Introduce threadskv8.c for atomic-consistent inserts/deletes for a set of keys in...

[btree] / threadskv8.c

// btree version threadskv8 sched_yield version
//      with reworked bt_deletekey code,
//      phase-fair reader writer lock,
//      librarian page split code,
//      duplicate key management
//      traditional buffer pool manager
//      and ACID batched key updates

// 21 SEP 2014

// author: karl malbrain, malbrain@cal.berkeley.edu

/*
This work, including the source code, documentation
and related data, is placed into the public domain.

The orginal author is Karl Malbrain.

THIS SOFTWARE IS PROVIDED AS-IS WITHOUT WARRANTY
OF ANY KIND, NOT EVEN THE IMPLIED WARRANTY OF
MERCHANTABILITY. THE AUTHOR OF THIS SOFTWARE,
ASSUMES _NO_ RESPONSIBILITY FOR ANY CONSEQUENCE
RESULTING FROM THE USE, MODIFICATION, OR
REDISTRIBUTION OF THIS SOFTWARE.
*/

// Please see the project home page for documentation
// code.google.com/p/high-concurrency-btree

#define _FILE_OFFSET_BITS 64
#define _LARGEFILE64_SOURCE

#ifdef linux
#define _GNU_SOURCE
#endif

#ifdef unix
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <errno.h>
#include <pthread.h>
#else
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <fcntl.h>
#include <process.h>
#include <intrin.h>
#endif

#include <memory.h>
#include <string.h>
#include <stddef.h>

typedef unsigned long long      uid;

#ifndef unix
typedef unsigned long long      off64_t;
typedef unsigned short          ushort;
typedef unsigned int            uint;
#endif

#define BT_ro 0x6f72    // ro
#define BT_rw 0x7772    // rw

#define BT_maxbits              24                                      // maximum page size in bits
#define BT_minbits              9                                       // minimum page size in bits
#define BT_minpage              (1 << BT_minbits)       // minimum page size
#define BT_maxpage              (1 << BT_maxbits)       // maximum page size

//  BTree page number constants
#define ALLOC_page              0       // allocation page
#define ROOT_page               1       // root of the btree
#define LEAF_page               2       // first page of leaves

//      Number of levels to create in a new BTree

#define MIN_lvl                 2

/*
There are six lock types for each node in four independent sets: 
1. (set 1) AccessIntent: Sharable. Going to Read the node. Incompatible with NodeDelete. 
2. (set 1) NodeDelete: Exclusive. About to release the node. Incompatible with AccessIntent. 
3. (set 2) ReadLock: Sharable. Read the node. Incompatible with WriteLock. 
4. (set 2) WriteLock: Exclusive. Modify the node. Incompatible with ReadLock and other WriteLocks. 
5. (set 3) ParentModification: Exclusive. Change the node's parent keys. Incompatible with another ParentModification. 
6. (set 4) AtomicModification: Exclusive. Atomic Update including node is underway. Incompatible with another AtomicModification. 
*/

typedef enum{
        BtLockAccess = 1,
        BtLockDelete = 2,
        BtLockRead   = 4,
        BtLockWrite  = 8,
        BtLockParent = 16,
        BtLockAtomic = 32
} BtLock;

//      definition for phase-fair reader/writer lock implementation

typedef struct {
        ushort rin[1];
        ushort rout[1];
        ushort ticket[1];
        ushort serving[1];
} RWLock;

#define PHID 0x1
#define PRES 0x2
#define MASK 0x3
#define RINC 0x4

//      definition for spin latch implementation

// exclusive is set for write access
// share is count of read accessors
// grant write lock when share == 0

volatile typedef struct {
        ushort exclusive:1;
        ushort pending:1;
        ushort share:14;
} BtSpinLatch;

#define XCL 1
#define PEND 2
#define BOTH 3
#define SHARE 4

//  hash table entries

typedef struct {
        volatile uint slot;             // Latch table entry at head of chain
        BtSpinLatch latch[1];
} BtHashEntry;

//      latch manager table structure

typedef struct {
        uid page_no;                    // latch set page number
        RWLock readwr[1];               // read/write page lock
        RWLock access[1];               // Access Intent/Page delete
        RWLock parent[1];               // Posting of fence key in parent
        RWLock atomic[1];               // Atomic update in progress
        uint split;                             // right split page atomic insert
        uint entry;                             // entry slot in latch table
        uint next;                              // next entry in hash table chain
        uint prev;                              // prev entry in hash table chain
        volatile ushort pin;    // number of outstanding threads
        ushort dirty:1;                 // page in cache is dirty
#ifdef unix
        pthread_t atomictid;    // pid holding atomic lock
#else
        uint atomictid;                 // pid holding atomic lock
#endif
} BtLatchSet;

//      Define the length of the page record numbers

#define BtId 6

//      Page key slot definition.

//      Keys are marked dead, but remain on the page until
//      it cleanup is called. The fence key (highest key) for
//      a leaf page is always present, even after cleanup.

//      Slot types

//      In addition to the Unique keys that occupy slots
//      there are Librarian and Duplicate key
//      slots occupying the key slot array.

//      The Librarian slots are dead keys that
//      serve as filler, available to add new Unique
//      or Dup slots that are inserted into the B-tree.

//      The Duplicate slots have had their key bytes extended
//      by 6 bytes to contain a binary duplicate key uniqueifier.

typedef enum {
        Unique,
        Librarian,
        Duplicate,
        Delete
} BtSlotType;

typedef struct {
        uint off:BT_maxbits;    // page offset for key start
        uint type:3;                    // type of slot
        uint dead:1;                    // set for deleted slot
} BtSlot;

//      The key structure occupies space at the upper end of
//      each page.  It's a length byte followed by the key
//      bytes.

typedef struct {
        unsigned char len;              // this can be changed to a ushort or uint
        unsigned char key[0];
} BtKey;

//      the value structure also occupies space at the upper
//      end of the page. Each key is immediately followed by a value.

typedef struct {
        unsigned char len;              // this can be changed to a ushort or uint
        unsigned char value[0];
} BtVal;

#define BT_maxkey       255             // maximum number of bytes in a key
#define BT_keyarray (BT_maxkey + sizeof(BtKey))

//      The first part of an index page.
//      It is immediately followed
//      by the BtSlot array of keys.

//      note that this structure size
//      must be a multiple of 8 bytes
//      in order to place dups correctly.

typedef struct BtPage_ {
        uint cnt;                                       // count of keys in page
        uint act;                                       // count of active keys
        uint min;                                       // next key offset
        uint garbage;                           // page garbage in bytes
        unsigned char bits:7;           // page size in bits
        unsigned char free:1;           // page is on free chain
        unsigned char lvl:7;            // level of page
        unsigned char kill:1;           // page is being deleted
        unsigned char right[BtId];      // page number to right
} *BtPage;

//  The loadpage interface object

typedef struct {
        BtPage page;            // current page pointer
        BtLatchSet *latch;      // current page latch set
} BtPageSet;

//      structure for latch manager on ALLOC_page

typedef struct {
        struct BtPage_ alloc[1];        // next page_no in right ptr
        unsigned long long dups[1];     // global duplicate key uniqueifier
        unsigned char chain[BtId];      // head of free page_nos chain
} BtPageZero;

//      The object structure for Btree access

typedef struct {
        uint page_size;                         // page size    
        uint page_bits;                         // page size in bits    
#ifdef unix
        int idx;
#else
        HANDLE idx;
#endif
        BtPageZero *pagezero;           // mapped allocation page
        BtSpinLatch lock[1];            // allocation area lite latch
        uint latchdeployed;                     // highest number of latch entries deployed
        uint nlatchpage;                        // number of latch pages at BT_latch
        uint latchtotal;                        // number of page latch entries
        uint latchhash;                         // number of latch hash table slots
        uint latchvictim;                       // next latch entry to examine
        BtHashEntry *hashtable;         // the buffer pool hash table entries
        BtLatchSet *latchsets;          // mapped latch set from buffer pool
        unsigned char *pagepool;        // mapped to the buffer pool pages
#ifndef unix
        HANDLE halloc;                          // allocation handle
        HANDLE hpool;                           // buffer pool handle
#endif
} BtMgr;

typedef struct {
        BtMgr *mgr;                             // buffer manager for thread
        BtPage cursor;                  // cached frame for start/next (never mapped)
        BtPage frame;                   // spare frame for the page split (never mapped)
        uid cursor_page;                                // current cursor page number   
        unsigned char *mem;                             // frame, cursor, page memory buffer
        unsigned char key[BT_keyarray]; // last found complete key
        int found;                              // last delete or insert was found
        int err;                                // last error
        int reads, writes;              // number of reads and writes from the btree
} BtDb;

typedef enum {
        BTERR_ok = 0,
        BTERR_struct,
        BTERR_ovflw,
        BTERR_lock,
        BTERR_map,
        BTERR_read,
        BTERR_wrt,
        BTERR_atomic
} BTERR;

#define CLOCK_bit 0x8000

// B-Tree functions
extern void bt_close (BtDb *bt);
extern BtDb *bt_open (BtMgr *mgr);
extern BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint len, uint lvl, void *value, uint vallen, uint update);
extern BTERR  bt_deletekey (BtDb *bt, unsigned char *key, uint len, uint lvl);
extern int bt_findkey    (BtDb *bt, unsigned char *key, uint keylen, unsigned char *value, uint valmax);
extern BtKey *bt_foundkey (BtDb *bt);
extern uint bt_startkey  (BtDb *bt, unsigned char *key, uint len);
extern uint bt_nextkey   (BtDb *bt, uint slot);

//      manager functions
extern BtMgr *bt_mgr (char *name, uint bits, uint poolsize);
void bt_mgrclose (BtMgr *mgr);

//  Helper functions to return slot values
//      from the cursor page.

extern BtKey *bt_key (BtDb *bt, uint slot);
extern BtVal *bt_val (BtDb *bt, uint slot);

//  The page is allocated from low and hi ends.
//  The key slots are allocated from the bottom,
//      while the text and value of the key
//  are allocated from the top.  When the two
//  areas meet, the page is split into two.

//  A key consists of a length byte, two bytes of
//  index number (0 - 65535), and up to 253 bytes
//  of key value.

//  Associated with each key is a value byte string
//      containing any value desired.

//  The b-tree root is always located at page 1.
//      The first leaf page of level zero is always
//      located on page 2.

