Big-Data-HPC-Platform/system/jlib/jio.cpp

/*##############################################################################

    Copyright (C) 2011 HPCC Systems.

    All rights reserved. This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    This program 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 Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
############################################################################## */


#include "platform.h"
#include <algorithm>

#include "jfile.hpp"
#include "jthread.hpp"
#include "jio.ipp"
#include "jlzw.ipp"
#include "jmisc.hpp"
#include <time.h>
#include <limits.h>
#include "jexcept.hpp"
#include "jqueue.tpp"

#ifdef _WIN32
#include <io.h>
#endif

#define DEFAULTBUFFERSIZE 0x10000  // 64K
#define RANDOM_BUFFER_SIZE                  DEFAULTBUFFERSIZE
#define MAX_RANDOM_CACHE_SIZE               0x10000
#define RANDOM_CACHE_DEPTH                  10

#define threshold 1024
#define timelimit 100

#define MINCOMPRESSEDROWSIZE 16
#define MAXCOMPRESSEDROWSIZE 0x4000

static unsigned ioRetryCount=0;
void setIORetryCount(unsigned _ioRetryCount) // non atomic, expected to be called just once at process start up.
{
    ioRetryCount = _ioRetryCount;
    PROGLOG("setIORetryCount set to : %d", ioRetryCount);
}

extern jlib_decl offset_t checked_lseeki64( int handle, offset_t offset, int origin )
{
    offset_t ret=_lseeki64(handle,offset,origin);
    if (ret==(offset_t)-1) 
        throw MakeErrnoException("checked_lseeki64");
    return ret;
}

extern jlib_decl size32_t checked_read(int file, void *buffer, size32_t len)
{
    if (0==len) return 0;
    unsigned attempts = 0;
    size32_t ret = 0;
    unsigned __int64 startCycles = get_cycles_now();
    loop
    {
        ssize_t readNow = _read(file, buffer, len);
        if (readNow == (ssize_t)-1)
        {
            switch (errno)
            {
            case EINTR:
                readNow = 0;
                break;
            default:
                if (attempts < ioRetryCount)
                {
                    attempts++;
                    StringBuffer callStr("read");
                    callStr.append("[errno=").append(errno);
                    unsigned __int64 elapsedMs = cycle_to_nanosec(get_cycles_now() - startCycles)/1000000;
                    callStr.append(", took=").append(elapsedMs);
                    callStr.append(", attempt=").append(attempts).append("](handle=");
                    callStr.append(file).append(", len=").append(len).append(")");
                    PROGLOG("%s", callStr.str());
                    readNow = 0;
                    break;
                }
                throw MakeErrnoException(errno, "checked_read");
            }
        }
        else if (!readNow)
            break;
        ret += readNow;
        if (readNow == len)
            break;
        buffer = ((char *) buffer) + readNow;
        len -= readNow;
    }
    return ret;
}

#ifdef WIN32
static bool atomicsupported = true;
static CriticalSection atomicsection;
#endif

extern jlib_decl size32_t checked_pread(int file, void *buffer, size32_t len, offset_t pos)
{
    if (0==len) return 0;
#ifdef WIN32
    if (atomicsupported)
    {
        HANDLE hFile = (HANDLE)_get_osfhandle(file);
        DWORD rread;
        OVERLAPPED overlapped;
        memset(&overlapped, 0, sizeof(overlapped));
        overlapped.Offset = (DWORD) pos;
        overlapped.OffsetHigh = (DWORD)(pos>>32);
        if (ReadFile(hFile, buffer, len, &rread, &overlapped))
            return rread;
        int err = (int)GetLastError();
        if (err == ERROR_HANDLE_EOF)
            return 0;
        if (err == ERROR_INVALID_PARAMETER) // Win98 etc
            atomicsupported = false;
        else
            throw MakeOsException(GetLastError(), "checked_pread");
    }
    {
        CriticalBlock blk(atomicsection);
        checked_lseeki64(file, pos, FILE_BEGIN);
        return checked_read(file, buffer, len);
    }
#else
    size32_t ret = 0;
    unsigned attempts = 0;
    unsigned __int64 startCycles = get_cycles_now();
    loop
    {
        ssize_t readNow = ::pread(file, buffer, len, pos);
        if (readNow == (ssize_t)-1)
        {
            switch (errno)
            {
            case EINTR:
                readNow = 0;
                break;
            default:
                if (attempts < ioRetryCount)
                {
                    attempts++;
                    StringBuffer callStr("pread");
                    callStr.append("[errno=").append(errno);
                    unsigned __int64 elapsedMs = cycle_to_nanosec(get_cycles_now() - startCycles)/1000000;
                    callStr.append(", took=").append(elapsedMs);
                    callStr.append(", attempt=").append(attempts).append("](handle=");
                    callStr.append(file).append(", pos=").append(pos).append(", len=").append(len).append(")");
                    PROGLOG("%s", callStr.str());
                    readNow = 0;
                    break;
                }
                throw MakeErrnoException(errno,"checked_pread");
            }
        }
        else if (!readNow)
            break;
        ret += readNow;
        if (readNow == len)
            break;
        pos += readNow;
        buffer = ((char *) buffer) + readNow;
        len -= readNow;
    }
    return ret;
#endif
}

