source: trunk/Mars/mcore/zofits.h@ 17239

/*
 * zofits.h
 *
 *  FACT native compressed FITS writer
 *      Author: lyard
 */

#include "ofits.h"
#include "zfits.h"
#include "Queue.h"
#include "MemoryManager.h"

#ifdef USE_BOOST_THREADS
#include <boost/thread.hpp>
#endif

#ifndef __MARS__
namespace std
{
#else
using namespace std;
#endif

class zofits : public ofits
{
        /// Overriding of the begin() operator to get the smallest item in the list instead of the true begin
        template<class S>
        struct QueueMin : std::list<S>
        {
            typename std::list<S>::iterator begin()
            {
                return min_element(std::list<S>::begin(), std::list<S>::end());
            }
        };

        /// Parameters required to write a tile to disk
        struct WriteTarget
        {
            bool operator < (const WriteTarget& other)
            {
                return tile_num < other.tile_num;
            }

            uint32_t                tile_num; ///< Tile index of the data (to make sure that they are written in the correct order)
            uint32_t                size;    ///<  Size to write
            shared_ptr<MemoryChunk> data;   ///<   Memory block to write
        };

        /// Parameters required to compress a tile of data
        struct CompressionTarget
        {
            shared_ptr<MemoryChunk> src;             ///< Original data
            shared_ptr<MemoryChunk> transposed_src; ///<  Transposed data
            WriteTarget             target;        ///<   Compressed data
            uint32_t                num_rows;     ///<    Number of rows to compress
        };

public:
        /// constructors
        /// @param numTiles how many data groups should be pre-reserved ?
        /// @param rowPerTile how many rows will be grouped together in a single tile
        /// @param maxUsableMem how many bytes of memory can be used by the compression buffers
        zofits(uint32_t numTiles    = fgNumTiles,
               uint32_t rowPerTile  = fgRowPerTile,
               uint64_t maxUsableMem= fgMaxUsableMem) : ofits(),
                                                        fMemPool(0, maxUsableMem),
                                                        fWriteToDiskQueue(bind(&zofits::WriteBufferToDisk, this, placeholders::_1), false)
        {
            InitMemberVariables(numTiles, rowPerTile, maxUsableMem);
            SetNumThreads(fgNumQueues);
        }

        /// @param fname the target filename
        /// @param numTiles how many data groups should be pre-reserved ?
        /// @param rowPerTile how many rows will be grouped together in a single tile
        /// @param maxUsableMem how many bytes of memory can be used by the compression buffers
        zofits(const char* fname,
               uint32_t numTiles    = fgNumTiles,
               uint32_t rowPerTile  = fgRowPerTile,
               uint64_t maxUsableMem= fgMaxUsableMem) : ofits(fname),
                                                        fMemPool(0, maxUsableMem),
                                                        fWriteToDiskQueue(bind(&zofits::WriteBufferToDisk, this, placeholders::_1), false)
        {
            InitMemberVariables(numTiles, rowPerTile, maxUsableMem);
            SetNumThreads(fgNumQueues);
        }

        /// destructors
        virtual ~zofits()
        {
        }

        //initialization of member variables
        /// @param nt number of tiles
        /// @param rpt number of rows per tile
        /// @param maxUsableMem max amount of RAM to be used by the compression buffers
        void InitMemberVariables(const uint32_t nt=0, const uint32_t rpt=0, const uint64_t maxUsableMem=0)
        {
            if (nt == 0)
                throw runtime_error("There must be at least 1 tile of data (0 specified). This is required by the FITS standard. Please try again with num_tile >= 1.");

            fCheckOffset = 0;
            fNumQueues   = 0;

            fNumTiles       = nt;
            fNumRowsPerTile = rpt;

            fBuffer           = NULL;
            fRealRowWidth     = 0;
            fCatalogExtraRows = 0;
            fCatalogOffset    = 0;

            fMaxUsableMem = maxUsableMem;
#ifdef __EXCEPTIONS
            fThreadsException = exception_ptr();
#endif
        }

        /// write the header of the binary table
        /// @param name the name of the table to be created
        /// @return the state of the file
        virtual bool WriteTableHeader(const char* name="DATA")
        {
            reallocateBuffers();

            ofits::WriteTableHeader(name);

            if (fNumQueues != 0)
            {
                //start the compression queues
                for (auto it=fCompressionQueues.begin(); it!= fCompressionQueues.end(); it++)
                    it->start();

                //start the disk writer
                fWriteToDiskQueue.start();
            }

            //mark that no tile has been written so far
            fLatestWrittenTile = -1;

            return good();
        }

        /// open a new file.
        /// @param filename the name of the file
        /// @param Whether or not the name of the extension should be added or not
        void open(const char* filename, bool addEXTNAMEKey=true)
        {
            ofits::open(filename, addEXTNAMEKey);