//      The b-tree pages are linked with next
//      pointers to facilitate enumerators,
//      and provide for concurrency.

//      When to root page fills, it is split in two and
//      the tree height is raised by a new root at page
//      one with two keys.

//      Deleted keys are marked with a dead bit until
//      page cleanup. The fence key for a leaf node is
//      always present

//  To achieve maximum concurrency one page is locked at a time
//  as the tree is traversed to find leaf key in question. The right
//  page numbers are used in cases where the page is being split,
//      or consolidated.

//  Page 0 is dedicated to lock for new page extensions,
//      and chains empty pages together for reuse. It also
//      contains the latch manager hash table.

//      The ParentModification lock on a node is obtained to serialize posting
//      or changing the fence key for a node.

//      Empty pages are chained together through the ALLOC page and reused.

//      Access macros to address slot and key values from the page
//      Page slots use 1 based indexing.

#define slotptr(page, slot) (((BtSlot *)(page+1)) + (slot-1))
#define keyptr(page, slot) ((BtKey*)((unsigned char*)(page) + slotptr(page, slot)->off))
#define valptr(page, slot) ((BtVal*)(keyptr(page,slot)->key + keyptr(page,slot)->len))

void bt_putid(unsigned char *dest, uid id)
{
int i = BtId;

        while( i-- )
                dest[i] = (unsigned char)id, id >>= 8;
}

uid bt_getid(unsigned char *src)
{
uid id = 0;
int i;

        for( i = 0; i < BtId; i++ )
                id <<= 8, id |= *src++; 

        return id;
}

uid bt_newdup (BtDb *bt)
{
#ifdef unix
        return __sync_fetch_and_add (bt->mgr->pagezero->dups, 1) + 1;
#else
        return _InterlockedIncrement64(bt->mgr->pagezero->dups, 1);
#endif
}

//      Phase-Fair reader/writer lock implementation

void WriteLock (RWLock *lock)
{
ushort w, r, tix;

#ifdef unix
        tix = __sync_fetch_and_add (lock->ticket, 1);
#else
        tix = _InterlockedExchangeAdd16 (lock->ticket, 1);
#endif
        // wait for our ticket to come up

        while( tix != lock->serving[0] )
#ifdef unix
                sched_yield();
#else
                SwitchToThread ();
#endif

        w = PRES | (tix & PHID);
#ifdef  unix
        r = __sync_fetch_and_add (lock->rin, w);
#else
        r = _InterlockedExchangeAdd16 (lock->rin, w);
#endif
        while( r != *lock->rout )
#ifdef unix
                sched_yield();
#else
                SwitchToThread();
#endif
}

void WriteRelease (RWLock *lock)
{
#ifdef unix
        __sync_fetch_and_and (lock->rin, ~MASK);
#else
        _InterlockedAnd16 (lock->rin, ~MASK);
#endif
        lock->serving[0]++;
}

void ReadLock (RWLock *lock)
{
ushort w;
#ifdef unix
        w = __sync_fetch_and_add (lock->rin, RINC) & MASK;
#else
        w = _InterlockedExchangeAdd16 (lock->rin, RINC) & MASK;
#endif
        if( w )
          while( w == (*lock->rin & MASK) )
#ifdef unix
                sched_yield ();
#else
                SwitchToThread ();
#endif
}

void ReadRelease (RWLock *lock)
{
#ifdef unix
        __sync_fetch_and_add (lock->rout, RINC);
#else
        _InterlockedExchangeAdd16 (lock->rout, RINC);
#endif
}

//      Spin Latch Manager

//      wait until write lock mode is clear
//      and add 1 to the share count

void bt_spinreadlock(BtSpinLatch *latch)
{
ushort prev;

  do {
#ifdef unix
        prev = __sync_fetch_and_add ((ushort *)latch, SHARE);
#else
        prev = _InterlockedExchangeAdd16((ushort *)latch, SHARE);
#endif
        //  see if exclusive request is granted or pending

        if( !(prev & BOTH) )
                return;
#ifdef unix
        prev = __sync_fetch_and_add ((ushort *)latch, -SHARE);
#else
        prev = _InterlockedExchangeAdd16((ushort *)latch, -SHARE);
#endif
#ifdef  unix
  } while( sched_yield(), 1 );
#else
  } while( SwitchToThread(), 1 );
#endif
}

//      wait for other read and write latches to relinquish

void bt_spinwritelock(BtSpinLatch *latch)
{
ushort prev;

  do {
#ifdef  unix
        prev = __sync_fetch_and_or((ushort *)latch, PEND | XCL);
#else
        prev = _InterlockedOr16((ushort *)latch, PEND | XCL);
#endif
        if( !(prev & XCL) )
          if( !(prev & ~BOTH) )
                return;
          else
#ifdef unix
                __sync_fetch_and_and ((ushort *)latch, ~XCL);
#else
                _InterlockedAnd16((ushort *)latch, ~XCL);
#endif
#ifdef  unix
  } while( sched_yield(), 1 );
#else
  } while( SwitchToThread(), 1 );
#endif
}

//      try to obtain write lock

//      return 1 if obtained,
//              0 otherwise

int bt_spinwritetry(BtSpinLatch *latch)
{
ushort prev;

#ifdef  unix
        prev = __sync_fetch_and_or((ushort *)latch, XCL);
#else
        prev = _InterlockedOr16((ushort *)latch, XCL);
#endif
        //      take write access if all bits are clear

        if( !(prev & XCL) )
          if( !(prev & ~BOTH) )
                return 1;
          else
#ifdef unix
                __sync_fetch_and_and ((ushort *)latch, ~XCL);
#else
                _InterlockedAnd16((ushort *)latch, ~XCL);
#endif
        return 0;
}

//      clear write mode

void bt_spinreleasewrite(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_and((ushort *)latch, ~BOTH);
#else
        _InterlockedAnd16((ushort *)latch, ~BOTH);
#endif
}

//      decrement reader count

void bt_spinreleaseread(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_add((ushort *)latch, -SHARE);
#else
        _InterlockedExchangeAdd16((ushort *)latch, -SHARE);
#endif
}

//      read page from permanent location in Btree file

BTERR bt_readpage (BtMgr *mgr, BtPage page, uid page_no)
{
off64_t off = page_no << mgr->page_bits;

#ifdef unix
        if( pread (mgr->idx, page, mgr->page_size, page_no << mgr->page_bits) < mgr->page_size ) {
                fprintf (stderr, "Unable to read page %.8x errno = %d\n", page_no, errno);
                return BTERR_read;
        }
#else
OVERLAPPED ovl[1];
uint amt[1];

        memset (ovl, 0, sizeof(OVERLAPPED));
        ovl->Offset = off;
        ovl->OffsetHigh = off >> 32;

        if( !ReadFile(mgr->idx, page, mgr->page_size, amt, ovl)) {
                fprintf (stderr, "Unable to read page %.8x GetLastError = %d\n", page_no, GetLastError());
                return BTERR_read;
        }
        if( *amt <  mgr->page_size ) {
                fprintf (stderr, "Unable to read page %.8x GetLastError = %d\n", page_no, GetLastError());
                return BTERR_read;
        }
#endif
        return 0;
}

//      write page to permanent location in Btree file
//      clear the dirty bit

BTERR bt_writepage (BtMgr *mgr, BtPage page, uid page_no)
{
off64_t off = page_no << mgr->page_bits;

#ifdef unix
        if( pwrite(mgr->idx, page, mgr->page_size, off) < mgr->page_size )
                return BTERR_wrt;
#else
OVERLAPPED ovl[1];
uint amt[1];

        memset (ovl, 0, sizeof(OVERLAPPED));
        ovl->Offset = off;
        ovl->OffsetHigh = off >> 32;

        if( !WriteFile(mgr->idx, page, mgr->page_size, amt, ovl) )
                return BTERR_wrt;

        if( *amt <  mgr->page_size )
                return BTERR_wrt;
#endif
        return 0;
}

//      link latch table entry into head of latch hash table

BTERR bt_latchlink (BtDb *bt, uint hashidx, uint slot, uid page_no, uint loadit)
{
BtPage page = (BtPage)(((uid)slot << bt->mgr->page_bits) + bt->mgr->pagepool);
BtLatchSet *latch = bt->mgr->latchsets + slot;

        if( latch->next = bt->mgr->hashtable[hashidx].slot )
                bt->mgr->latchsets[latch->next].prev = slot;

        bt->mgr->hashtable[hashidx].slot = slot;
        memset (&latch->atomictid, 0, sizeof(latch->atomictid));
        latch->page_no = page_no;
        latch->entry = slot;
        latch->prev = 0;
        latch->pin = 1;

        if( loadit )
          if( bt->err = bt_readpage (bt->mgr, page, page_no) )
                return bt->err;
          else
                bt->reads++;

        return bt->err = 0;
}

//      set CLOCK bit in latch
//      decrement pin count

void bt_unpinlatch (BtLatchSet *latch)
{
#ifdef unix
        if( ~latch->pin & CLOCK_bit )
                __sync_fetch_and_or(&latch->pin, CLOCK_bit);
        __sync_fetch_and_add(&latch->pin, -1);
#else
        if( ~latch->pin & CLOCK_bit )
                _InterlockedOr16 (&latch->pin, CLOCK_bit);
        _InterlockedDecrement16 (&latch->pin);
#endif
}

//  return the btree cached page address

BtPage bt_mappage (BtDb *bt, BtLatchSet *latch)
{
BtPage page = (BtPage)(((uid)latch->entry << bt->mgr->page_bits) + bt->mgr->pagepool);

        return page;
}

//      find existing latchset or inspire new one
//      return with latchset pinned

BtLatchSet *bt_pinlatch (BtDb *bt, uid page_no, uint loadit)
{
uint hashidx = page_no % bt->mgr->latchhash;
BtLatchSet *latch;
uint slot, idx;
uint lvl, cnt;
off64_t off;
uint amt[1];
BtPage page;

  //  try to find our entry

  bt_spinwritelock(bt->mgr->hashtable[hashidx].latch);

  if( slot = bt->mgr->hashtable[hashidx].slot ) do
  {
        latch = bt->mgr->latchsets + slot;
        if( page_no == latch->page_no )
                break;
  } while( slot = latch->next );