extern jlib_decl size32_t checked_write( int handle, const void *buffer, size32_t count )
{
    int ret=_write(handle,buffer,count);
    if ((size32_t)ret != count)
    {
        throw MakeErrnoException((ret==-1)?errno:DISK_FULL_EXCEPTION_CODE, "checked_write");
    }
    return (size32_t)ret;
}

class CReadSeq : public CInterface, public IReadSeq
{
    int fh;
    size32_t size;  
    char *buffer;
    char *ptr;
    size32_t bufSize;
    size32_t bytesInBuffer;
    offset_t startpos;
    offset_t endpos;
    offset_t nextbufpos;
    bool compressed;
    void *prev;
    size32_t maxcompsize;
    bool first;

    inline unsigned remaining()
    {
        return (unsigned)(buffer+bytesInBuffer-ptr);
    }

    size32_t getBytes(void *dst, size32_t _size)
    {
        size32_t left = remaining();
        size32_t read = 0;
        while (_size>left) {
            if (left) {
                memcpy(dst, ptr, left);
                dst = (char *)dst + left;
                _size -= left;
                read += left;
                ptr+=left;
            }
            refill();
            left = bytesInBuffer;
            if (!left)
                return read;
        }
        memcpy(dst, ptr, _size);
        ptr += _size;
        read += _size;
        return read;
    }

    void refill()
    {
        size32_t left = remaining();
        memmove(buffer,ptr,left);
        size32_t rd=bufSize-left;
        if (endpos-nextbufpos<(offset_t)rd)
            rd = (size32_t)(endpos-nextbufpos);
        if (rd) 
            rd = checked_pread(fh, buffer+left, rd, nextbufpos);
        nextbufpos += rd;
        bytesInBuffer = left+rd;
        ptr = buffer;
    }


public:
    IMPLEMENT_IINTERFACE;

    CReadSeq(int _fh, offset_t _offset, unsigned maxrecs, size32_t _size, size32_t _bufsize, bool _compressed)
    {
        assertex(_size);
        fh = _fh; 
        size = _size;
        bufSize = (_bufsize==(unsigned) -1)?DEFAULTBUFFERSIZE:_bufsize;
        bytesInBuffer = 0;
        startpos = _offset;
        nextbufpos = _offset;   
        compressed = ((size<bufSize/2)&&(size>=MINCOMPRESSEDROWSIZE)&&(size<=MAXCOMPRESSEDROWSIZE))?_compressed:false;
        if (compressed) {
            maxcompsize = size+size/3+3; // migger than needed
            buffer = (char *) malloc(bufSize+size);
            prev = buffer+bufSize;
        }
        else
            buffer = (char *) malloc(bufSize);
        ptr = buffer;
        first = true;
        endpos = (maxrecs!=(unsigned)-1)?(_offset+(offset_t)maxrecs*(offset_t)_size):I64C(0x7ffffffffff);