            //add compression-related header entries
            SetBool( "ZTABLE",   true,            "Table is compressed");
            SetInt(  "ZNAXIS1",  0,               "Width of uncompressed rows");
            SetInt(  "ZNAXIS2",  0,               "Number of uncompressed rows");
            SetInt(  "ZPCOUNT",  0,               "");
            SetInt(  "ZHEAPPTR", 0,               "");
            SetInt(  "ZTILELEN", fNumRowsPerTile, "Number of rows per tile");
            SetInt(  "THEAP",    0,               "");
            SetStr(  "RAWSUM",   "         0",    "Checksum of raw little endian data");
            SetFloat("ZRATIO",   0,               "Compression ratio");

            fCatalogExtraRows = 0;
            fRawSum.reset();
        }

        /// Super method. does nothing as zofits does not know about DrsOffsets
        /// @return the state of the file
        virtual bool WriteDrsOffsetsTable()
        {
            return good();
        }

        /// Returns the number of bytes per uncompressed row
        /// @return number of bytes per uncompressed row
        uint32_t GetBytesPerRow() const
        {
            return fRealRowWidth;
        }

        /// Write the data catalog
        /// @return the state of the file
        bool WriteCatalog()
        {
            const uint32_t one_catalog_row_size = fTable.num_cols*2*sizeof(uint64_t);
            const uint32_t total_catalog_size   = fCatalog.size()*one_catalog_row_size;

            // swap the catalog bytes before writing
            vector<char> swapped_catalog(total_catalog_size);
            uint32_t shift = 0;
            for (auto it=fCatalog.begin(); it!=fCatalog.end(); it++)
            {
                revcpy<sizeof(uint64_t)>(swapped_catalog.data() + shift, (char*)(it->data()), fTable.num_cols*2);
                shift += one_catalog_row_size;
            }

            // first time writing ? remember where we are
            if (fCatalogOffset == 0)
                fCatalogOffset = tellp();

            // remember where we came from
            const off_t where_are_we = tellp();

            // write to disk
            seekp(fCatalogOffset);
            write(swapped_catalog.data(), total_catalog_size);
            if (where_are_we != fCatalogOffset)
                seekp(where_are_we);

            // udpate checksum
            fCatalogSum.reset();
            fCatalogSum.add(swapped_catalog.data(), total_catalog_size);

            return good();
        }

        /// Applies the DrsOffsets calibration to the data. Does nothing as zofits knows nothing about drsoffsets.
        virtual void DrsOffsetCalibrate(char* )
        {

        }

        /// Grows the catalog in case not enough rows were allocated
        void GrowCatalog()
        {
            uint32_t orig_catalog_size = fCatalog.size();

            fCatalog.resize(fCatalog.size()*2);
            for (uint32_t i=orig_catalog_size;i<fCatalog.size(); i++)
            {
                fCatalog[i].resize(fTable.num_cols);
                for (auto it=(fCatalog[i].begin()); it!=fCatalog[i].end(); it++)
                    *it = CatalogEntry(0,0);
            }

            fCatalogExtraRows += orig_catalog_size;
            fNumTiles         += orig_catalog_size;
        }

        /// write one row of data
        /// @param ptr the source buffer
        /// @param the number of bytes to write
        /// @return the state of the file. WARNING: with multithreading, this will most likely be the state of the file before the data is actually written
        bool WriteRow(const void* ptr, size_t cnt, bool = true)
        {
            if (cnt != fRealRowWidth)
            {
#ifdef __EXCEPTIONS
                throw runtime_error("Wrong size of row given to WriteRow");
#else
                gLog << ___err___ << "ERROR - Wrong size of row given to WriteRow" << endl;
                return false;
#endif
            }

            if (fTable.num_rows >= fNumRowsPerTile*fNumTiles)
            {
//                GrowCatalog();
#ifdef __EXCEPTIONS
                throw runtime_error("Maximum number of rows exceeded for this file");
#else
                gLog << ___err___ << "ERROR - Maximum number of rows exceeded for this file" << endl;
                return false;
#endif
            }

            //copy current row to pool or rows waiting for compression
            char* target_location = fBuffer + fRealRowWidth*(fTable.num_rows%fNumRowsPerTile);
            memcpy(target_location, ptr, fRealRowWidth);

            //for now, make an extra copy of the data, for RAWSUM checksuming.
            //Ideally this should be moved to the threads
            //However, because the RAWSUM must be calculated before the tile is transposed, I am not sure whether
            //one extra memcpy per row written is worse than 100 rows checksumed when the tile is full....
            const uint32_t rawOffset = (fTable.num_rows*fRealRowWidth)%4;
            char* buffer = fRawSumBuffer.data() + rawOffset;
            auto ib = fRawSumBuffer.begin();
            auto ie = fRawSumBuffer.rbegin();
            *ib++ = 0;
            *ib++ = 0;
            *ib++ = 0;
            *ib   = 0;

            *ie++ = 0;
            *ie++ = 0;
            *ie++ = 0;
            *ie   = 0;

            memcpy(buffer, ptr, fRealRowWidth);

            fRawSum.add(fRawSumBuffer, false);