  //  found our entry
  //  increment clock

  if( slot ) {
        latch = bt->mgr->latchsets + slot;
#ifdef unix
        __sync_fetch_and_add(&latch->pin, 1);
#else
        _InterlockedIncrement16 (&latch->pin);
#endif
        bt_spinreleasewrite(bt->mgr->hashtable[hashidx].latch);
        return latch;
  }

        //  see if there are any unused pool entries
#ifdef unix
        slot = __sync_fetch_and_add (&bt->mgr->latchdeployed, 1) + 1;
#else
        slot = _InterlockedIncrement (&bt->mgr->latchdeployed);
#endif

        if( slot < bt->mgr->latchtotal ) {
                latch = bt->mgr->latchsets + slot;
                if( bt_latchlink (bt, hashidx, slot, page_no, loadit) )
                        return NULL;
                bt_spinreleasewrite (bt->mgr->hashtable[hashidx].latch);
                return latch;
        }

#ifdef unix
        __sync_fetch_and_add (&bt->mgr->latchdeployed, -1);
#else
        _InterlockedDecrement (&bt->mgr->latchdeployed);
#endif
  //  find and reuse previous entry on victim

  while( 1 ) {
#ifdef unix
        slot = __sync_fetch_and_add(&bt->mgr->latchvictim, 1);
#else
        slot = _InterlockedIncrement (&bt->mgr->latchvictim) - 1;
#endif
        // try to get write lock on hash chain
        //      skip entry if not obtained
        //      or has outstanding pins

        slot %= bt->mgr->latchtotal;

        if( !slot )
                continue;

        latch = bt->mgr->latchsets + slot;
        idx = latch->page_no % bt->mgr->latchhash;

        //      see we are on same chain as hashidx

        if( idx == hashidx )
                continue;

        if( !bt_spinwritetry (bt->mgr->hashtable[idx].latch) )
                continue;

        //  skip this slot if it is pinned
        //      or the CLOCK bit is set

        if( latch->pin ) {
          if( latch->pin & CLOCK_bit ) {
#ifdef unix
                __sync_fetch_and_and(&latch->pin, ~CLOCK_bit);
#else
                _InterlockedAnd16 (&latch->pin, ~CLOCK_bit);
#endif
          }
          bt_spinreleasewrite (bt->mgr->hashtable[idx].latch);
          continue;
        }

        //  update permanent page area in btree from buffer pool

        page = (BtPage)(((uid)slot << bt->mgr->page_bits) + bt->mgr->pagepool);

        if( latch->dirty )
          if( bt->err = bt_writepage (bt->mgr, page, latch->page_no) )
                return NULL;
          else
                latch->dirty = 0, bt->writes++;

        //  unlink our available slot from its hash chain

        if( latch->prev )
                bt->mgr->latchsets[latch->prev].next = latch->next;
        else
                bt->mgr->hashtable[idx].slot = latch->next;

        if( latch->next )
                bt->mgr->latchsets[latch->next].prev = latch->prev;

        bt_spinreleasewrite (bt->mgr->hashtable[idx].latch);

        if( bt_latchlink (bt, hashidx, slot, page_no, loadit) )
                return NULL;

        bt_spinreleasewrite (bt->mgr->hashtable[hashidx].latch);
        return latch;
  }
}

void bt_mgrclose (BtMgr *mgr)
{
BtLatchSet *latch;
uint num = 0;
BtPage page;
uint slot;

        //      flush dirty pool pages to the btree

        for( slot = 1; slot <= mgr->latchdeployed; slot++ ) {
                page = (BtPage)(((uid)slot << mgr->page_bits) + mgr->pagepool);
                latch = mgr->latchsets + slot;

                if( latch->dirty ) {
                        bt_writepage(mgr, page, latch->page_no);
                        latch->dirty = 0, num++;
                }
//              madvise (page, mgr->page_size, MADV_DONTNEED);
        }

        fprintf(stderr, "%d buffer pool pages flushed\n", num);

#ifdef unix
        munmap (mgr->hashtable, (uid)mgr->nlatchpage << mgr->page_bits);
        munmap (mgr->pagezero, mgr->page_size);
#else
        FlushViewOfFile(mgr->pagezero, 0);
        UnmapViewOfFile(mgr->pagezero);
        UnmapViewOfFile(mgr->hashtable);
        CloseHandle(mgr->halloc);
        CloseHandle(mgr->hpool);
#endif
#ifdef unix
        close (mgr->idx);
        free (mgr);
#else
        FlushFileBuffers(mgr->idx);
        CloseHandle(mgr->idx);
        GlobalFree (mgr);
#endif
}

//      close and release memory

void bt_close (BtDb *bt)
{
#ifdef unix
        if( bt->mem )
                free (bt->mem);
#else
        if( bt->mem)
                VirtualFree (bt->mem, 0, MEM_RELEASE);
#endif
        free (bt);
}

//  open/create new btree buffer manager

//      call with file_name, BT_openmode, bits in page size (e.g. 16),
//              size of page pool (e.g. 262144)

BtMgr *bt_mgr (char *name, uint bits, uint nodemax)
{
uint lvl, attr, last, slot, idx;
uint nlatchpage, latchhash;
unsigned char value[BtId];
int flag, initit = 0;
BtPageZero *pagezero;
off64_t size;
uint amt[1];
BtMgr* mgr;
BtKey* key;
BtVal *val;

        // determine sanity of page size and buffer pool

        if( bits > BT_maxbits )
                bits = BT_maxbits;
        else if( bits < BT_minbits )
                bits = BT_minbits;

        if( nodemax < 16 ) {
                fprintf(stderr, "Buffer pool too small: %d\n", nodemax);
                return NULL;
        }

#ifdef unix
        mgr = calloc (1, sizeof(BtMgr));

        mgr->idx = open ((char*)name, O_RDWR | O_CREAT, 0666);

        if( mgr->idx == -1 ) {
                fprintf (stderr, "Unable to open btree file\n");
                return free(mgr), NULL;
        }
#else
        mgr = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, sizeof(BtMgr));
        attr = FILE_ATTRIBUTE_NORMAL;
        mgr->idx = CreateFile(name, GENERIC_READ| GENERIC_WRITE, FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, attr, NULL);

        if( mgr->idx == INVALID_HANDLE_VALUE )
                return GlobalFree(mgr), NULL;
#endif

#ifdef unix
        pagezero = valloc (BT_maxpage);
        *amt = 0;

        // read minimum page size to get root info
        //      to support raw disk partition files
        //      check if bits == 0 on the disk.

        if( size = lseek (mgr->idx, 0L, 2) )
                if( pread(mgr->idx, pagezero, BT_minpage, 0) == BT_minpage )
                        if( pagezero->alloc->bits )
                                bits = pagezero->alloc->bits;
                        else
                                initit = 1;
                else
                        return free(mgr), free(pagezero), NULL;
        else
                initit = 1;
#else
        pagezero = VirtualAlloc(NULL, BT_maxpage, MEM_COMMIT, PAGE_READWRITE);
        size = GetFileSize(mgr->idx, amt);

        if( size || *amt ) {
                if( !ReadFile(mgr->idx, (char *)pagezero, BT_minpage, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;
                bits = pagezero->alloc->bits;
        } else
                initit = 1;
#endif

        mgr->page_size = 1 << bits;
        mgr->page_bits = bits;

        //  calculate number of latch hash table entries

        mgr->nlatchpage = (nodemax/16 * sizeof(BtHashEntry) + mgr->page_size - 1) / mgr->page_size;
        mgr->latchhash = ((uid)mgr->nlatchpage << mgr->page_bits) / sizeof(BtHashEntry);

        mgr->nlatchpage += nodemax;             // size of the buffer pool in pages
        mgr->nlatchpage += (sizeof(BtLatchSet) * nodemax + mgr->page_size - 1)/mgr->page_size;
        mgr->latchtotal = nodemax;

        if( !initit )
                goto mgrlatch;

        // initialize an empty b-tree with latch page, root page, page of leaves
        // and page(s) of latches and page pool cache

        memset (pagezero, 0, 1 << bits);
        pagezero->alloc->bits = mgr->page_bits;
        bt_putid(pagezero->alloc->right, MIN_lvl+1);

        if( bt_writepage (mgr, pagezero->alloc, 0) ) {
                fprintf (stderr, "Unable to create btree page zero\n");
                return bt_mgrclose (mgr), NULL;
        }

        memset (pagezero, 0, 1 << bits);
        pagezero->alloc->bits = mgr->page_bits;

        for( lvl=MIN_lvl; lvl--; ) {
                slotptr(pagezero->alloc, 1)->off = mgr->page_size - 3 - (lvl ? BtId + sizeof(BtVal): sizeof(BtVal));
                key = keyptr(pagezero->alloc, 1);
                key->len = 2;           // create stopper key
                key->key[0] = 0xff;
                key->key[1] = 0xff;

                bt_putid(value, MIN_lvl - lvl + 1);
                val = valptr(pagezero->alloc, 1);
                val->len = lvl ? BtId : 0;
                memcpy (val->value, value, val->len);

                pagezero->alloc->min = slotptr(pagezero->alloc, 1)->off;
                pagezero->alloc->lvl = lvl;
                pagezero->alloc->cnt = 1;
                pagezero->alloc->act = 1;

                if( bt_writepage (mgr, pagezero->alloc, MIN_lvl - lvl) ) {
                        fprintf (stderr, "Unable to create btree page zero\n");
                        return bt_mgrclose (mgr), NULL;
                }
        }

mgrlatch:
#ifdef unix
        free (pagezero);
#else
        VirtualFree (pagezero, 0, MEM_RELEASE);
#endif
#ifdef unix
        // mlock the pagezero page

        flag = PROT_READ | PROT_WRITE;
        mgr->pagezero = mmap (0, mgr->page_size, flag, MAP_SHARED, mgr->idx, ALLOC_page << mgr->page_bits);
        if( mgr->pagezero == MAP_FAILED ) {
                fprintf (stderr, "Unable to mmap btree page zero, error = %d\n", errno);
                return bt_mgrclose (mgr), NULL;
        }
        mlock (mgr->pagezero, mgr->page_size);

        mgr->hashtable = (void *)mmap (0, (uid)mgr->nlatchpage << mgr->page_bits, flag, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
        if( mgr->hashtable == MAP_FAILED ) {
                fprintf (stderr, "Unable to mmap anonymous buffer pool pages, error = %d\n", errno);
                return bt_mgrclose (mgr), NULL;
        }
#else
        flag = PAGE_READWRITE;
        mgr->halloc = CreateFileMapping(mgr->idx, NULL, flag, 0, mgr->page_size, NULL);
        if( !mgr->halloc ) {
                fprintf (stderr, "Unable to create page zero memory mapping, error = %d\n", GetLastError());
                return bt_mgrclose (mgr), NULL;
        }