    }

    ~CReadSeq() 
    {
        free(buffer);
    }

    virtual bool get(void *dst)
    {
        if (!compressed) 
            return getBytes(dst, size)==size;
        return (getn(dst,1)==1);
    }

    virtual unsigned getn(void *dst, unsigned n)
    {
        if (!compressed)
            return getBytes(dst, size*n)/size;
        byte *d = (byte *)dst;
        byte *e = d+(size*n);
        byte *p = (byte *)prev;
        unsigned ret = 0;
        while (d!=e) {
            if (first) {
                if (getBytes(d, size)!=size)
                    break;
                first = false;
            }
            else {
                if (remaining()<maxcompsize) 
                    refill();
                if (remaining()==0)
                    break;
                ptr += DiffExpand(ptr,d,p,size);
            }
            p = d;
            d += size;
            ret++;
        }
        if (ret)    // we got at least 1 so copy to prev
            memcpy(prev,e-size,size);
        return ret;
    }

    virtual unsigned getRecordSize() 
    { 
        return size; 
    }
    virtual void reset()
    {
        nextbufpos = startpos;
        ptr = buffer;
        bytesInBuffer = 0;
        first = true;
    }
    virtual void stop() 
    {
        free(buffer);   // no one should access after stop
        buffer = NULL;
    } 
};





IReadSeq *createReadSeq(int fh, offset_t _offset, size32_t size, size32_t bufsize, unsigned maxrecs, bool compressed)
{
    if (!bufsize) {
        IReadSeq *seq=new CUnbufferedReadWriteSeq(fh, _offset, size);
        seq->reset(); // not done itself 
        return seq;
    }
    return new CReadSeq(fh, _offset, maxrecs, size, bufsize, compressed);
}



//================================================================================================


class CWriteSeq : public CInterface, public IWriteSeq
{
private:
    int fh;
    size32_t size;
    char *buffer;
    char *ptr;
    size32_t bufSize;
    offset_t fpos;
    bool compressed;
    size32_t maxcompsize;
    void *prev;
    void *aux;
    bool first;

    inline size32_t remaining() 
    {
        return (size32_t)(bufSize - (ptr-buffer));
    }

    void putBytes(const void *src, size32_t _size)
    {
        fpos += _size;
        size32_t left = remaining();
        if (_size>left)
        {
            if (ptr!=buffer) { // don't buffer if entire block
                memcpy(ptr, src, left);
                ptr += left;
                src = (char *)src + left;
                _size -= left;
                flush();
                left = bufSize;
            }
            while (_size>=bufSize) // write out directly
            {
                checked_write(fh, src, bufSize); // stick to writing bufSize blocks
                src = (char *)src + bufSize;
                _size -= bufSize;
            }
        }
        memcpy(ptr, src, _size);
        ptr += _size;
    }

public:
    IMPLEMENT_IINTERFACE;

    CWriteSeq(int _fh, size32_t _size, size32_t _bufsize, bool _compressed)
    {
        assertex(_fh);
        assertex(_size);
        fh = _fh; 
        size = _size;
        fpos = 0;
        if (_bufsize == (unsigned) -1)
            _bufsize = DEFAULTBUFFERSIZE;
        bufSize = _bufsize;
        
        compressed = ((size<bufSize/2)&&(size>=MINCOMPRESSEDROWSIZE)&&(size<=MAXCOMPRESSEDROWSIZE))?_compressed:false;
        if (compressed) {
            maxcompsize = size+size/3+3; // bigger than needed
            buffer = (char *) malloc(bufSize+size+maxcompsize);
            prev = buffer+bufSize;
            aux = (char *)prev+size;
        }
        else
            buffer = (char *) malloc(bufSize);

        ptr = buffer;
        first = true;
    }

    ~CWriteSeq()
    {
        free(buffer);
    }


    void put(const void *src)
    {
        if (compressed) {
            if (first) {
                first = false;
                memcpy(prev,src,size);
            }
            else if (remaining()>=maxcompsize) {
                size32_t sz = DiffCompress(src,ptr,prev,size);
                fpos += sz;
                ptr += sz;
                return;
            }
            else { 
                putBytes(aux, DiffCompress(src,aux,prev,size));
                return;
            }
        }
        putBytes(src, size);
    }

    void putn(const void *src, unsigned numRecs)
    {
        if (compressed) {
            while (numRecs) {
                put(src);
                src = (byte *)src+size;
                numRecs--;
            }
        }
        else
            putBytes(src, size*numRecs);
    }

    void flush()
    {
        if (ptr != buffer)
        {
            checked_write(fh, buffer, (size32_t)(ptr-buffer));
            ptr = buffer;
        }
    }

    offset_t getPosition()
    {
        return fpos;
    }

    virtual size32_t getRecordSize() 
    { 
        return size; 
    }

};

