                   (sbox.smallEnd() < rhs.sbox.smallEnd()
                               || ((sbox.smallEnd() == rhs.sbox.smallEnd()) && (
                   (dstIndex < rhs.dstIndex) || ((dstIndex == rhs.dstIndex) && (
                   (dbox.smallEnd() < rhs.dbox.smallEnd()))))))));
        }
        //
        // Some typedefs & helper functions used throughout the code.
        //
        using CopyComTagsContainer = std::vector<CopyComTag>;
 
        using MapOfCopyComTagContainers = std::map<int,CopyComTagsContainer>;
    };
    //
    // Some useful typedefs.
    //
    using CopyComTagsContainer = CopyComTag::CopyComTagsContainer;
    using MapOfCopyComTagContainers = CopyComTag::MapOfCopyComTagContainers;
    //
    static Long bytesOfMapOfCopyComTagContainers (const MapOfCopyComTagContainers&);

    struct BDKey {
        BDKey () noexcept = default;
        BDKey (const BoxArray::RefID& baid, const DistributionMapping::RefID& dmid) noexcept
            : m_ba_id(baid), m_dm_id(dmid) {}
        bool operator< (const BDKey& rhs) const noexcept {
            return (m_ba_id < rhs.m_ba_id) ||
                ((m_ba_id == rhs.m_ba_id) && (m_dm_id < rhs.m_dm_id));
        }
        bool operator== (const BDKey& rhs) const noexcept {
            return m_ba_id == rhs.m_ba_id && m_dm_id == rhs.m_dm_id;
        }
        bool operator!= (const BDKey& rhs) const noexcept {
            return m_ba_id != rhs.m_ba_id || m_dm_id != rhs.m_dm_id;
        }
        friend std::ostream& operator<< (std::ostream& os, const BDKey& id);
    private:
        BoxArray::RefID            m_ba_id;
        DistributionMapping::RefID m_dm_id;
    };
 
    [[nodiscard]] BDKey getBDKey () const noexcept {
        return {boxarray.getRefID(), distributionMap.getRefID()};
    }

    void updateBDKey ();
 
    //
    struct TileArray
    {
        Long nuse{-1};
        Vector<int> numLocalTiles;
        Vector<int> indexMap;
        Vector<int> localIndexMap;
        Vector<int> localTileIndexMap;
        Vector<Box> tileArray;
        [[nodiscard]] Long bytes () const;
    };
 
    //
    struct FabComTag
    {
        int fromProc{0};
        int toProc{0};
        int fabIndex{0};
        int fineIndex{0};
        int srcComp{0};
        int destComp{0};
        int nComp{0};
        int face{0};
        int fabArrayId{0};
        int fillBoxId{0};
        int procThatNeedsData{0};
        int procThatHasData{0};
        Box box;
    };

    static AMREX_EXPORT IntVect mfiter_tile_size;

    static AMREX_EXPORT int MaxComp;

    static void Initialize ();
    static void Finalize ();
    static AMREX_EXPORT IntVect comm_tile_size;  
 
    struct FPinfo
    {
        FPinfo (const FabArrayBase& srcfa,
                const FabArrayBase& dstfa,
                const Box&          dstdomain,
                const IntVect&      dstng,
                const BoxConverter& coarsener,
                const Box&          fdomain,
                const Box&          cdomain,
                const EB2::IndexSpace* index_space);
        ~FPinfo ();
        FPinfo (FPinfo const&) = delete;
        FPinfo (FPinfo&&) = delete;
        FPinfo& operator= (FPinfo const&) = delete;
        FPinfo& operator= (FPinfo&&) = delete;
 
        [[nodiscard]] Long bytes () const;
 