        flag = FILE_MAP_WRITE;
        mgr->pagezero = MapViewOfFile(mgr->halloc, flag, 0, 0, mgr->page_size);
        if( !mgr->pagezero ) {
                fprintf (stderr, "Unable to map page zero, error = %d\n", GetLastError());
                return bt_mgrclose (mgr), NULL;
        }

        flag = PAGE_READWRITE;
        size = (uid)mgr->nlatchpage << mgr->page_bits;
        mgr->hpool = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, flag, size >> 32, size, NULL);
        if( !mgr->hpool ) {
                fprintf (stderr, "Unable to create buffer pool memory mapping, error = %d\n", GetLastError());
                return bt_mgrclose (mgr), NULL;
        }

        flag = FILE_MAP_WRITE;
        mgr->hashtable = MapViewOfFile(mgr->pool, flag, 0, 0, size);
        if( !mgr->hashtable ) {
                fprintf (stderr, "Unable to map buffer pool, error = %d\n", GetLastError());
                return bt_mgrclose (mgr), NULL;
        }
#endif

        mgr->pagepool = (unsigned char *)mgr->hashtable + ((uid)(mgr->nlatchpage - mgr->latchtotal) << mgr->page_bits);
        mgr->latchsets = (BtLatchSet *)(mgr->pagepool - (uid)mgr->latchtotal * sizeof(BtLatchSet));

        return mgr;
}

//      open BTree access method
//      based on buffer manager

BtDb *bt_open (BtMgr *mgr)
{
BtDb *bt = malloc (sizeof(*bt));

        memset (bt, 0, sizeof(*bt));
        bt->mgr = mgr;
#ifdef unix
        bt->mem = valloc (2 *mgr->page_size);
#else
        bt->mem = VirtualAlloc(NULL, 2 * mgr->page_size, MEM_COMMIT, PAGE_READWRITE);
#endif
        bt->frame = (BtPage)bt->mem;
        bt->cursor = (BtPage)(bt->mem + 1 * mgr->page_size);
        return bt;
}

//  compare two keys, return > 0, = 0, or < 0
//  =0: keys are same
//  -1: key2 > key1
//  +1: key2 < key1
//  as the comparison value

int keycmp (BtKey* key1, unsigned char *key2, uint len2)
{
uint len1 = key1->len;
int ans;

        if( ans = memcmp (key1->key, key2, len1 > len2 ? len2 : len1) )
                return ans;

        if( len1 > len2 )
                return 1;
        if( len1 < len2 )
                return -1;

        return 0;
}

// place write, read, or parent lock on requested page_no.

void bt_lockpage(BtLock mode, BtLatchSet *set)
{
        switch( mode ) {
        case BtLockRead:
                ReadLock (set->readwr);
                break;
        case BtLockWrite:
                WriteLock (set->readwr);
                break;
        case BtLockAccess:
                ReadLock (set->access);
                break;
        case BtLockDelete:
                WriteLock (set->access);
                break;
        case BtLockParent:
                WriteLock (set->parent);
                break;
        case BtLockAtomic:
                WriteLock (set->atomic);
                break;
        case BtLockAtomic | BtLockRead:
                WriteLock (set->atomic);
                ReadLock (set->readwr);
                break;
        }
}

// remove write, read, or parent lock on requested page

void bt_unlockpage(BtLock mode, BtLatchSet *set)
{
        switch( mode ) {
        case BtLockRead:
                ReadRelease (set->readwr);
                break;
        case BtLockWrite:
                WriteRelease (set->readwr);
                break;
        case BtLockAccess:
                ReadRelease (set->access);
                break;
        case BtLockDelete:
                WriteRelease (set->access);
                break;
        case BtLockParent:
                WriteRelease (set->parent);
                break;
        case BtLockAtomic:
                memset (&set->atomictid, 0, sizeof(set->atomictid));
                WriteRelease (set->atomic);
                break;
        case BtLockAtomic | BtLockRead:
                ReadRelease (set->readwr);
                memset (&set->atomictid, 0, sizeof(set->atomictid));
                WriteRelease (set->atomic);
                break;
        }
}

//      allocate a new page
//      return with page latched, but unlocked.

int bt_newpage(BtDb *bt, BtPageSet *set, BtPage contents)
{
uid page_no;
int blk;

        //      lock allocation page

        bt_spinwritelock(bt->mgr->lock);

        // use empty chain first
        // else allocate empty page

        if( page_no = bt_getid(bt->mgr->pagezero->chain) ) {
                if( set->latch = bt_pinlatch (bt, page_no, 1) )
                        set->page = bt_mappage (bt, set->latch);
                else
                        return bt->err = BTERR_struct, -1;

                bt_putid(bt->mgr->pagezero->chain, bt_getid(set->page->right));
                bt_spinreleasewrite(bt->mgr->lock);

                memcpy (set->page, contents, bt->mgr->page_size);
                set->latch->dirty = 1;
                return 0;
        }

        page_no = bt_getid(bt->mgr->pagezero->alloc->right);
        bt_putid(bt->mgr->pagezero->alloc->right, page_no+1);

        // unlock allocation latch

        bt_spinreleasewrite(bt->mgr->lock);

        //      don't load cache from btree page

        if( set->latch = bt_pinlatch (bt, page_no, 0) )
                set->page = bt_mappage (bt, set->latch);
        else
                return bt->err = BTERR_struct;

        memcpy (set->page, contents, bt->mgr->page_size);
        set->latch->dirty = 1;
        return 0;
}

//  find slot in page for given key at a given level

int bt_findslot (BtPageSet *set, unsigned char *key, uint len)
{
uint diff, higher = set->page->cnt, low = 1, slot;
uint good = 0;

        //        make stopper key an infinite fence value

        if( bt_getid (set->page->right) )
                higher++;
        else
                good++;

        //      low is the lowest candidate.
        //  loop ends when they meet

        //  higher is already
        //      tested as .ge. the passed key.

        while( diff = higher - low ) {
                slot = low + ( diff >> 1 );
                if( keycmp (keyptr(set->page, slot), key, len) < 0 )
                        low = slot + 1;
                else
                        higher = slot, good++;
        }

        //      return zero if key is on right link page

        return good ? higher : 0;
}

//  find and load page at given level for given key
//      leave page rd or wr locked as requested

int bt_loadpage (BtDb *bt, BtPageSet *set, unsigned char *key, uint len, uint lvl, BtLock lock)
{
uid page_no = ROOT_page, prevpage = 0;
uint drill = 0xff, slot;
BtLatchSet *prevlatch;
uint mode, prevmode;

  //  start at root of btree and drill down

  do {
        // determine lock mode of drill level
        mode = (drill == lvl) ? lock : BtLockRead; 

        if( !(set->latch = bt_pinlatch (bt, page_no, 1)) )
          return 0;

        // obtain access lock using lock chaining with Access mode

        if( page_no > ROOT_page )
          bt_lockpage(BtLockAccess, set->latch);

        set->page = bt_mappage (bt, set->latch);

        //      release & unpin parent page

        if( prevpage ) {
          bt_unlockpage(prevmode, prevlatch);
          bt_unpinlatch (prevlatch);
          prevpage = 0;
        }

        //      skip Atomic lock on leaf page if already held

        if( !drill )
         if( mode & BtLockAtomic )
          if( pthread_equal (set->latch->atomictid, pthread_self()) )
                mode &= ~BtLockAtomic;

        // obtain mode lock using lock chaining through AccessLock

        bt_lockpage(mode, set->latch);

        if( mode & BtLockAtomic )
                set->latch->atomictid = pthread_self();

        if( set->page->free )
                return bt->err = BTERR_struct, 0;

        if( page_no > ROOT_page )
          bt_unlockpage(BtLockAccess, set->latch);

        // re-read and re-lock root after determining actual level of root

        if( set->page->lvl != drill) {
                if( set->latch->page_no != ROOT_page )
                        return bt->err = BTERR_struct, 0;
                        
                drill = set->page->lvl;

                if( lock != BtLockRead && drill == lvl ) {
                  bt_unlockpage(mode, set->latch);
                  bt_unpinlatch (set->latch);
                  continue;
                }
        }

        prevpage = set->latch->page_no;
        prevlatch = set->latch;
        prevmode = mode;

        //  find key on page at this level
        //  and descend to requested level

        if( set->page->kill )
          goto slideright;

        if( slot = bt_findslot (set, key, len) ) {
          if( drill == lvl )
                return slot;

          while( slotptr(set->page, slot)->dead )
                if( slot++ < set->page->cnt )
                        continue;
                else
                        goto slideright;

          page_no = bt_getid(valptr(set->page, slot)->value);
          drill--;
          continue;
        }

        //  or slide right into next page

slideright:
        page_no = bt_getid(set->page->right);

  } while( page_no );

  // return error on end of right chain

  bt->err = BTERR_struct;
  return 0;     // return error
}

//      return page to free list
//      page must be delete & write locked

void bt_freepage (BtDb *bt, BtPageSet *set)
{
        //      lock allocation page

        bt_spinwritelock (bt->mgr->lock);

        //      store chain

        memcpy(set->page->right, bt->mgr->pagezero->chain, BtId);
        bt_putid(bt->mgr->pagezero->chain, set->latch->page_no);
        set->latch->dirty = 1;
        set->page->free = 1;

        // unlock released page

        bt_unlockpage (BtLockDelete, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);

        // unlock allocation page

        bt_spinreleasewrite (bt->mgr->lock);
}

//      a fence key was deleted from a page
//      push new fence value upwards

BTERR bt_fixfence (BtDb *bt, BtPageSet *set, uint lvl)
{
unsigned char leftkey[BT_keyarray], rightkey[BT_keyarray];
unsigned char value[BtId];
BtKey* ptr;
uint idx;

        //      remove the old fence value

        ptr = keyptr(set->page, set->page->cnt);
        memcpy (rightkey, ptr, ptr->len + sizeof(BtKey));
        memset (slotptr(set->page, set->page->cnt--), 0, sizeof(BtSlot));
        set->latch->dirty = 1;