IWriteSeq *createWriteSeq(int fh, size32_t size, size32_t bufsize, bool compressed)
{
    // Async TBD
    if (!bufsize)
        return new CUnbufferedReadWriteSeq(fh, 0, size);
    else
        return new CWriteSeq(fh, size, bufsize,compressed);
}

IWriteSeq *createTeeWriteSeq(IWriteSeq *f1, IWriteSeq *f2)
{
    return new CTeeWriteSeq(f1, f2);
}

//===========================================================================================

CUnbufferedReadWriteSeq::CUnbufferedReadWriteSeq(int _fh, offset_t _offset, size32_t _size)
{
    fh = _fh;
    size = _size;
    offset = _offset;
    fpos = _offset;

}

void CUnbufferedReadWriteSeq::put(const void *src)
{
    checked_write(fh, src, size);
    fpos += size;
}

void CUnbufferedReadWriteSeq::putn(const void *src, unsigned n)
{
    checked_write(fh, src, size*n);
    fpos += size*n;
}

void CUnbufferedReadWriteSeq::flush()
{}

offset_t CUnbufferedReadWriteSeq::getPosition()
{
    return fpos;
}

bool CUnbufferedReadWriteSeq::get(void *dst)
{
    size32_t toread = size;
    while (toread)
    {
        int read = checked_read(fh, dst, toread);
        if (!read) 
            return false;
        toread -= read;
        dst = (char *) dst + read;
    }
    return true;
}

unsigned CUnbufferedReadWriteSeq::getn(void *dst, unsigned n)
{
    size32_t toread = size*n;
    size32_t totread = 0;
    while (toread)
    {
        int read = checked_read(fh, dst, toread);
        if (!read) 
            break;
        toread -= read;
        totread += read;
        dst = (char *) dst + read;
    }
    return totread/size;
}

void CUnbufferedReadWriteSeq::reset()
{
    checked_lseeki64(fh, offset, SEEK_SET);
    fpos = offset;
}

//===========================================================================================


//===========================================================================================

CTeeWriteSeq::CTeeWriteSeq(IWriteSeq *_f1, IWriteSeq *_f2)
{
    w1 = _f1;
    w1->Link();
    w2 = _f2;
    w2->Link();
    assertex(w1->getRecordSize()==w2->getRecordSize());
}

CTeeWriteSeq::~CTeeWriteSeq()
{
    w1->Release();
    w2->Release();
}

void CTeeWriteSeq::put(const void *src)
{
    w1->put(src);
    w2->put(src);
}

void CTeeWriteSeq::putn(const void *src, unsigned n)
{
    w1->putn(src, n);
    w2->putn(src, n);
}

void CTeeWriteSeq::flush()
{
    w1->flush();
    w2->flush();
}

size32_t CTeeWriteSeq::getRecordSize()
{
    return w1->getRecordSize();
}

offset_t CTeeWriteSeq::getPosition()
{
    return w1->getPosition();
}

//==================================================================================================

class CFixedRecordSize: public CInterface, public IRecordSize
{
protected:
    size32_t recsize;
public:
    IMPLEMENT_IINTERFACE;

    CFixedRecordSize(size32_t _recsize) { recsize=_recsize; }
    virtual size32_t getRecordSize(const void *)
    {
        return recsize;
    }
    size32_t getFixedSize() const
    {
        return recsize;
    }
};

IRecordSize *createFixedRecordSize(size32_t recsize)
{
    return new CFixedRecordSize(recsize);
}


class CDeltaRecordSize: public CInterface, public IRecordSize
{
protected:
    Owned<IRecordSize> recordSize;
    int delta;
public:
    CDeltaRecordSize(IRecordSize * _recordSize, int _delta) { recordSize.set(_recordSize); delta = _delta; }
    IMPLEMENT_IINTERFACE;

    virtual size32_t getRecordSize(const void * data)
    {
        return recordSize->getRecordSize(data) + delta;
    }
    size32_t getFixedSize() const
    {
        return recordSize->getFixedSize()?recordSize->getFixedSize()+delta:0;
    }
};

extern jlib_decl IRecordSize *createDeltaRecordSize(IRecordSize * size, int delta)
{
    if (delta == 0)
        return LINK(size);
    return new CDeltaRecordSize(size, delta);
}