        BoxArray            ba_crse_patch;
        BoxArray            ba_fine_patch;
        DistributionMapping dm_patch;
        std::unique_ptr<FabFactory<FArrayBox> > fact_crse_patch;
        std::unique_ptr<FabFactory<FArrayBox> > fact_fine_patch;
        std::unique_ptr<FabArrayBase> keep_crse_patch;
        std::unique_ptr<FabArrayBase> keep_fine_patch;
        //
        BDKey               m_srcbdk;
        BDKey               m_dstbdk;
        Box                 m_dstdomain;
        IntVect             m_dstng;
        std::unique_ptr<BoxConverter> m_coarsener;
        const EB2::IndexSpace* m_index_space = nullptr;
        //
        Long                m_nuse{0};
    };
 
    using FPinfoCache = std::multimap<BDKey,FabArrayBase::FPinfo*>;
    using FPinfoCacheIter = FPinfoCache::iterator;
 
    static FPinfoCache m_TheFillPatchCache;
 
    static CacheStats m_FPinfo_stats;
 
    static const FPinfo& TheFPinfo (const FabArrayBase& srcfa,
                                    const FabArrayBase& dstfa,
                                    const IntVect&      dstng,
                                    const BoxConverter& coarsener,
                                    const Geometry&     fgeom,
                                    const Geometry&     cgeom,
                                    const EB2::IndexSpace*);
 
    void flushFPinfo (bool no_assertion=false) const;

    static void flushFPinfo (const EB2::IndexSpace* ispace);
 
    //
    struct CFinfo
    {
        CFinfo (const FabArrayBase& finefa,
                const Geometry&     finegm,
                const IntVect&      ng,
                bool                include_periodic,
                bool                include_physbndry);
 
        [[nodiscard]] Long bytes () const;
 
        static Box Domain (const Geometry& geom, const IntVect& ng,
                           bool include_periodic, bool include_physbndry);
 
        BoxArray            ba_cfb;
        DistributionMapping dm_cfb;
        Vector<int>          fine_grid_idx; 
        //
        BDKey               m_fine_bdk;
        Box                 m_fine_domain;
        IntVect             m_ng;
        bool                m_include_periodic;
        bool                m_include_physbndry;
        //
        Long                m_nuse{0};
    };
 
    using CFinfoCache = std::multimap<BDKey,FabArrayBase::CFinfo*>;
    using CFinfoCacheIter = CFinfoCache::iterator;
 
    static CFinfoCache m_TheCrseFineCache;
 
    static CacheStats m_CFinfo_stats;
 
    static const CFinfo& TheCFinfo (const FabArrayBase& finefa,
                                    const Geometry&     finegm,
                                    const IntVect&      ng,
                                    bool                include_periodic,
                                    bool                include_physbndry);
 
    void flushCFinfo (bool no_assertion=false) const;
 
    //
    enum CpOp { COPY = 0, ADD = 1 };

    const TileArray* getTileArray (const IntVect& tilesize) const;
 
    // Memory Usage Tags
    struct meminfo {
        Long nbytes = 0L;
        Long nbytes_hwm = 0L;
    };
    static std::map<std::string, meminfo> m_mem_usage;

    static void updateMemUsage (std::string const& tag, Long nbytes, Arena const* ar);

    static void printMemUsage ();

    static Long queryMemUsage (const std::string& tag = std::string("All"));

    static Long queryMemUsageHWM (const std::string& tag = std::string("All"));

    static void pushRegionTag (const char* t);
    static void pushRegionTag (std::string t);
    static void popRegionTag ();
 
    static AMREX_EXPORT std::vector<std::string> m_region_tag;
    struct RegionTag {
        RegionTag (const char* t) : tagged(true) { pushRegionTag(t); }
        RegionTag (const std::string& t) : tagged(true) { pushRegionTag(t); }
        RegionTag (RegionTag const&) = delete;
        RegionTag (RegionTag && rhs) noexcept : tagged(rhs.tagged) { rhs.tagged = false; }
        RegionTag& operator= (RegionTag const&) = delete;
        RegionTag& operator= (RegionTag &&) = delete;
        ~RegionTag () { if (tagged) { popRegionTag(); } }
    private:
        bool tagged = false;
    };
 
//#ifndef AMREX_USE_GPU
//protected:
//#endif

    void clear ();

    const std::vector<bool>& OwnerShip () const noexcept { return ownership; }
    bool isOwner (int li) const noexcept { return ownership[li]; }
 
    //
    // The data ...
    //
    mutable BoxArray    boxarray;
    DistributionMapping distributionMap;
    Vector<int>         indexArray;
    std::vector<bool>   ownership;
    IntVect             n_grow;
    int                 n_comp;
    mutable BDKey       m_bdkey;
    IntVect             n_filled;  // Note that IntVect is zero by default.
    bool                m_multi_ghost = false;
 