        //  cache new fence value

        ptr = keyptr(set->page, set->page->cnt);
        memcpy (leftkey, ptr, ptr->len + sizeof(BtKey));

        bt_lockpage (BtLockParent, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);

        //      insert new (now smaller) fence key

        bt_putid (value, set->latch->page_no);
        ptr = (BtKey*)leftkey;

        if( bt_insertkey (bt, ptr->key, ptr->len, lvl+1, value, BtId, 1) )
          return bt->err;

        //      now delete old fence key

        ptr = (BtKey*)rightkey;

        if( bt_deletekey (bt, ptr->key, ptr->len, lvl+1) )
                return bt->err;

        bt_unlockpage (BtLockParent, set->latch);
        bt_unpinlatch(set->latch);
        return 0;
}

//      root has a single child
//      collapse a level from the tree

BTERR bt_collapseroot (BtDb *bt, BtPageSet *root)
{
BtPageSet child[1];
uid page_no;
uint idx;

  // find the child entry and promote as new root contents

  do {
        for( idx = 0; idx++ < root->page->cnt; )
          if( !slotptr(root->page, idx)->dead )
                break;

        page_no = bt_getid (valptr(root->page, idx)->value);

        if( child->latch = bt_pinlatch (bt, page_no, 1) )
                child->page = bt_mappage (bt, child->latch);
        else
                return bt->err;

        bt_lockpage (BtLockDelete, child->latch);
        bt_lockpage (BtLockWrite, child->latch);

        memcpy (root->page, child->page, bt->mgr->page_size);
        root->latch->dirty = 1;

        bt_freepage (bt, child);

  } while( root->page->lvl > 1 && root->page->act == 1 );

  bt_unlockpage (BtLockWrite, root->latch);
  bt_unpinlatch (root->latch);
  return 0;
}

//  delete a page and manage keys
//  call with page writelocked
//      returns with page unpinned

BTERR bt_deletepage (BtDb *bt, BtPageSet *set)
{
unsigned char lowerfence[BT_keyarray], higherfence[BT_keyarray];
unsigned char value[BtId];
uint lvl = set->page->lvl;
BtPageSet right[1];
uid page_no;
BtKey *ptr;

        //      cache copy of fence key
        //      to post in parent

        ptr = keyptr(set->page, set->page->cnt);
        memcpy (lowerfence, ptr, ptr->len + sizeof(BtKey));

        //      obtain lock on right page

        page_no = bt_getid(set->page->right);

        if( right->latch = bt_pinlatch (bt, page_no, 1) )
                right->page = bt_mappage (bt, right->latch);
        else
                return 0;

        bt_lockpage (BtLockWrite, right->latch);

        // cache copy of key to update

        ptr = keyptr(right->page, right->page->cnt);
        memcpy (higherfence, ptr, ptr->len + sizeof(BtKey));

        if( right->page->kill )
                return bt->err = BTERR_struct;

        // pull contents of right peer into our empty page

        memcpy (set->page, right->page, bt->mgr->page_size);
        set->latch->dirty = 1;

        // mark right page deleted and point it to left page
        //      until we can post parent updates that remove access
        //      to the deleted page.

        bt_putid (right->page->right, set->latch->page_no);
        right->latch->dirty = 1;
        right->page->kill = 1;

        bt_lockpage (BtLockParent, right->latch);
        bt_unlockpage (BtLockWrite, right->latch);

        bt_lockpage (BtLockParent, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);

        // redirect higher key directly to our new node contents

        bt_putid (value, set->latch->page_no);
        ptr = (BtKey*)higherfence;

        if( bt_insertkey (bt, ptr->key, ptr->len, lvl+1, value, BtId, 1) )
          return bt->err;

        //      delete old lower key to our node

        ptr = (BtKey*)lowerfence;

        if( bt_deletekey (bt, ptr->key, ptr->len, lvl+1) )
          return bt->err;

        //      obtain delete and write locks to right node

        bt_unlockpage (BtLockParent, right->latch);
        bt_lockpage (BtLockDelete, right->latch);
        bt_lockpage (BtLockWrite, right->latch);
        bt_freepage (bt, right);

        bt_unlockpage (BtLockParent, set->latch);
        bt_unpinlatch (set->latch);
        bt->found = 1;
        return 0;
}

//  find and delete key on page by marking delete flag bit
//  if page becomes empty, delete it from the btree

BTERR bt_deletekey (BtDb *bt, unsigned char *key, uint len, uint lvl)
{
uint slot, idx, found, fence;
BtPageSet set[1];
BtKey *ptr;
BtVal *val;

        if( slot = bt_loadpage (bt, set, key, len, lvl, BtLockWrite) )
                ptr = keyptr(set->page, slot);
        else
                return bt->err;

        // if librarian slot, advance to real slot

        if( slotptr(set->page, slot)->type == Librarian )
                ptr = keyptr(set->page, ++slot);

        fence = slot == set->page->cnt;

        // if key is found delete it, otherwise ignore request

        if( found = !keycmp (ptr, key, len) )
          if( found = slotptr(set->page, slot)->dead == 0 ) {
                val = valptr(set->page,slot);
                slotptr(set->page, slot)->dead = 1;
                set->page->garbage += ptr->len + val->len + sizeof(BtKey) + sizeof(BtVal);
                set->page->act--;

                // collapse empty slots beneath the fence

                while( idx = set->page->cnt - 1 )
                  if( slotptr(set->page, idx)->dead ) {
                        *slotptr(set->page, idx) = *slotptr(set->page, idx + 1);
                        memset (slotptr(set->page, set->page->cnt--), 0, sizeof(BtSlot));
                  } else
                        break;
          }

        //      did we delete a fence key in an upper level?

        if( found && lvl && set->page->act && fence )
          if( bt_fixfence (bt, set, lvl) )
                return bt->err;
          else
                return bt->found = found, 0;

        //      do we need to collapse root?

        if( lvl > 1 && set->latch->page_no == ROOT_page && set->page->act == 1 )
          if( bt_collapseroot (bt, set) )
                return bt->err;
          else
                return bt->found = found, 0;

        //      delete empty page

        if( !set->page->act )
                return bt_deletepage (bt, set);

        set->latch->dirty = 1;
        bt_unlockpage(BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);
        return bt->found = found, 0;
}

BtKey *bt_foundkey (BtDb *bt)
{
        return (BtKey*)(bt->key);
}

//      advance to next slot

uint bt_findnext (BtDb *bt, BtPageSet *set, uint slot)
{
BtLatchSet *prevlatch;
uid page_no;

        if( slot < set->page->cnt )
                return slot + 1;

        prevlatch = set->latch;

        if( page_no = bt_getid(set->page->right) )
          if( set->latch = bt_pinlatch (bt, page_no, 1) )
                set->page = bt_mappage (bt, set->latch);
          else
                return 0;
        else
          return bt->err = BTERR_struct, 0;

        // obtain access lock using lock chaining with Access mode

        bt_lockpage(BtLockAccess, set->latch);

        bt_unlockpage(BtLockRead, prevlatch);
        bt_unpinlatch (prevlatch);

        bt_lockpage(BtLockRead, set->latch);
        bt_unlockpage(BtLockAccess, set->latch);
        return 1;
}

//      find unique key or first duplicate key in
//      leaf level and return number of value bytes
//      or (-1) if not found.  Setup key for bt_foundkey

int bt_findkey (BtDb *bt, unsigned char *key, uint keylen, unsigned char *value, uint valmax)
{
BtPageSet set[1];
uint len, slot;
int ret = -1;
BtKey *ptr;
BtVal *val;

  if( slot = bt_loadpage (bt, set, key, keylen, 0, BtLockRead) )
   do {
        ptr = keyptr(set->page, slot);

        //      skip librarian slot place holder

        if( slotptr(set->page, slot)->type == Librarian )
                ptr = keyptr(set->page, ++slot);

        //      return actual key found

        memcpy (bt->key, ptr, ptr->len + sizeof(BtKey));
        len = ptr->len;

        if( slotptr(set->page, slot)->type == Duplicate )
                len -= BtId;

        //      not there if we reach the stopper key

        if( slot == set->page->cnt )
          if( !bt_getid (set->page->right) )
                break;

        // if key exists, return >= 0 value bytes copied
        //      otherwise return (-1)

        if( slotptr(set->page, slot)->dead )
                continue;

        if( keylen == len )
          if( !memcmp (ptr->key, key, len) ) {
                val = valptr (set->page,slot);
                if( valmax > val->len )
                        valmax = val->len;
                memcpy (value, val->value, valmax);
                ret = valmax;
          }

        break;

   } while( slot = bt_findnext (bt, set, slot) );

  bt_unlockpage (BtLockRead, set->latch);
  bt_unpinlatch (set->latch);
  return ret;
}

//      check page for space available,
//      clean if necessary and return
//      0 - page needs splitting
//      >0  new slot value

uint bt_cleanpage(BtDb *bt, BtPageSet *set, uint keylen, uint slot, uint vallen)
{
uint nxt = bt->mgr->page_size;
BtPage page = set->page;
uint cnt = 0, idx = 0;
uint max = page->cnt;
uint newslot = max;
BtKey *key;
BtVal *val;

        if( page->min >= (max+2) * sizeof(BtSlot) + sizeof(*page) + keylen + sizeof(BtKey) + vallen + sizeof(BtVal))
                return slot;

        //      skip cleanup and proceed to split
        //      if there's not enough garbage
        //      to bother with.

        if( page->garbage < nxt / 5 )
                return 0;

        memcpy (bt->frame, page, bt->mgr->page_size);

        // skip page info and set rest of page to zero

        memset (page+1, 0, bt->mgr->page_size - sizeof(*page));
        set->latch->dirty = 1;
        page->garbage = 0;
        page->act = 0;

        // clean up page first by
        // removing deleted keys

        while( cnt++ < max ) {
                if( cnt == slot )
                        newslot = idx + 2;
                if( cnt < max && slotptr(bt->frame,cnt)->dead )
                        continue;

                // copy the value across

                val = valptr(bt->frame, cnt);
                nxt -= val->len + sizeof(BtVal);
                memcpy ((unsigned char *)page + nxt, val, val->len + sizeof(BtVal));

                // copy the key across

                key = keyptr(bt->frame, cnt);
                nxt -= key->len + sizeof(BtKey);
                memcpy ((unsigned char *)page + nxt, key, key->len + sizeof(BtKey));