            DrsOffsetCalibrate(target_location);

            fTable.num_rows++;

            if (fTable.num_rows % fNumRowsPerTile == 0)
            {
                CompressionTarget compress_target;
                SetNextCompression(compress_target);

                if (fNumQueues == 0)
                { //no worker threads. do everything in-line
                    uint64_t size_to_write = CompressBuffer(compress_target);

                    WriteTarget write_target;
                    write_target.size     = size_to_write;
                    write_target.data   = compress_target.target.data;
                    write_target.tile_num = compress_target.target.tile_num;

                    return WriteBufferToDisk(write_target);
                }
                else
                {
                    //if all queues are empty, use queue 0
                     uint32_t min_index     = 0;
                     uint32_t min_size      = numeric_limits<uint32_t>::max();
                     uint32_t current_index = 0;

                     for (auto it=fCompressionQueues.begin(); it!=fCompressionQueues.end(); it++)
                     {
                         if (it->size() < min_size)
                         {
                             min_index = current_index;
                             min_size = it->size();
                         }
                         current_index++;
                     }

                    if (!fCompressionQueues[min_index].post(compress_target))
                        throw runtime_error("The compression queues are not started. Did you close the file before writing this row ?");
                }
            }

            return good();
        }

        /// update the real number of rows
        void FlushNumRows()
        {
            SetInt("NAXIS2", (fTable.num_rows + fNumRowsPerTile-1)/fNumRowsPerTile);
            SetInt("ZNAXIS2", fTable.num_rows);
            FlushHeader();
        }

        /// Setup the environment to compress yet another tile of data
        /// @param target the struct where to host the produced parameters
        void SetNextCompression(CompressionTarget& target)
        {
            //get space for transposed data
            shared_ptr<MemoryChunk> transposed_data = fMemPool.malloc();

            //fill up write to disk target
            WriteTarget write_target;
            write_target.tile_num = (fTable.num_rows-1)/fNumRowsPerTile;
            write_target.size     = 0;
            write_target.data     = fMemPool.malloc();

            //fill up compression target
            target.src            = fSmartBuffer;
            target.transposed_src = transposed_data;
            target.target         = write_target;
            target.num_rows       = fTable.num_rows;

            //get a new buffer to host the incoming data
            fSmartBuffer = fMemPool.malloc();
            fBuffer      = fSmartBuffer.get()->get();
        }

        /// Shrinks a catalog that is too long to fit into the reserved space at the beginning of the file.
        void ShrinkCatalog()
        {
            //did we write more rows than what the catalog could host ?
            if (fCatalogExtraRows != 0)
            {
                //how many rows can the regular catalog host ?
                const uint32_t max_regular_rows = (fCatalog.size() - fCatalogExtraRows)*fNumRowsPerTile;
                //what's the shrink factor to be applied ?
                const uint32_t shrink_factor = fTable.num_rows/max_regular_rows + ((fTable.num_rows%max_regular_rows) ? 1 : 0);

                //shrink the catalog !
                for (uint32_t i=0; i<fTable.num_rows/fNumRowsPerTile; i+= shrink_factor)
                {//add the elements one by one, so that the empty ones at the end (i.e. fTable.num_rows%shrink_factor) do not create havok
                    const uint32_t target_catalog_row = i/shrink_factor;
                    //move data from current row (i) to target row
                    for (uint32_t j=0; j<fTable.num_cols; j++)
                    {
                        fCatalog[target_catalog_row][j].second = fCatalog[i][j].second;
                        fCatalog[target_catalog_row][j].first  = 0;
                        uint64_t last_size   = fCatalog[i][j].first;
                        uint64_t last_offset = fCatalog[i][j].second;

                        for (uint32_t k=1; k<shrink_factor; k++)
                        {
                           if (fCatalog[i+k][j].second != 0)
                           {
                               fCatalog[target_catalog_row][j].first +=  fCatalog[i+k][j].second - last_offset;
                           }
                           else
                           {
                               fCatalog[target_catalog_row][j].first += last_size;
                               break;
                           }
                           last_size   = fCatalog[i+k][j].first;
                           last_offset = fCatalog[i+k][j].second;
                        }
                    }
                }

                fCatalog.resize(fCatalog.size() - fCatalogExtraRows);

                //update header keywords
                const uint32_t new_num_rows_per_tiles = fNumRowsPerTile*shrink_factor;
                const uint32_t new_num_tiles_written = (fTable.num_rows + new_num_rows_per_tiles-1)/new_num_rows_per_tiles;
                SetInt("THEAP", new_num_tiles_written*2*sizeof(int64_t)*fTable.num_cols);
                SetInt("NAXIS2", new_num_tiles_written);
                SetInt("ZTILELEN", new_num_rows_per_tiles);
                cout << "New num rows per tiles: " << new_num_rows_per_tiles << " shrink factor: " << shrink_factor << endl;
                cout << "Num tiles written: " << new_num_tiles_written << endl;
            }
        }