//==================================================================================================

// Elevator scanning
#define MAX_PENDING 20000

class ElevatorScanner;

class PendingFetch : public CInterface, public IInterface
{
public:
    IMPLEMENT_IINTERFACE;

    static int compare(const void *a, const void *b);

    offset_t pos;
    IReceiver *receiver;
    void *target;
    IRecordFetchChannel *channel;
};

class ElevatorChannel : public CInterface, implements IRecordFetchChannel
{
private:
    bool cancelled;
    bool immediate;
    ElevatorScanner &scanner;
public:
    IMPLEMENT_IINTERFACE;

    ElevatorChannel(ElevatorScanner &, bool);
    ~ElevatorChannel();

//Interface IRecordFetchChannel
    virtual void fetch(offset_t pos, void *buffer, IReceiver *receiver);
    virtual void flush();
    virtual void abort() { cancelled = true; }
    virtual bool isAborted() { return cancelled; }
    virtual bool isImmediate() { return immediate; }
};

class ElevatorScanner : public Thread, public IRecordFetcher
{
private:
    Monitor scanlist;
    Monitor isRoom;
    PendingFetch pending[MAX_PENDING];
    unsigned nextSlot;
    size32_t recordSize;
    int file;
    offset_t reads;
    unsigned scans;
    bool stopped;
    unsigned duetime;

    void scan();
    void doFetch(PendingFetch &);
    void stop();
    void resetTimer()
    {
        duetime = msTick()+timelimit;
    }

public:
    IMPLEMENT_IINTERFACE;
    virtual void beforeDispose();
    
    ElevatorScanner(int file, size32_t recordSize);
    ~ElevatorScanner();

//Interface IRecordFetcher
    virtual IRecordFetchChannel *openChannel(bool immediate) { return new ElevatorChannel(*this, immediate); }

//Interface Thread
    virtual int run();

    void flush(IRecordFetchChannel *);
    void fetch(offset_t, void *, IReceiver *, IRecordFetchChannel *);
};
    
int PendingFetch::compare(const void *a, const void *b)
{ 
    offset_t aa = ((PendingFetch *) a)->pos;
    offset_t bb = ((PendingFetch *) b)->pos;
    if (aa > bb)
        return 1;
    else if (aa == bb)
        return 0;
    else
        return -1;
}

ElevatorChannel::ElevatorChannel(ElevatorScanner &_scanner, bool _immediate) : scanner(_scanner)
{
    scanner.Link();
    cancelled = false;
    immediate = _immediate;
}

ElevatorChannel::~ElevatorChannel()
{
    flush();
    scanner.Release();
}

void ElevatorChannel::fetch(offset_t fpos, void *buffer, IReceiver *receiver)
{
    scanner.fetch(fpos, buffer, receiver, this);
}

void ElevatorChannel::flush()
{
    scanner.flush(this);
}

ElevatorScanner::ElevatorScanner(int _file, size32_t _recordSize) : Thread("ElevatorScanner")
{
    file = _file;
    recordSize = _recordSize;
    nextSlot = 0;
    reads = 0;
    scans = 0;
    stopped = false;
    start();
}

ElevatorScanner::~ElevatorScanner()
{
    PrintLog("Elevator scanner statistics: %"I64F"d reads (%"I64F"d bytes), %d scans", reads, reads*recordSize, scans);
}

void ElevatorScanner::beforeDispose()
{
    stop();
    join();
}

void ElevatorScanner::fetch(offset_t fpos, void *buffer, IReceiver *receiver, IRecordFetchChannel *channel)
{
    synchronized procedure(scanlist);
    if (channel->isImmediate())
    {
        // MORE - atomic seek/read would be preferable!
        checked_lseeki64(file, fpos, SEEK_SET);
        checked_read(file, buffer, recordSize);
        reads++;
        if (!receiver->takeRecord(fpos))
            channel->abort();
        return;
    }
    {
        synchronized block(isRoom);
        while (nextSlot >= MAX_PENDING)
            isRoom.wait();
    }
    if (!channel->isAborted())
    {
        pending[nextSlot].pos = fpos;
        pending[nextSlot].receiver = receiver;
        pending[nextSlot].target = buffer;
        pending[nextSlot].channel = channel;
    