                // make a librarian slot

                if( idx ) {
                        slotptr(page, ++idx)->off = nxt;
                        slotptr(page, idx)->type = Librarian;
                        slotptr(page, idx)->dead = 1;
                }

                // set up the slot

                slotptr(page, ++idx)->off = nxt;
                slotptr(page, idx)->type = slotptr(bt->frame, cnt)->type;

                if( !(slotptr(page, idx)->dead = slotptr(bt->frame, cnt)->dead) )
                        page->act++;
        }

        page->min = nxt;
        page->cnt = idx;

        //      see if page has enough space now, or does it need splitting?

        if( page->min >= (idx+2) * sizeof(BtSlot) + sizeof(*page) + keylen + sizeof(BtKey) + vallen + sizeof(BtVal) )
                return newslot;

        return 0;
}

// split the root and raise the height of the btree

BTERR bt_splitroot(BtDb *bt, BtPageSet *root, BtLatchSet *right)
{  
unsigned char leftkey[BT_keyarray];
uint nxt = bt->mgr->page_size;
unsigned char value[BtId];
BtPageSet left[1];
uid left_page_no;
BtKey *ptr;
BtVal *val;

        //      save left page fence key for new root

        ptr = keyptr(root->page, root->page->cnt);
        memcpy (leftkey, ptr, ptr->len + sizeof(BtKey));

        //  Obtain an empty page to use, and copy the current
        //  root contents into it, e.g. lower keys

        if( bt_newpage(bt, left, root->page) )
                return bt->err;

        left_page_no = left->latch->page_no;
        bt_unpinlatch (left->latch);

        // preserve the page info at the bottom
        // of higher keys and set rest to zero

        memset(root->page+1, 0, bt->mgr->page_size - sizeof(*root->page));

        // insert stopper key at top of newroot page
        // and increase the root height

        nxt -= BtId + sizeof(BtVal);
        bt_putid (value, right->page_no);
        val = (BtVal *)((unsigned char *)root->page + nxt);
        memcpy (val->value, value, BtId);
        val->len = BtId;

        nxt -= 2 + sizeof(BtKey);
        slotptr(root->page, 2)->off = nxt;
        ptr = (BtKey *)((unsigned char *)root->page + nxt);
        ptr->len = 2;
        ptr->key[0] = 0xff;
        ptr->key[1] = 0xff;

        // insert lower keys page fence key on newroot page as first key

        nxt -= BtId + sizeof(BtVal);
        bt_putid (value, left_page_no);
        val = (BtVal *)((unsigned char *)root->page + nxt);
        memcpy (val->value, value, BtId);
        val->len = BtId;

        ptr = (BtKey *)leftkey;
        nxt -= ptr->len + sizeof(BtKey);
        slotptr(root->page, 1)->off = nxt;
        memcpy ((unsigned char *)root->page + nxt, leftkey, ptr->len + sizeof(BtKey));
        
        bt_putid(root->page->right, 0);
        root->page->min = nxt;          // reset lowest used offset and key count
        root->page->cnt = 2;
        root->page->act = 2;
        root->page->lvl++;

        // release and unpin root pages

        bt_unlockpage(BtLockWrite, root->latch);
        bt_unpinlatch (root->latch);

        bt_unpinlatch (right);
        return 0;
}

//  split already locked full node
//      leave it locked.
//      return pool entry for new right
//      page, unlocked

uint bt_splitpage (BtDb *bt, BtPageSet *set)
{
uint cnt = 0, idx = 0, max, nxt = bt->mgr->page_size;
uint lvl = set->page->lvl;
BtPageSet right[1];
BtKey *key, *ptr;
BtVal *val, *src;
uid right2;
uint prev;

        //  split higher half of keys to bt->frame

        memset (bt->frame, 0, bt->mgr->page_size);
        max = set->page->cnt;
        cnt = max / 2;
        idx = 0;

        while( cnt++ < max ) {
                if( slotptr(set->page, cnt)->dead && cnt < max )
                        continue;
                src = valptr(set->page, cnt);
                nxt -= src->len + sizeof(BtVal);
                memcpy ((unsigned char *)bt->frame + nxt, src, src->len + sizeof(BtVal));

                key = keyptr(set->page, cnt);
                nxt -= key->len + sizeof(BtKey);
                ptr = (BtKey*)((unsigned char *)bt->frame + nxt);
                memcpy (ptr, key, key->len + sizeof(BtKey));

                //      add librarian slot

                if( idx ) {
                        slotptr(bt->frame, ++idx)->off = nxt;
                        slotptr(bt->frame, idx)->type = Librarian;
                        slotptr(bt->frame, idx)->dead = 1;
                }

                //  add actual slot

                slotptr(bt->frame, ++idx)->off = nxt;
                slotptr(bt->frame, idx)->type = slotptr(set->page, cnt)->type;

                if( !(slotptr(bt->frame, idx)->dead = slotptr(set->page, cnt)->dead) )
                        bt->frame->act++;
        }

        bt->frame->bits = bt->mgr->page_bits;
        bt->frame->min = nxt;
        bt->frame->cnt = idx;
        bt->frame->lvl = lvl;

        // link right node

        if( set->latch->page_no > ROOT_page )
                bt_putid (bt->frame->right, bt_getid (set->page->right));

        //      get new free page and write higher keys to it.

        if( bt_newpage(bt, right, bt->frame) )
                return 0;

        memcpy (bt->frame, set->page, bt->mgr->page_size);
        memset (set->page+1, 0, bt->mgr->page_size - sizeof(*set->page));
        set->latch->dirty = 1;

        nxt = bt->mgr->page_size;
        set->page->garbage = 0;
        set->page->act = 0;
        max /= 2;
        cnt = 0;
        idx = 0;

        if( slotptr(bt->frame, max)->type == Librarian )
                max--;

        //  assemble page of smaller keys

        while( cnt++ < max ) {
                if( slotptr(bt->frame, cnt)->dead )
                        continue;
                val = valptr(bt->frame, cnt);
                nxt -= val->len + sizeof(BtVal);
                memcpy ((unsigned char *)set->page + nxt, val, val->len + sizeof(BtVal));

                key = keyptr(bt->frame, cnt);
                nxt -= key->len + sizeof(BtKey);
                memcpy ((unsigned char *)set->page + nxt, key, key->len + sizeof(BtKey));

                //      add librarian slot

                if( idx ) {
                        slotptr(set->page, ++idx)->off = nxt;
                        slotptr(set->page, idx)->type = Librarian;
                        slotptr(set->page, idx)->dead = 1;
                }

                //      add actual slot

                slotptr(set->page, ++idx)->off = nxt;
                slotptr(set->page, idx)->type = slotptr(bt->frame, cnt)->type;
                set->page->act++;
        }

        bt_putid(set->page->right, right->latch->page_no);
        set->page->min = nxt;
        set->page->cnt = idx;

        return right->latch->entry;
}

//      fix keys for newly split page
//      call with page locked, return
//      unlocked

BTERR bt_splitkeys (BtDb *bt, BtPageSet *set, BtLatchSet *right)
{
unsigned char leftkey[BT_keyarray], rightkey[BT_keyarray];
unsigned char value[BtId];
uint lvl = set->page->lvl;
BtPage page;
BtKey *ptr;

        // if current page is the root page, split it

        if( set->latch->page_no == ROOT_page )
                return bt_splitroot (bt, set, right);

        ptr = keyptr(set->page, set->page->cnt);
        memcpy (leftkey, ptr, ptr->len + sizeof(BtKey));

        page = bt_mappage (bt, right);

        ptr = keyptr(page, page->cnt);
        memcpy (rightkey, ptr, ptr->len + sizeof(BtKey));

        // insert new fences in their parent pages

        bt_lockpage (BtLockParent, right);

        bt_lockpage (BtLockParent, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);

        // insert new fence for reformulated left block of smaller keys

        bt_putid (value, set->latch->page_no);
        ptr = (BtKey *)leftkey;

        if( bt_insertkey (bt, ptr->key, ptr->len, lvl+1, value, BtId, 1) )
                return bt->err;

        // switch fence for right block of larger keys to new right page

        bt_putid (value, right->page_no);
        ptr = (BtKey *)rightkey;

        if( bt_insertkey (bt, ptr->key, ptr->len, lvl+1, value, BtId, 1) )
                return bt->err;

        bt_unlockpage (BtLockParent, set->latch);
        bt_unpinlatch (set->latch);

        bt_unlockpage (BtLockParent, right);
        bt_unpinlatch (right);
        return 0;
}

//      install new key and value onto page
//      page must already be checked for
//      adequate space

BTERR bt_insertslot (BtDb *bt, BtPageSet *set, uint slot, unsigned char *key,uint keylen, unsigned char *value, uint vallen, uint type, uint release)
{
uint idx, librarian;
BtSlot *node;
BtKey *ptr;
BtVal *val;

        //      if found slot > desired slot and previous slot
        //      is a librarian slot, use it

        if( slot > 1 )
          if( slotptr(set->page, slot-1)->type == Librarian )
                slot--;

        // copy value onto page

        set->page->min -= vallen + sizeof(BtVal);
        val = (BtVal*)((unsigned char *)set->page + set->page->min);
        memcpy (val->value, value, vallen);
        val->len = vallen;

        // copy key onto page

        set->page->min -= keylen + sizeof(BtKey);
        ptr = (BtKey*)((unsigned char *)set->page + set->page->min);
        memcpy (ptr->key, key, keylen);
        ptr->len = keylen;
        
        //      find first empty slot

        for( idx = slot; idx < set->page->cnt; idx++ )
          if( slotptr(set->page, idx)->dead )
                break;

        // now insert key into array before slot

        if( idx == set->page->cnt )
                idx += 2, set->page->cnt += 2, librarian = 2;
        else
                librarian = 1;

        set->latch->dirty = 1;
        set->page->act++;

        while( idx > slot + librarian - 1 )
                *slotptr(set->page, idx) = *slotptr(set->page, idx - librarian), idx--;

        //      add librarian slot

        if( librarian > 1 ) {
                node = slotptr(set->page, slot++);
                node->off = set->page->min;
                node->type = Librarian;
                node->dead = 1;
        }

        //      fill in new slot

        node = slotptr(set->page, slot);
        node->off = set->page->min;
        node->type = type;
        node->dead = 0;

        if( release ) {
                bt_unlockpage (BtLockWrite, set->latch);
                bt_unpinlatch (set->latch);
        }

        return 0;
}

//  Insert new key into the btree at given level.
//      either add a new key or update/add an existing one

BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint keylen, uint lvl, void *value, uint vallen, uint unique)
{
unsigned char newkey[BT_keyarray];
uint slot, idx, len, entry;
BtPageSet set[1];
BtKey *ptr, *ins;
uid sequence;
BtVal *val;
uint type;

  // set up the key we're working on

  ins = (BtKey*)newkey;
  memcpy (ins->key, key, keylen);
  ins->len = keylen;

  // is this a non-unique index value?

  if( unique )
        type = Unique;
  else {
        type = Duplicate;
        sequence = bt_newdup (bt);
        bt_putid (ins->key + ins->len + sizeof(BtKey), sequence);
        ins->len += BtId;
  }

  while( 1 ) { // find the page and slot for the current key
        if( slot = bt_loadpage (bt, set, ins->key, ins->len, lvl, BtLockWrite) )
                ptr = keyptr(set->page, slot);
        else {
                if( !bt->err )
                        bt->err = BTERR_ovflw;
                return bt->err;
        }

        // if librarian slot == found slot, advance to real slot

        if( slotptr(set->page, slot)->type == Librarian )
          if( !keycmp (ptr, key, keylen) )
                ptr = keyptr(set->page, ++slot);

        len = ptr->len;

        if( slotptr(set->page, slot)->type == Duplicate )
                len -= BtId;

        //  if inserting a duplicate key or unique key
        //      check for adequate space on the page
        //      and insert the new key before slot.

        if( unique && (len != ins->len || memcmp (ptr->key, ins->key, ins->len)) || !unique ) {
          if( !(slot = bt_cleanpage (bt, set, ins->len, slot, vallen)) )
                if( !(entry = bt_splitpage (bt, set)) )
                  return bt->err;
                else if( bt_splitkeys (bt, set, bt->mgr->latchsets + entry) )
                  return bt->err;
                else
                  continue;

          return bt_insertslot (bt, set, slot, ins->key, ins->len, value, vallen, type, 1);
        }

        // if key already exists, update value and return

        val = valptr(set->page, slot);

        if( val->len >= vallen ) {
                if( slotptr(set->page, slot)->dead )
                        set->page->act++;
                set->page->garbage += val->len - vallen;
                set->latch->dirty = 1;
                slotptr(set->page, slot)->dead = 0;
                val->len = vallen;
                memcpy (val->value, value, vallen);
                bt_unlockpage(BtLockWrite, set->latch);
                bt_unpinlatch (set->latch);
                return 0;
        }

        //      new update value doesn't fit in existing value area

        if( !slotptr(set->page, slot)->dead )
                set->page->garbage += val->len + ptr->len + sizeof(BtKey) + sizeof(BtVal);
        else {
                slotptr(set->page, slot)->dead = 0;
                set->page->act++;
        }

        if( !(slot = bt_cleanpage (bt, set, keylen, slot, vallen)) )
          if( !(entry = bt_splitpage (bt, set)) )
                return bt->err;
          else if( bt_splitkeys (bt, set, bt->mgr->latchsets + entry) )
                return bt->err;
          else
                continue;

        set->page->min -= vallen + sizeof(BtVal);
        val = (BtVal*)((unsigned char *)set->page + set->page->min);
        memcpy (val->value, value, vallen);
        val->len = vallen;

        set->latch->dirty = 1;
        set->page->min -= keylen + sizeof(BtKey);
        ptr = (BtKey*)((unsigned char *)set->page + set->page->min);
        memcpy (ptr->key, key, keylen);
        ptr->len = keylen;
        
        slotptr(set->page, slot)->off = set->page->min;
        bt_unlockpage(BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);
        return 0;
  }
  return 0;
}

typedef struct {
        uint entry;                     // latch table entry number
        uint slot:30;           // page slot number
        uint reuse:1;           // reused previous page
        uint emptied:1;         // page was emptied
} AtomicMod;

typedef struct {
        uid page_no;            // page number for split leaf
        void *next;                     // next key to insert
        uint entry;                     // latch table entry number
        unsigned char leafkey[BT_keyarray];
} AtomicKey;

//      determine actual page where key is located
//  return slot number with set page locked

uint bt_atomicpage (BtDb *bt, BtPage source, AtomicMod *locks, uint src, BtPageSet *set)
{
BtKey *key = keyptr(source,src);
uint slot = locks[src].slot;
uint entry;

        if( src > 1 && locks[src].reuse )
          entry = locks[src-1].entry, locks[src].entry = entry, slot = 0;
        else
          entry = locks[src].entry;

        if( slot ) {
                set->latch = bt->mgr->latchsets + entry;
                set->page = bt_mappage (bt, set->latch);
                return slot;
        }

        //      is locks->reuse set?
        //      if so, find where our key
        //      is located on previous page or split pages

        do {
                set->latch = bt->mgr->latchsets + entry;
                set->page = bt_mappage (bt, set->latch);

                if( slot = bt_findslot(set, key->key, key->len) )
                        return slot;

        } while( entry = set->latch->split );

        bt->err = BTERR_atomic;
        return 0;
}

BTERR bt_atomicinsert (BtDb *bt, BtPage source, AtomicMod *locks, uint src)
{
BtKey *key = keyptr(source, src);
BtVal *val = valptr(source, src);
BtLatchSet *latch;
BtPageSet set[1];
uint slot, entry;

  while( slot = bt_atomicpage (bt, source, locks, src, set) ) {
        if( slot = bt_cleanpage(bt, set, key->len, slot, val->len) )
          return bt_insertslot (bt, set, slot, key->key, key->len, val->value, val->len, slotptr(source,src)->type, 0);
        if( entry = bt_splitpage (bt, set) )
          latch = bt->mgr->latchsets + entry;
        else
          return bt->err;
        latch->split = set->latch->split;
        set->latch->split = entry;
        bt_lockpage(BtLockWrite, latch);
  }

  return bt->err = BTERR_atomic;
}

BTERR bt_atomicdelete (BtDb *bt, BtPage source, AtomicMod *locks, uint src)
{
BtKey *key = keyptr(source, src);
uint idx, entry, slot;
BtPageSet set[1];
BtKey *ptr;
BtVal *val;

        if( slot = bt_atomicpage (bt, source, locks, src, set) )
                slotptr(set->page, slot)->dead = 1;
        else
                return bt->err = BTERR_struct;

        ptr = keyptr(set->page, slot);
        val = valptr(set->page, slot);

        set->page->garbage += ptr->len + val->len + sizeof(BtKey) + sizeof(BtVal);
        set->page->act--;

        // collapse empty slots beneath the fence

        while( idx = set->page->cnt - 1 )
          if( slotptr(set->page, idx)->dead ) {
                *slotptr(set->page, idx) = *slotptr(set->page, idx + 1);
                memset (slotptr(set->page, set->page->cnt--), 0, sizeof(BtSlot));
          } else
                break;

        set->latch->dirty = 1;
        return 0;
}

//      qsort comparison function

int bt_qsortcmp (BtSlot *slot1, BtSlot *slot2, BtPage page)
{
BtKey *key1 = (BtKey *)((unsigned char *)page + slot1->off);
BtKey *key2 = (BtKey *)((unsigned char *)page + slot2->off);

        return keycmp (key1, key2->key, key2->len);
}

//      atomic modification of a batch of keys.

//      return -1 if BTERR is set
//      otherwise return slot number
//      causing the key constraint violation
//      or zero on successful completion.

int bt_atomicmods (BtDb *bt, BtPage source)
{
uint src, idx, slot, samepage, entry, next, split;
AtomicKey *head, *tail, *leaf;
BtPageSet set[1], prev[1];
unsigned char value[BtId];
BtKey *key, *ptr, *key2;
BtLatchSet *latch;
AtomicMod *locks;
int result = 0;
BtSlot temp[1];
BtPage page;
BtVal *val;
int type;

  locks = calloc (source->cnt + 1, sizeof(AtomicMod));
  head = NULL;
  tail = NULL;

  // first sort the list of keys into order to
  //    prevent deadlocks between threads.
  qsort_r (slotptr(source,1), source->cnt, sizeof(BtSlot), (__compar_d_fn_t)bt_qsortcmp, source);
/*
  for( src = 1; src++ < source->cnt; ) {
        *temp = *slotptr(source,src);
        key = keyptr (source,src);

        for( idx = src; --idx; ) {
          key2 = keyptr (source,idx);
          if( keycmp (key, key2->key, key2->len) < 0 ) {
                *slotptr(source,idx+1) = *slotptr(source,idx);
                *slotptr(source,idx) = *temp;
          } else
                break;
        }
  }
*/
  // Load the leafpage for each key
  // and determine any constraint violations

  for( src = 0; src++ < source->cnt; ) {
        key = keyptr(source, src);
        val = valptr(source, src);
        slot = 0;

        // first determine if this modification falls
        // on the same page as the previous modification
        //      note that the far right leaf page is a special case

        if( samepage = src > 1 )
          if( samepage = !bt_getid(set->page->right) || keycmp (keyptr(set->page, set->page->cnt), key->key, key->len) > 0 )
                slot = bt_findslot(set, key->key, key->len);
          else // release read on previous page
                bt_unlockpage(BtLockRead, set->latch); 

        if( !slot ) {
          slot = bt_loadpage (bt, set, key->key, key->len, 0, BtLockAtomic | BtLockRead);
          set->latch->split = 0;
        }

        if( !slot )
          return -1;

        if( !samepage ) {
          for(idx = 0; idx++ < source->cnt; )
                if( locks[idx].entry == set->latch->entry )
                  abort();
          locks[src].entry = set->latch->entry;
          locks[src].slot = slot;
          locks[src].reuse = 0;
        } else {
          locks[src].entry = 0;
          locks[src].slot = 0;
          locks[src].reuse = 1;
        }

        if( slotptr(set->page, slot)->type == Librarian )
          ptr = keyptr(set->page, ++slot);
        else
          ptr = keyptr(set->page, slot);

        switch( slotptr(source, src)->type ) {
        case Duplicate:
        case Unique:
          if( !slotptr(set->page, slot)->dead )
           if( slot < set->page->cnt || bt_getid (set->page->right) )
            if( ptr->len == key->len && !memcmp (ptr->key, key->key, key->len) ) {