    //
    // Tiling
    //
    // We use tile size as the key for the inner map.
 
    using TAMap   = std::map<std::pair<IntVect,IntVect>, TileArray>;
    using TACache = std::map<BDKey, TAMap>;
    //
    static TACache     m_TheTileArrayCache;
    static CacheStats  m_TAC_stats;
    //
    void buildTileArray (const IntVect& tilesize, TileArray& ta) const;
    //
    void flushTileArray (const IntVect& tilesize = IntVect::TheZeroVector(),
                         bool no_assertion=false) const;
    static void flushTileArrayCache (); 
 
    struct CommMetaData
    {
        // The cache of local and send/recv per FillBoundary() or ParallelCopy().
        bool m_threadsafe_loc = false;
        bool m_threadsafe_rcv = false;
        std::unique_ptr<CopyComTagsContainer>      m_LocTags;
        std::unique_ptr<MapOfCopyComTagContainers> m_SndTags;
        std::unique_ptr<MapOfCopyComTagContainers> m_RcvTags;
    };

    void define_fb_metadata (CommMetaData& cmd, const IntVect& nghost, bool cross,
                             const Periodicity& period, bool multi_ghost) const;
 
    //
    struct FB
        : CommMetaData
    {
        FB (const FabArrayBase& fa, const IntVect& nghost,
            bool cross, const Periodicity& period,
            bool enforce_periodicity_only, bool override_sync,
            bool multi_ghost, IntVect const& sumboundary_src_nghost);
 
        std::uint64_t m_id = std::numeric_limits<std::uint64_t>::max();
        IndexType    m_typ;
        IntVect      m_crse_ratio; 
        IntVect      m_ngrow;
        IntVect      m_sb_snghost;
        bool         m_cross;
        bool         m_epo;
        bool         m_override_sync;
        Periodicity  m_period;
        //
        Long         m_nuse{0};
        bool         m_multi_ghost = false;
        //
#if defined(__CUDACC__) && defined (AMREX_USE_CUDA)
        CudaGraph<CopyMemory> m_localCopy;
        CudaGraph<CopyMemory> m_copyToBuffer;
        CudaGraph<CopyMemory> m_copyFromBuffer;
#endif
        //
        [[nodiscard]] Long bytes () const;
    private:
        void define_fb (const FabArrayBase& fa);
        void define_epo (const FabArrayBase& fa);
        void define_os (const FabArrayBase& fa);
        void define_sb (const FabArrayBase& fa);
        void tag_one_box (int krcv, BoxArray const& ba, DistributionMapping const& dm,
                          bool build_recv_tag);
    };
    //
    using FBCache = std::multimap<BDKey,FabArrayBase::FB*>;
    using FBCacheIter = FBCache::iterator;
    //
    static FBCache    m_TheFBCache;
    static CacheStats m_FBC_stats;
    //
    const FB& getFB (const IntVect& nghost, const Periodicity& period,
                     bool cross=false, bool enforce_periodicity_only = false,
                     bool override_sync = false,
                     IntVect const& sumboundary_src_nghost = IntVect(-1)) const;
 
    //
    struct CPC
        : CommMetaData
    {
        CPC (const FabArrayBase& dstfa, const IntVect& dstng,
             const FabArrayBase& srcfa, const IntVect& srcng,
             const Periodicity& period, bool to_ghost_cells_only = false,
             const IntVect& offset = IntVect(0));
        CPC (const BoxArray& dstba, const DistributionMapping& dstdm,
             const Vector<int>& dstidx, const IntVect& dstng,
             const BoxArray& srcba, const DistributionMapping& srcdm,
             const Vector<int>& srcidx, const IntVect& srcng,
             const Periodicity& period, int myproc);
        CPC (const BoxArray& ba, const IntVect& ng,
             const DistributionMapping& dstdm, const DistributionMapping& srcdm);
 