        nextSlot++;
        resetTimer();
        scanlist.notify();
    }
}

void ElevatorScanner::doFetch(PendingFetch &next)
{
    if (!next.channel->isAborted())
    {
        // MORE - atomic seek/read would be preferable!
        checked_lseeki64(file, next.pos, SEEK_SET);
        checked_read(file, next.target, recordSize);
        reads++;
        if (!next.receiver->takeRecord(next.pos))
            next.channel->abort();
    }
}

void ElevatorScanner::scan()
{
    PrintLog("Starting elevator scan of %d items", nextSlot);
    scans++;
    qsort(pending, nextSlot, sizeof(pending[0]), PendingFetch::compare);
    for (unsigned i = 0; i < nextSlot; i++)
    {
        doFetch(pending[i]);
    }
    nextSlot = 0;
    {
        synchronized block(isRoom);
        isRoom.notify();
    }
    PrintLog("Finished elevator scan");
}

void ElevatorScanner::flush(IRecordFetchChannel *)
{
    // MORE - I could just flush what was asked for, but I may as well flush the lot.
    synchronized procedure(scanlist);
    if (nextSlot)
        scan();
}

int ElevatorScanner::run()
{
    scanlist.lock();
    for (;;)
    {
        while (nextSlot<MAX_PENDING)
        {
            if (nextSlot)
            {
                //  if (!connections.length())
                //      break;
                int timeleft = (int)(duetime-msTick());             
                if (timeleft<=0)
                    break;
            }

            if (stopped)
            {
                scanlist.unlock();
                return 0;
            }
            // MORE - need a timeout on the wait!
            scanlist.wait();
        }
        scan();
    }
}

void ElevatorScanner::stop()
{
    synchronized procedure(scanlist);
    if (!stopped)
    {
        stopped = true;
        scanlist.notify();
    }
}

extern jlib_decl IRecordFetcher *createElevatorFetcher(int file, size32_t recSize)
{
    return new ElevatorScanner(file, recSize);
}

//==================================================================================================
// chained routines allowing multiple streams to be concatenated
// all streams assumed to have same record size


class CChainedWriteSeq : public CInterface, public IWriteSeq
{
protected:
    IWriteSeq *stream;
    IWriteSeqAllocator *allocator;
    unsigned num;
    size32_t recsize;
    offset_t pos;
public:
    IMPLEMENT_IINTERFACE;
    CChainedWriteSeq(IWriteSeqAllocator *_allocator) 
    {
        allocator = _allocator;
        allocator->Link();
        num = 0;
        recsize = 0;
        pos = 0;
    }
    virtual ~CChainedWriteSeq() 
    {
        ::Release(stream);
        allocator->Release();
    }
    void flush() { if (stream) stream->flush(); }
    void put(const void *dst) { putn(dst,1); }
    void putn(const void *dst, unsigned numrecs)
    {
        if (numrecs==0) return;
        if (stream==NULL) return; // could raise exception instead
        byte *out=(byte *)dst;
        while (numrecs>num) {
            stream->putn(out,num);
            pos+=num;
            numrecs-=num;
            stream->flush();
            IWriteSeq *oldstream=stream;
            stream = allocator->next(num);
            oldstream->Release();
            if (!stream) {
                return; // could raise exception
            }
        }
        stream->putn(out,numrecs);
        pos+=numrecs;
    }
    virtual size32_t getRecordSize() { if ((recsize==0)&&stream) recsize = stream->getRecordSize(); return recsize; }
    virtual offset_t getPosition()   { return pos; }
};