        /// close an open file.
        /// @return the state of the file
        bool close()
        {
            // stop compression and write threads
            for (auto it=fCompressionQueues.begin(); it != fCompressionQueues.end(); it++)
                it->wait();

            fWriteToDiskQueue.wait();

            if (tellp() < 0)
            {
#ifdef __EXCEPTIONS
                throw runtime_error("Looks like the file has been closed already");
#else
                return false;
#endif
            }

#ifdef __EXCEPTIONS
            //check if something hapenned while the compression threads were working
            if (fThreadsException != exception_ptr())
            {
                //if so, re-throw the exception that was generated
                rethrow_exception(fThreadsException);
            }
#endif

            //write the last tile of data (if any
            if (fTable.num_rows%fNumRowsPerTile != 0)
            {
                CompressionTarget compress_target;
                SetNextCompression(compress_target);

                //set number of threads to zero before calling compressBuffer
                int32_t backup_num_queues = fNumQueues;
                fNumQueues = 0;
                uint64_t size_to_write = CompressBuffer(compress_target);
                fNumQueues = backup_num_queues;

                WriteTarget write_target;
                write_target.size     = size_to_write;
                write_target.data   = compress_target.target.data;
                write_target.tile_num = compress_target.target.tile_num;

                if (!WriteBufferToDisk(write_target))
                    throw runtime_error("Something went wrong while writing the last tile...");
            }

            AlignTo2880Bytes();

            //update header keywords
            SetInt("ZNAXIS1", fRealRowWidth);
            SetInt("ZNAXIS2", fTable.num_rows);

            SetInt("ZHEAPPTR", fCatalog.size()*fTable.num_cols*sizeof(uint64_t)*2);

            const uint32_t total_num_tiles_written = (fTable.num_rows + fNumRowsPerTile-1)/fNumRowsPerTile;
            const uint32_t total_catalog_width     = 2*sizeof(int64_t)*fTable.num_cols;

            SetInt("THEAP",  total_num_tiles_written*total_catalog_width);
            SetInt("NAXIS1", total_catalog_width);
            SetInt("NAXIS2", total_num_tiles_written);

            ostringstream str;
            str << fRawSum.val();
            SetStr("RAWSUM", str.str());

            int64_t heap_size = 0;
            int64_t compressed_offset = 0;

            for (uint32_t i=0; i<total_num_tiles_written; i++)
            {
                compressed_offset += sizeof(TileHeader);
                heap_size         += sizeof(TileHeader);
                for (uint32_t j=0; j<fCatalog[i].size(); j++)
                {
                    heap_size += fCatalog[i][j].first;
                    fCatalog[i][j].second = compressed_offset;
                    compressed_offset += fCatalog[i][j].first;
                    if (fCatalog[i][j].first == 0)
                        fCatalog[i][j].second = 0;
                }
            }

            const float compression_ratio = (float)(fRealRowWidth*fTable.num_rows)/(float)heap_size;
            SetFloat("ZRATIO", compression_ratio);

            //add to the heap size the size of the gap between the catalog and the actual heap
            heap_size += (fCatalog.size() - total_num_tiles_written)*fTable.num_cols*sizeof(uint64_t)*2;

            SetInt("PCOUNT", heap_size, "size of special data area");

            //Just for updating the fCatalogSum value
            WriteCatalog();

            fDataSum += fCatalogSum;

            const Checksum checksm = UpdateHeaderChecksum();

            ofstream::close();

            if ((checksm+fDataSum).valid())
                return true;

            ostringstream sout;
            sout << "Checksum (" << std::hex << checksm.val() << ") invalid.";
#ifdef __EXCEPTIONS
            throw runtime_error(sout.str());
#else
            gLog << ___err___ << "ERROR - " << sout.str() << endl;
            return false;
#endif
        }

        /// Overload of the ofits method. Just calls the zofits specific one with default, uncompressed options for this column
        bool AddColumn(uint32_t cnt, char typechar, const string& name, const string& unit, const string& comment="", bool addHeaderKeys=true)
        {
            return AddColumn(kFactRaw, cnt, typechar, name, unit, comment, addHeaderKeys);
        }

        /// Overload of the simplified compressed version
        bool AddColumn(const FITS::Compression &comp, uint32_t cnt, char typechar, const string& name, const string& unit, const string& comment="", bool addHeaderKeys=true)
        {
            if (!ofits::AddColumn(1, 'Q', name, unit, comment, addHeaderKeys))
                return false;