        [[nodiscard]] Long bytes () const;
 
        std::uint64_t m_id = std::numeric_limits<std::uint64_t>::max();
        BDKey       m_srcbdk;
        BDKey       m_dstbdk;
        IntVect     m_srcng;
        IntVect     m_dstng;
        IntVect     m_offset;
        Periodicity m_period;
        bool        m_tgco;
        BoxArray    m_srcba;
        BoxArray    m_dstba;
        //
        Long        m_nuse{0};
 
    private:
        void define (const BoxArray& ba_dst, const DistributionMapping& dm_dst,
                     const Vector<int>& imap_dst,
                     const BoxArray& ba_src, const DistributionMapping& dm_src,
                     const Vector<int>& imap_src,
                     int MyProc = ParallelDescriptor::MyProc());
    };
 
    //
    using CPCache = std::multimap<BDKey,FabArrayBase::CPC*>;
    using CPCacheIter = CPCache::iterator;
    //
    static CPCache    m_TheCPCache;
    static CacheStats m_CPC_stats;
    //
    const CPC& getCPC (const IntVect& dstng, const FabArrayBase& src, const IntVect& srcng,
                       const Periodicity& period, bool to_ghost_cells_only = false,
                       const IntVect& offset = IntVect(0)) const;
 
    //
    struct RB90
        : CommMetaData
    {
        RB90 (const FabArrayBase& fa, const IntVect& nghost, Box const& domain);
        IntVect m_ngrow;
        Box     m_domain;
    private:
        void define (const FabArrayBase& fa);
    };
    //
    using RB90Cache = std::multimap<BDKey,FabArrayBase::RB90*>;
    using RB90CacheIter = RB90Cache::iterator;
    //
    static RB90Cache m_TheRB90Cache;
    //
    const RB90& getRB90 (const IntVect& nghost, const Box& domain) const;
    //
    void flushRB90 (bool no_assertion=false) const; 
    static void flushRB90Cache (); 
 
    //
    struct RB180
        : CommMetaData
    {
        RB180 (const FabArrayBase& fa, const IntVect& nghost, Box const& domain);
        IntVect m_ngrow;
        Box     m_domain;
    private:
        void define (const FabArrayBase& fa);
    };
    //
    using RB180Cache = std::multimap<BDKey,FabArrayBase::RB180*>;
    using RB180CacheIter = RB180Cache::iterator;
    //
    static RB180Cache m_TheRB180Cache;
    //
    const RB180& getRB180 (const IntVect& nghost, const Box& domain) const;
    //
    void flushRB180 (bool no_assertion=false) const; 
    static void flushRB180Cache (); 
 
    //
    struct PolarB
        : CommMetaData
    {
        PolarB (const FabArrayBase& fa, const IntVect& nghost, Box const& domain);
        IntVect m_ngrow;
        Box     m_domain;
    private:
        void define (const FabArrayBase& fa);
    };
    //
    using PolarBCache = std::multimap<BDKey,FabArrayBase::PolarB*>;
    using PolarBCacheIter = PolarBCache::iterator;
    //
    static PolarBCache m_ThePolarBCache;
    //
    const PolarB& getPolarB (const IntVect& nghost, const Box& domain) const;
    //
    void flushPolarB (bool no_assertion=false) const; 
    static void flushPolarBCache (); 
 
#ifdef AMREX_USE_GPU
    //
    struct ParForInfo
    {
        enum class Kind { full, strided, redblack };
        struct RedBlack {};

        ParForInfo (const FabArrayBase& fa, const IntVect& nghost);
        ParForInfo (const FabArrayBase& fa, const IntVect& stride, const IntVect& offset);
        ParForInfo (const FabArrayBase& fa, RedBlack);
        ~ParForInfo ();
 
        int getNBlocksPerBox (int nthreads) const {
            return int((m_ncellsmax+nthreads-1)/nthreads);
        }
        BoxIndexer const* getBoxes () const { return m_boxes; }
 
        ParForInfo () = delete;
        ParForInfo (ParForInfo const&) = delete;
        ParForInfo (ParForInfo &&) = delete;
        void operator= (ParForInfo const&) = delete;
        void operator= (ParForInfo &&) = delete;
 
        BATransformer m_bat;
        Kind m_kind = Kind::full;
        IntVect m_ng;
        IntVect m_stride{1};
        IntVect m_offset{0};
        Long m_ncellsmax = 0;
        BoxIndexer* m_boxes = nullptr;
        char* m_hp = nullptr;
    };