class CChainedReadSeq : public CInterface, public IReadSeq
{
protected:
    IReadSeq *stream;
    IReadSeqAllocator *allocator;
    unsigned num;
    size32_t recsize;
public:
    IMPLEMENT_IINTERFACE;
    CChainedReadSeq(IReadSeqAllocator *_allocator)
    {
        allocator = _allocator;
        allocator->Link();
        stream = allocator->next();
        num = 0;
        recsize = 0;
    }
    virtual ~CChainedReadSeq()
    {
        ::Release(stream);
        allocator->Release();
    }
    virtual bool get(void *dst) { return (getn(dst,1)==1); }
    virtual unsigned getn(void *dst, unsigned n) 
    { 
        unsigned done=0;
        while (stream&&n) {
            unsigned r = stream->getn(dst,n); 
            if (r==0) {
                IReadSeq *oldstream=stream;
                stream = allocator->next();
                oldstream->Release();
            }
            else {
                n-=r;
                done+=r;
            }
        }
        return done;
    }
    virtual size32_t getRecordSize()  { return stream->getRecordSize(); }
    virtual void reset()            { stream->reset(); }
    virtual void stop()             { stream->stop(); }

};



unsigned copySeq(IReadSeq *from,IWriteSeq *to,size32_t bufsize)
{
    size32_t recsize=from->getRecordSize();
    assertex(recsize==to->getRecordSize());
    unsigned nbuf = bufsize/recsize;
    if (nbuf==0)
        nbuf = 1;
    MemoryAttr ma;
    byte *buf=(byte *)ma.allocate(nbuf*recsize);
    unsigned ret = 0;
    loop {
        unsigned n = from->getn(buf,nbuf);
        if (n==0)
            break;
        to->putn(buf,n);
        ret += n;
    }
    return ret;
}

/////////////////

CBufferedIOStreamBase::CBufferedIOStreamBase(size32_t _bufferSize)
{
    bufferSize = _bufferSize;
    numInBuffer = 0;
    curBufferOffset = 0;
    reading = true;
    minDirectSize = std::min(bufferSize/4,(size32_t)0x2000);        // size where we don't bother copying into the buffer
}

size32_t CBufferedIOStreamBase::doread(size32_t len, void * data)
{
    if (!reading)
    {
        doflush();
        reading = true;
    }

    size32_t sizeGot = readFromBuffer(len, data);
    len -= sizeGot;
    if (len!=0) 
    {
        data = (char *)data + sizeGot;
        if (len >= minDirectSize)
            sizeGot += directRead(len, data);   // if direct read specified don't loop
        else 
        {
            do  
            {
                if (!fillBuffer())
                    break;
                size32_t numRead = readFromBuffer(len, data);
                sizeGot += numRead;
                len -= numRead; 
                data = (char *)data + numRead;
            } while (len);
        }
    }
    return sizeGot;
}



size32_t CBufferedIOStreamBase::dowrite(size32_t len, const void * data)
{
    if (reading)
    {
        curBufferOffset = 0;
        numInBuffer = 0;
        reading = false;
    }

    size32_t ret = len;
    while (len) {                       // tries to write in buffer size chunks, also flushes as soon as possible
        size32_t wr;
        if (numInBuffer != 0) {
            wr = std::min(len,bufferSize-curBufferOffset);
            writeToBuffer(wr, data);
            if (numInBuffer==bufferSize)
                doflush();
            len -= wr;
            if (len==0)
                break;
            data = (char *)data + wr;
        }
        if (len >= minDirectSize) 
            return directWrite(len, data)+ret-len;
        wr = std::min(len,bufferSize);
        writeToBuffer(wr, data);
        if (numInBuffer==bufferSize)
            doflush();
        len -= wr;
        data = (char *)data + wr;
    }
    return ret; // there is a bit of an assumption here that flush always works 
}

////////////////////////////

class CBufferedIIOStream : public CBufferedIOStreamBase, implements IIOStream
{
    Linked<IIOStream> io;
public:
    IMPLEMENT_IINTERFACE;

    CBufferedIIOStream(IIOStream *_io, unsigned bufSize) : CBufferedIOStreamBase(bufSize), io(_io)
    {
        buffer = new byte[bufSize];
    }

    ~CBufferedIIOStream()
    {
        try { flush(); }
        catch (IException *)
        {
            delete [] buffer;
            throw;
        }
        delete [] buffer;
    }

    virtual bool fillBuffer()
    {
        reading = true;
        numInBuffer = io->read(bufferSize, buffer);
        curBufferOffset = 0;
        return numInBuffer!=0;
    }
    virtual size32_t directRead(size32_t len, void * data) 
    { 
        return io->read(len, data); 
    }
    virtual size32_t directWrite(size32_t len, const void * data) 
    { 
        return io->write(len,data); 
    }
    virtual void doflush()
    {
        if (!reading && numInBuffer)
        {
            //Copy numInBuffer out before flush so that destructor doesn't attempt to flush again.
            size32_t numToWrite = numInBuffer;
            numInBuffer = 0;
            io->write(numToWrite, buffer);
            curBufferOffset = 0;
        }
    }