            Table::Column col;
            size_t size = SizeFromType(typechar);

            col.name   = name;
            col.type   = typechar;
            col.num    = cnt;
            col.size   = size;
            col.offset = fRealRowWidth;

            fRealRowWidth += size*cnt;

            fRealColumns.emplace_back(CompressedColumn(col, comp));

            ostringstream strKey, strVal, strCom;
            strKey << "ZFORM" << fRealColumns.size();
            strVal << cnt << typechar;
            strCom << "format of " << name << " [" << CommentFromType(typechar);
            SetStr(strKey.str(), strVal.str(), strCom.str());

            strKey.str("");
            strVal.str("");
            strCom.str("");
            strKey << "ZCTYP" << fRealColumns.size();
            strVal << "FACT";
            strCom << "Compression type FACT";
            SetStr(strKey.str(), strVal.str(), strCom.str());

            return true;
        }

        /// static setter for the default number of threads to use. -1 means all available physical cores
        static void SetDefaultNumThreads   (int32_t num)   { fgNumQueues = num;}
        static void SetDefaultNumTiles     (uint32_t num)  { fgNumTiles = num;}
        static void SetDefaultNumRowPerTile(uint32_t num)  { fgRowPerTile = num;}
        static void SetDefaultMaxUsableMem (uint64_t size) { fgMaxUsableMem = size;}

        static int32_t GetDefaultNumThreads()     { return fgNumQueues;}
        static uint32_t GetDefaultNumTiles()      { return fgNumTiles;}
        static uint32_t GetDefaultNumRowPerTile() { return fgRowPerTile;}
        static uint64_t GetDefaulMaxUsableMem()   { return fgMaxUsableMem;}

        /// Get and set the actual number of threads for this object
        int32_t GetNumThreads() const { return fNumQueues;}
        bool SetNumThreads(int32_t num)
        {
            if (is_open())
            {
#ifdef __EXCEPTIONS
                throw runtime_error("File must be closed before changing the number of compression threads");
#else
                gLog << ___err___ << "ERROR - File must be closed before changing the number of compression threads" << endl;
#endif
                return false;
            }

            //get number of physically available threads
#ifdef USE_BOOST_THREADS
            int32_t num_available_cores = boost::thread::hardware_concurrency();
#else
            int32_t num_available_cores = thread::hardware_concurrency();
#endif

            // could not detect number of available cores from system properties...
            // assume that 5 cores are available (4 compression, 1 write)
            if (num_available_cores == 0)
                num_available_cores = 5;

            // Throw an exception if too many cores are requested
            if (num > num_available_cores)
            {
                ostringstream str;
                str << "You will be using more threads(" << num << ") than available cores(" << num_available_cores << "). Expect sub-optimal performances";
#ifdef __EXCEPTIONS
                throw runtime_error(str.str());
#else
                gLog << ___err___ << "WARNING - " << str.str() << endl;
#endif
            }

            if (num == -1)
                num = num_available_cores-2; // 1 for writing, 1 for the main thread

            if (fCompressionQueues.size() == (uint32_t)num)
                return true;

            //cannot be const, as resize does not want it that way
            Queue<CompressionTarget> queue(bind(&zofits::CompressBuffer, this, placeholders::_1), false);

            //shrink if required
            if ((uint32_t)num < fCompressionQueues.size())
            {
                fCompressionQueues.resize(num, queue);
                return true;
            }

            //grow if required
            fCompressionQueues.resize(num, queue);

            fNumQueues = num;

            return true;
        }

protected:

        /// Allocates the required objects.
        void reallocateBuffers()
        {
            const size_t chunk_size = fRealRowWidth*fNumRowsPerTile + fRealColumns.size()*sizeof(BlockHeader) + sizeof(TileHeader) + 8; //+8 for checksuming;
            fMemPool.setChunkSize(chunk_size);

            fSmartBuffer = fMemPool.malloc();
            fBuffer      = fSmartBuffer.get()->get();

            fRawSumBuffer.resize(fRealRowWidth + 4-fRealRowWidth%4); //for checksuming

            //give the catalog enough space
            fCatalog.resize(fNumTiles);
            for (uint32_t i=0;i<fNumTiles;i++)
            {
                fCatalog[i].resize(fRealColumns.size());
                for (auto it=fCatalog[i].begin(); it!=fCatalog[i].end(); it++)
                    *it = CatalogEntry(0,0);
            }
        }

        /// Actually does the writing to disk (and checksuming)
        /// @param src the buffer to write
        /// @param sizeToWrite how many bytes should be written
        /// @return the state of the file
        bool writeCompressedDataToDisk(char* src, const uint32_t sizeToWrite)
        {
            char* checkSumPointer = src+4;
            int32_t extraBytes = 0;
            uint32_t sizeToChecksum = sizeToWrite;
            if (fCheckOffset != 0)
            {//should we extend the array to the left ?
                sizeToChecksum += fCheckOffset;
                checkSumPointer -= fCheckOffset;
                memset(checkSumPointer, 0, fCheckOffset);
            }
            if (sizeToChecksum%4 != 0)
            {//should we extend the array to the right ?
                extraBytes = 4 - (sizeToChecksum%4);
                memset(checkSumPointer+sizeToChecksum, 0,extraBytes);
                sizeToChecksum += extraBytes;
            }