    ParForInfo const& getParForInfo (const IntVect& nghost) const;

    ParForInfo const& getParForInfo (const IntVect& stride, const IntVect& offset) const;

    ParForInfo const& getParForInfoRedBlack () const;
 
    static std::multimap<BDKey,ParForInfo*> m_TheParForCache;
 
    void flushParForInfo (bool no_assertion=false) const; // flushes its own cache
    static void flushParForCache (); // flushes the entire cache
 
#endif
 
    //
    static std::map<BDKey, int> m_BD_count;
    //
    void clearThisBD (bool no_assertion=false) const;
    //
    void addThisBD ();
    //
    struct FabArrayStats
    {
        int  num_fabarrays{0};
        int  max_num_fabarrays{0};
        int  max_num_boxarrays{0};
        int  max_num_ba_use{1};
        Long num_build{0};
 
        void recordBuild () noexcept {
            ++num_fabarrays;
            ++num_build;
            max_num_fabarrays = std::max(max_num_fabarrays, num_fabarrays);
        }
        void recordDelete () noexcept {
            --num_fabarrays;
        }
        void recordMaxNumBoxArrays (int n) noexcept {
            max_num_boxarrays = std::max(max_num_boxarrays, n);
        }
        void recordMaxNumBAUse (int n) noexcept {
            max_num_ba_use = std::max(max_num_ba_use, n);
        }
        void print () const {
            amrex::Print(Print::AllProcs) << "### FabArray ###\n"
                                          << "    tot # of builds       : " << num_build         << "\n"
                                          << "    max # of FabArrays    : " << max_num_fabarrays << "\n"
                                          << "    max # of BoxArrays    : " << max_num_boxarrays << "\n"
                                          << "    max # of BoxArray uses: " << max_num_ba_use    << "\n";
        }
    };
    static AMREX_EXPORT FabArrayStats m_FA_stats;
 
    static AMREX_EXPORT bool m_alloc_single_chunk;

    [[nodiscard]] static bool getAllocSingleChunk () { return m_alloc_single_chunk; }

    [[nodiscard]] static std::uint64_t getNextCommMetaDataId ();
 
private:
 
    void flushFB (bool no_assertion=false) const; 
    static void flushFBCache (); 
 
    void flushCPC (bool no_assertion=false) const; 
    static void flushCPCache (); 
};

namespace detail {
    class SingleChunkArena final
        : public Arena
    {
    public:
        SingleChunkArena (Arena* a_arena, std::size_t a_size);
        ~SingleChunkArena () override;
 
        SingleChunkArena () = delete;
        SingleChunkArena (const SingleChunkArena& rhs) = delete;
        SingleChunkArena (SingleChunkArena&& rhs) = delete;
        SingleChunkArena& operator= (const SingleChunkArena& rhs) = delete;
        SingleChunkArena& operator= (SingleChunkArena&& rhs) = delete;
 
        [[nodiscard]] void* alloc (std::size_t sz) override;
        void free (void* pt) override;
 
        // isDeviceAccessible and isHostAccessible can both be true.
        [[nodiscard]] bool isDeviceAccessible () const override;
        [[nodiscard]] bool isHostAccessible () const override;
 
        [[nodiscard]] bool isManaged () const override;
        [[nodiscard]] bool isDevice () const override;
        [[nodiscard]] bool isPinned () const override;
 
        [[nodiscard]] void* data () const noexcept { return (void*) m_root; }
 
    private:
        DataAllocator m_dallocator;
        char* m_root = nullptr;
        char* m_free = nullptr;
        std::size_t m_size = 0;
    };
}

[[nodiscard]] int nComp (FabArrayBase const& fa);
[[nodiscard]] IntVect nGrowVect (FabArrayBase const& fa);
[[nodiscard]] BoxArray const& boxArray (FabArrayBase const& fa);
[[nodiscard]] DistributionMapping const& DistributionMap (FabArrayBase const& fa);
 
#ifdef BL_USE_MPI
bool CheckRcvStats (Vector<MPI_Status>& recv_stats, const Vector<std::size_t>& recv_size, int tag);
#endif
 
std::ostream& operator<< (std::ostream& os, const FabArrayBase::BDKey& id);
 
}
 
#endif