// IIOStream impl.
    virtual size32_t read(size32_t len, void * data) { return CBufferedIOStreamBase::doread(len, data); }
    virtual size32_t write(size32_t len, const void * data) { return CBufferedIOStreamBase::dowrite(len, data); }
    virtual void flush() { doflush(); }
};

IIOStream *createBufferedIOStream(IIOStream *io, unsigned bufSize)
{
    if (bufSize == (unsigned)-1)
        bufSize = DEFAULT_BUFFER_SIZE;
    return new CBufferedIIOStream(io, bufSize);
}


IRowStream *createNullRowStream()
{
    class cNullStream: public CInterface, implements IRowStream
    {
        const void *nextRow() { return NULL; }
        void stop() {}
    public:
        IMPLEMENT_IINTERFACE;
        cNullStream() {}
    };
    return new cNullStream;
}



unsigned copyRowStream(IRowStream *in, IRowWriter *out)
{
    unsigned ret=0;
    loop {
        const void *row = in->nextRow();
        if (!row)
            break;
        ret ++;
        out->putRow(row);
    }
    return ret;
}
unsigned groupedCopyRowStream(IRowStream *in, IRowWriter *out)
{
    unsigned ret=0;
    loop {
        const void *row = in->nextRow();
        if (!row) {
            row = in->nextRow();
            if (!row)
                break;
            out->putRow(NULL);
        }
        ret ++;
        out->putRow(row);
    }
    return ret;
}
unsigned ungroupedCopyRowStream(IRowStream *in, IRowWriter *out)
{
    unsigned ret=0;
    loop {
        const void *row = in->ungroupedNextRow();
        if (!row)
            break;
        ret ++;
        out->putRow(row);
    }
    return ret;
}

class CConcatRowStream : public CInterface, public IRowStream
{
    IArrayOf<IRowStream> oinstreams;
public:
    unsigned num;
    unsigned idx;
    IRowStream **in;
    bool grouped;
    bool needeog;
public:
    IMPLEMENT_IINTERFACE;
    CConcatRowStream(unsigned _num, IRowStream **_in,bool _grouped)
    {
        // in streams assumed valid throughout (i.e. not linked)
        num = _num;
        idx = 0;
        assertex(num);
        oinstreams.ensure(num);
        for (unsigned n = 0;n<num;n++)
            oinstreams.append(*LINK(_in[n]));
        in = oinstreams.getArray();
        grouped = _grouped;
        needeog = false;
    }

    const void *nextRow()
    {
        while (idx<num) {
            const void *row;
            if (grouped) {
                row = in[idx]->nextRow();
                if (row) {
                    needeog = true;
                    return row;
                }
                if (needeog) {
                    needeog = false;
                    return NULL;
                }
            }
            else {
                row = in[idx]->ungroupedNextRow();
                if (row)
                    return row;
            }
            idx++;
        }
        return NULL;
    }
            
    virtual void stop()  
    { 
        while (idx<num)
            in[idx++]->stop(); 
    }

            
};

extern jlib_decl IWriteSeq *createChainedWriteSeq(IWriteSeqAllocator *iwsa)
{
    return new CChainedWriteSeq(iwsa);
}

extern jlib_decl IReadSeq *createChainedReadSeq(IReadSeqAllocator *irsa)
{
    return new CChainedReadSeq(irsa);
}



IRowStream *createConcatRowStream(unsigned numstreams,IRowStream** streams,bool grouped)
{
    return new CConcatRowStream(numstreams,streams,grouped);
}


#ifdef  __x86_64__
void writeStringToStream(IIOStream &out, const char *s) { out.write((size32_t)strlen(s), s); }
void writeCharsNToStream(IIOStream &out, char c, unsigned cnt) { while(cnt--) out.write(1, &c); }
void writeCharToStream(IIOStream &out, char c) { out.write(1, &c); }
#endif