            //do the checksum
            fDataSum.add(checkSumPointer, sizeToChecksum);

            fCheckOffset = (4 - extraBytes)%4;
            //write data to disk
            write(src+4, sizeToWrite);

            return good();
        }

        /// Compress a given buffer based on the target. This is the method executed by the threads
        /// @param target the struct hosting the parameters of the compression
        /// @return number of bytes of the compressed data, or always 1 when used by the Queues
        uint32_t CompressBuffer(const CompressionTarget& target)
        {
            uint64_t compressed_size = 0;
#ifdef __EXCEPTIONS
            try
            {
#endif
                //transpose the original data
                copyTransposeTile(target.src.get()->get(), target.transposed_src.get()->get());

                //compress the buffer
                compressed_size = compressBuffer(target.target.data.get()->get(), target.transposed_src.get()->get(), target.num_rows);
#ifdef __EXCEPTIONS
            }
            catch (...)
            {
                fThreadsException = current_exception();
                if (fNumQueues == 0)
                    rethrow_exception(fThreadsException);
            }
#endif

            if (fNumQueues == 0)
                return compressed_size;

            //post the result to the writing queue
            //get a copy so that it becomes non-const
            WriteTarget wt;
            wt.tile_num = target.target.tile_num;
            wt.size     = compressed_size;
            wt.data   = target.target.data;

            fWriteToDiskQueue.post(wt);

            // if used by the queue, always return true as the elements are not ordered
            return 1;
        }

        /// Write one compressed tile to disk. This is the method executed by the writing thread
        /// @param target the struct hosting the write parameters
        bool WriteBufferToDisk(const WriteTarget& target)
        {
            //is this the tile we're supposed to write ?
            if (target.tile_num != (uint32_t)(fLatestWrittenTile+1))
                return false;

            fLatestWrittenTile++;

#ifdef __EXCEPTIONS
            try
            {
#endif
                if (!writeCompressedDataToDisk(target.data.get()->get(), target.size))
                {//could not write the data to disk
                    ostringstream str;
                    str << "An error occured while writing to disk: ";
                    if (eof())
                        str << "End-Of-File";
                    if (failbit)
                        str << "Logical error on i/o operation";
                    if (badbit)
                        str << "Writing error on i/o operation";
#ifdef __EXCEPTIONS
                    throw runtime_error(str.str());
#else
                    gLog << ___err___ << "ERROR - " << str.str() << endl;
#endif
                }
#ifdef __EXCEPTIONS
            }
            catch(...)
            {
                fThreadsException = current_exception();
                if (fNumQueues == 0)
                    rethrow_exception(fThreadsException);
            }
#endif
            return true;
        }

        /// Compress a given buffer based on its source and destination
        //src cannot be const, as applySMOOTHING is done in place
        /// @param dest the buffer hosting the compressed data
        /// @param src the buffer hosting the transposed data
        /// @param num_rows the number of uncompressed rows in the transposed buffer
        /// @param the number of bytes of the compressed data
        uint64_t compressBuffer(char* dest, char* src, uint32_t num_rows)
        {
            const uint32_t thisRoundNumRows  = (num_rows%fNumRowsPerTile) ? num_rows%fNumRowsPerTile : fNumRowsPerTile;
            const uint32_t currentCatalogRow = (num_rows-1)/fNumRowsPerTile;
            uint32_t       offset            = 0;

            //skip the checksum reserved area
            dest += 4;

            //skip the 'TILE' marker and tile size entry
            uint64_t compressedOffset = sizeof(TileHeader);

            //now compress each column one by one by calling compression on arrays
            for (uint32_t i=0;i<fRealColumns.size();i++)
            {
                fCatalog[currentCatalogRow][i].second = compressedOffset;

                if (fRealColumns[i].col.num == 0) continue;

                Compression& head = fRealColumns[i].block_head;

                //set the default byte telling if uncompressed the compressed Flag
                const uint64_t previousOffset = compressedOffset;

                //skip header data
                compressedOffset += head.getSizeOnDisk();

                for (uint32_t j=0;j<head.getNumProcs();j++)//sequence.size(); j++)
                {
                    switch (head.getProc(j))
                    {
                        case kFactRaw:
                                compressedOffset += compressUNCOMPRESSED(dest + compressedOffset, src  + offset, thisRoundNumRows*fRealColumns[i].col.size*fRealColumns[i].col.num);
                        break;
                        case kFactSmoothing:
                                applySMOOTHING(src + offset, thisRoundNumRows*fRealColumns[i].col.num);
                        break;
                        case kFactHuffman16:
                            if (head.getOrdering() == kOrderByCol)
                                compressedOffset += compressHUFFMAN16(dest + compressedOffset, src  + offset, thisRoundNumRows, fRealColumns[i].col.size, fRealColumns[i].col.num);
                            else
                                compressedOffset += compressHUFFMAN16(dest + compressedOffset, src  + offset, fRealColumns[i].col.num, fRealColumns[i].col.size, thisRoundNumRows);
                        break;
                    }
                }

               //check if compressed size is larger than uncompressed
                if ((head.getProc(0) != kFactRaw) && (compressedOffset - previousOffset > fRealColumns[i].col.size*fRealColumns[i].col.num*thisRoundNumRows+head.getSizeOnDisk()))// && two)
                {//if so set flag and redo it uncompressed
                   // cout << "Redoing uncompressed ! " << endl;
                    //de-smooth !
                    if (head.getProc(0) == kFactSmoothing)
                        UnApplySMOOTHING(src+offset, fRealColumns[i].col.num*thisRoundNumRows);

                    Compression he;

                    compressedOffset = previousOffset + he.getSizeOnDisk();
                    compressedOffset += compressUNCOMPRESSED(dest + compressedOffset, src + offset, thisRoundNumRows*fRealColumns[i].col.size*fRealColumns[i].col.num);

                    he.SetBlockSize(compressedOffset - previousOffset);
                    he.Memcpy(dest+previousOffset);

                    offset += thisRoundNumRows*fRealColumns[i].col.size*fRealColumns[i].col.num;

                    fCatalog[currentCatalogRow][i].first = compressedOffset - fCatalog[currentCatalogRow][i].second;
                    continue;
                }

                head.SetBlockSize(compressedOffset - previousOffset);
                head.Memcpy(dest + previousOffset);

                offset += thisRoundNumRows*fRealColumns[i].col.size*fRealColumns[i].col.num;
                fCatalog[currentCatalogRow][i].first = compressedOffset - fCatalog[currentCatalogRow][i].second;
            }

            TileHeader tile_head(thisRoundNumRows, compressedOffset);
            memcpy(dest, &tile_head, sizeof(TileHeader));

            return compressedOffset;
        }

        /// Transpose a tile to a new buffer
        /// @param src buffer hosting the regular, row-ordered data
        /// @param dest the target buffer that will receive the transposed data
        void copyTransposeTile(const char* src, char* dest)
        {
            const uint32_t thisRoundNumRows = (fTable.num_rows%fNumRowsPerTile) ? fTable.num_rows%fNumRowsPerTile : fNumRowsPerTile;

            //copy the tile and transpose it
            for (uint32_t i=0;i<fRealColumns.size();i++)
            {
                switch (fRealColumns[i].block_head.getOrdering())
                {
                    case kOrderByRow:
                        for (uint32_t k=0;k<thisRoundNumRows;k++)
                        {//regular, "semi-transposed" copy
                            memcpy(dest, src+k*fRealRowWidth+fRealColumns[i].col.offset, fRealColumns[i].col.size*fRealColumns[i].col.num);
                            dest += fRealColumns[i].col.size*fRealColumns[i].col.num;
                        }
                    break;

                    case kOrderByCol :
                        for (uint32_t j=0;j<fRealColumns[i].col.num;j++)
                            for (uint32_t k=0;k<thisRoundNumRows;k++)
                            {//transposed copy
                                memcpy(dest, src+k*fRealRowWidth+fRealColumns[i].col.offset+fRealColumns[i].col.size*j, fRealColumns[i].col.size);
                                dest += fRealColumns[i].col.size;
                            }
                    break;
                };
            }
        }

        /// Specific compression functions
        /// @param dest the target buffer
        /// @param src the source buffer
        /// @param size number of bytes to copy
        /// @return number of bytes written
        uint32_t compressUNCOMPRESSED(char* dest, const char* src, uint32_t size)
        {
            memcpy(dest, src, size);
            return size;
        }

        /// Do huffman encoding
        /// @param dest the buffer that will receive the compressed data
        /// @param src the buffer hosting the transposed data
        /// @param numRows number of rows of data in the transposed buffer
        /// @param sizeOfElems size in bytes of one data elements
        /// @param numRowElems number of elements on each row
        /// @return number of bytes written
        uint32_t compressHUFFMAN16(char* dest, const char* src, uint32_t numRows, uint32_t sizeOfElems, uint32_t numRowElems)
        {
            string huffmanOutput;
            uint32_t previousHuffmanSize = 0;
            if (numRows < 2)
            {//if we have less than 2 elems to compress, Huffman encoder does not work (and has no point). Just return larger size than uncompressed to trigger the raw storage.
                return numRows*sizeOfElems*numRowElems + 1000;
            }
            if (sizeOfElems < 2 )
            {
#ifdef __EXCEPTIONS
                throw runtime_error("HUFMANN16 can only encode columns with 16-bit or longer types");
#else
                gLog << ___err___ << "ERROR - HUFMANN16 can only encode columns with 16-bit or longer types" << endl;
                return 0;
#endif
            }
            uint32_t huffmanOffset = 0;
            for (uint32_t j=0;j<numRowElems;j++)
            {
                Huffman::Encode(huffmanOutput,
                                reinterpret_cast<const uint16_t*>(&src[j*sizeOfElems*numRows]),
                                numRows*(sizeOfElems/2));
                reinterpret_cast<uint32_t*>(&dest[huffmanOffset])[0] = huffmanOutput.size() - previousHuffmanSize;
                huffmanOffset += sizeof(uint32_t);
                previousHuffmanSize = huffmanOutput.size();
            }
            const size_t totalSize = huffmanOutput.size() + huffmanOffset;

            //only copy if not larger than not-compressed size
            if (totalSize < numRows*sizeOfElems*numRowElems)
                memcpy(&dest[huffmanOffset], huffmanOutput.data(), huffmanOutput.size());

            return totalSize;
        }

        /// Applies Thomas' DRS4 smoothing
        /// @param data where to apply it
        /// @param numElems how many elements of type int16_t are stored in the buffer
        /// @return number of bytes modified
        uint32_t applySMOOTHING(char* data, uint32_t numElems)
        {
            int16_t* short_data = reinterpret_cast<int16_t*>(data);
            for (int j=numElems-1;j>1;j--)
                short_data[j] = short_data[j] - (short_data[j-1]+short_data[j-2])/2;

            return numElems*sizeof(int16_t);
        }

        /// Apply the inverse transform of the integer smoothing
        /// @param data where to apply it
        /// @param numElems how many elements of type int16_t are stored in the buffer
        /// @return number of bytes modified
        uint32_t UnApplySMOOTHING(char* data, uint32_t numElems)
        {
            int16_t* short_data = reinterpret_cast<int16_t*>(data);
            //un-do the integer smoothing
            for (uint32_t j=2;j<numElems;j++)
                short_data[j] = short_data[j] + (short_data[j-1]+short_data[j-2])/2;

            return numElems*sizeof(uint16_t);
        }



        //thread related stuff
        MemoryManager   fMemPool;                  ///< Actual memory manager, providing memory for the compression buffers
        static int32_t  fgNumQueues;              ///<  Default number of threads to be used by the objects
        static uint32_t fgNumTiles;              ///< Default number of reserved tiles
        static uint32_t fgRowPerTile;           ///< Default number of rows per tile
        static uint64_t fgMaxUsableMem;        ///< Default usable memory PER OBJECT
        int32_t         fNumQueues;           ///<   Current number of threads that will be used by this object
        uint64_t        fMaxUsableMem;       ///<    Maximum number of bytes that can be allocated by the memory manager
        int32_t         fLatestWrittenTile; ///<     Index of the last tile written to disk (for correct ordering while using several threads)

        vector<Queue<CompressionTarget>>          fCompressionQueues;  ///< Processing queues (=threads)
        Queue<WriteTarget, QueueMin<WriteTarget>> fWriteToDiskQueue;  ///<  Writing queue (=thread)

        // catalog related stuff
        struct CatalogEntry
        {
            CatalogEntry(int64_t f=0, int64_t s=0) : first(f), second(s) {};
            int64_t first;   ///< Size of this column in the tile
            int64_t second; ///< offset of this column in the tile, from the start of the heap area
        } __attribute__((__packed__));

        typedef vector<CatalogEntry> CatalogRow;
        typedef vector<CatalogRow>     CatalogType;
        CatalogType fCatalog;               ///< Catalog for this file
//        uint32_t    fCatalogSize;          ///<  Actual catalog size (.size() is slow on large lists)
        uint32_t    fNumTiles;            ///<   Number of pre-reserved tiles
        uint32_t    fNumRowsPerTile;     ///<    Number of rows per tile
        off_t       fCatalogOffset;     ///<     Offset of the catalog from the beginning of the file
        uint32_t    fCatalogExtraRows; ///<      Number of extra rows written on top of the initial capacity of the file

        // checksum related stuff
        Checksum fCatalogSum;    ///< Checksum of the catalog
        Checksum fRawSum;       ///<  Raw sum (specific to FACT)
        int32_t  fCheckOffset; ///<   offset to the data pointer to calculate the checksum

        // data layout related stuff
        /// Regular columns augmented with compression informations
        struct CompressedColumn
        {
            CompressedColumn(const Table::Column& c, const Compression& h) : col(c),
                block_head(h)
            {}
            Table::Column     col;         ///< the regular column entry
            Compression       block_head; ///< the compression data associated with that column
        };
        vector<CompressedColumn> fRealColumns;     ///< Vector hosting the columns of the file
        uint32_t                 fRealRowWidth;   ///<  Width in bytes of one uncompressed row
        shared_ptr<MemoryChunk>  fSmartBuffer;   ///<   Smart pointer to the buffer where the incoming rows are written
        char*                    fBuffer;       ///<    regular version of fSmartBuffer
        vector<char>             fRawSumBuffer;///<     buffer used for checksuming the incoming data, before compression

#ifdef __EXCEPTIONS
        exception_ptr     fThreadsException; ///< exception pointer to store exceptions coming from the threads
#endif

};

int32_t  zofits::fgNumQueues = 0;
uint32_t zofits::fgNumTiles = 1000;
uint32_t zofits::fgRowPerTile = 100;
uint64_t zofits::fgMaxUsableMem = 1073741824; // one gigabyte

#ifndef __MARS__
}; //namespace std
#endif