                  // return constraint violation if key already exists

                  result = src;

                  while( src ) {
                        if( locks[src].entry ) {
                          set->latch = bt->mgr->latchsets + locks[src].entry;
                          bt_unlockpage(BtLockAtomic, set->latch);
                          bt_unlockpage(BtLockRead, set->latch);
                          bt_unpinlatch (set->latch);
                        }
                        src--;
                  }

                  return result;
                }

          break;

        case Delete:
          if( !slotptr(set->page, slot)->dead )
           if( ptr->len == key->len )
                if( !memcmp (ptr->key, key->key, key->len) )
              break;

          //  Key to delete doesn't exist

          result = src;

          while( src ) {
                if( locks[src].entry ) {
                  set->latch = bt->mgr->latchsets + locks[src].entry;
                  bt_unlockpage(BtLockAtomic, set->latch);
                  bt_unlockpage(BtLockRead, set->latch);
                  bt_unpinlatch (set->latch);
                }
                src--;
          }

          return result;
        }
  }

  //  unlock last loadpage lock

  if( source->cnt > 1 )
        bt_unlockpage(BtLockRead, set->latch);

  //  obtain write lock for each page

  for( src = 0; src++ < source->cnt; )
        if( locks[src].entry )
          bt_lockpage(BtLockWrite, bt->mgr->latchsets + locks[src].entry);

  // insert or delete each key

  for( src = 0; src++ < source->cnt; )
        if( slotptr(source,src)->type == Delete )
          if( bt_atomicdelete (bt, source, locks, src) )
                return -1;
          else
                continue;
          else if( bt_atomicinsert (bt, source, locks, src) )
                return -1;
          else
                continue;

  // set ParentModification and release WriteLock
  // leave empty pages locked for later processing
  // build queue of keys to insert for split pages

  for( src = 0; src++ < source->cnt; ) {
        if( locks[src].reuse )
          continue;

        prev->latch = bt->mgr->latchsets + locks[src].entry;
        prev->page = bt_mappage (bt, prev->latch);

        //  pick-up all splits from first entry
        //  save page that points to this entry

        split = next = prev->latch->split;

        if( !prev->page->act )
          locks[src].emptied = 1;

        while( entry = next ) {
          set->latch = bt->mgr->latchsets + entry;
          set->page = bt_mappage (bt, set->latch);
          next = set->latch->split;

          // delete empty previous page

          if( !prev->page->act ) {
                memcpy (prev->page, set->page, bt->mgr->page_size);
                bt_lockpage (BtLockDelete, set->latch);
                bt_freepage (bt, set);

                prev->latch->dirty = 1;

                if( prev->page->act )
                  locks[src].emptied = 0;

                continue;
          }

          // prev page is not emptied

          locks[src].emptied = 0;

          //  schedule previous fence key update

          ptr = keyptr(prev->page,prev->page->cnt);
          leaf = malloc (sizeof(AtomicKey));

          memcpy (leaf->leafkey, ptr, ptr->len + sizeof(BtKey));
          leaf->page_no = prev->latch->page_no;
          leaf->entry = prev->latch->entry;
          leaf->next = NULL;

          if( tail )
                tail->next = leaf;
          else
                head = leaf;

          latch = prev->latch;
          tail = leaf;

          // remove empty block from the split chain

          if( !set->page->act ) {
                memcpy (prev->page->right, set->page->right, BtId);
                bt_lockpage (BtLockDelete, set->latch);
                bt_freepage (bt, set);
          } else
                *prev = *set;

          bt_lockpage(BtLockParent, latch);
          bt_unlockpage(BtLockWrite, latch);
        }

        if( !prev->page->act )
                continue;

        if( !split ) {
                bt_unlockpage(BtLockWrite, prev->latch);
                continue;
        }

        //      Process last page split in chain

        ptr = keyptr(prev->page,prev->page->cnt);
        leaf = malloc (sizeof(AtomicKey));

        memcpy (leaf->leafkey, ptr, ptr->len + sizeof(BtKey));
        leaf->page_no = prev->latch->page_no;
        leaf->entry = prev->latch->entry;
        leaf->next = NULL;

        if( tail )
          tail->next = leaf;
        else
          head = leaf;

        tail = leaf;

        bt_lockpage(BtLockParent, prev->latch);
        bt_unlockpage(BtLockWrite, prev->latch);
  }
  
  // remove Atomic locks and
  // process any empty pages

  for( src = source->cnt; src; src-- ) {
        if( locks[src].reuse )
          continue;

        //  delete page emptied by our atomic action

        set->latch = bt->mgr->latchsets + locks[src].entry;
        set->page = bt_mappage (bt, set->latch);

        if( locks[src].emptied ) {
          bt_unlockpage (BtLockAtomic, set->latch);
          if( bt_deletepage (bt, set) )
                return bt->err;
          continue;
        }

        bt_unlockpage (BtLockAtomic, set->latch);

        if( !set->latch->split )
                bt_unpinlatch (set->latch);
  }

  //  add keys for any pages split during action

  if( leaf = head )
    do {
          ptr = (BtKey *)leaf->leafkey;
          bt_putid (value, leaf->page_no);

          if( bt_insertkey (bt, ptr->key, ptr->len, 1, value, BtId, 1) )
                return bt->err;

          bt_unlockpage (BtLockParent, bt->mgr->latchsets + leaf->entry);
          bt_unpinlatch (bt->mgr->latchsets + leaf->entry);
          tail = leaf->next;
          free (leaf);
        } while( leaf = tail );

  // return success

  free (locks);
  return 0;
}

//  return next slot on cursor page
//  or slide cursor right into next page

uint bt_nextkey (BtDb *bt, uint slot)
{
BtPageSet set[1];
uid right;

  do {
        right = bt_getid(bt->cursor->right);

        while( slot++ < bt->cursor->cnt )
          if( slotptr(bt->cursor,slot)->dead )
                continue;
          else if( right || (slot < bt->cursor->cnt) ) // skip infinite stopper
                return slot;
          else
                break;

        if( !right )
                break;

        bt->cursor_page = right;

        if( set->latch = bt_pinlatch (bt, right, 1) )
                set->page = bt_mappage (bt, set->latch);
        else
                return 0;

    bt_lockpage(BtLockRead, set->latch);

        memcpy (bt->cursor, set->page, bt->mgr->page_size);

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        slot = 0;

  } while( 1 );

  return bt->err = 0;
}

//  cache page of keys into cursor and return starting slot for given key

uint bt_startkey (BtDb *bt, unsigned char *key, uint len)
{
BtPageSet set[1];
uint slot;

        // cache page for retrieval

        if( slot = bt_loadpage (bt, set, key, len, 0, BtLockRead) )
          memcpy (bt->cursor, set->page, bt->mgr->page_size);
        else
          return 0;

        bt->cursor_page = set->latch->page_no;

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        return slot;
}

BtKey *bt_key(BtDb *bt, uint slot)
{
        return keyptr(bt->cursor, slot);
}

BtVal *bt_val(BtDb *bt, uint slot)
{
        return valptr(bt->cursor,slot);
}

#ifdef STANDALONE

#ifndef unix
double getCpuTime(int type)
{
FILETIME crtime[1];
FILETIME xittime[1];
FILETIME systime[1];
FILETIME usrtime[1];
SYSTEMTIME timeconv[1];
double ans = 0;

        memset (timeconv, 0, sizeof(SYSTEMTIME));

        switch( type ) {
        case 0:
                GetSystemTimeAsFileTime (xittime);
                FileTimeToSystemTime (xittime, timeconv);
                ans = (double)timeconv->wDayOfWeek * 3600 * 24;
                break;
        case 1:
                GetProcessTimes (GetCurrentProcess(), crtime, xittime, systime, usrtime);
                FileTimeToSystemTime (usrtime, timeconv);
                break;
        case 2:
                GetProcessTimes (GetCurrentProcess(), crtime, xittime, systime, usrtime);
                FileTimeToSystemTime (systime, timeconv);
                break;
        }

        ans += (double)timeconv->wHour * 3600;
        ans += (double)timeconv->wMinute * 60;
        ans += (double)timeconv->wSecond;
        ans += (double)timeconv->wMilliseconds / 1000;
        return ans;
}
#else
#include <time.h>
#include <sys/resource.h>

double getCpuTime(int type)
{
struct rusage used[1];
struct timeval tv[1];

        switch( type ) {
        case 0:
                gettimeofday(tv, NULL);
                return (double)tv->tv_sec + (double)tv->tv_usec / 1000000;

        case 1:
                getrusage(RUSAGE_SELF, used);
                return (double)used->ru_utime.tv_sec + (double)used->ru_utime.tv_usec / 1000000;

        case 2:
                getrusage(RUSAGE_SELF, used);
                return (double)used->ru_stime.tv_sec + (double)used->ru_stime.tv_usec / 1000000;
        }

        return 0;
}
#endif

void bt_poolaudit (BtMgr *mgr)
{
BtLatchSet *latch;
uint slot = 0;

        while( slot++ < mgr->latchdeployed ) {
                latch = mgr->latchsets + slot;

                if( *latch->readwr->rin & MASK )
                        fprintf(stderr, "latchset %d rwlocked for page %.8x\n", slot, latch->page_no);
                memset ((ushort *)latch->readwr, 0, sizeof(RWLock));

                if( *latch->access->rin & MASK )
                        fprintf(stderr, "latchset %d accesslocked for page %.8x\n", slot, latch->page_no);
                memset ((ushort *)latch->access, 0, sizeof(RWLock));

                if( *latch->parent->rin & MASK )
                        fprintf(stderr, "latchset %d parentlocked for page %.8x\n", slot, latch->page_no);
                memset ((ushort *)latch->parent, 0, sizeof(RWLock));

                if( latch->pin & ~CLOCK_bit ) {
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", slot, latch->page_no);
                        latch->pin = 0;
                }
        }
}

uint bt_latchaudit (BtDb *bt)
{
ushort idx, hashidx;
uid next, page_no;
BtLatchSet *latch;
uint cnt = 0;
BtKey *ptr;

        if( *(ushort *)(bt->mgr->lock) )
                fprintf(stderr, "Alloc page locked\n");
        *(ushort *)(bt->mgr->lock) = 0;

        for( idx = 1; idx <= bt->mgr->latchdeployed; idx++ ) {
                latch = bt->mgr->latchsets + idx;
                if( *latch->readwr->rin & MASK )
                        fprintf(stderr, "latchset %d rwlocked for page %.8x\n", idx, latch->page_no);
                memset ((ushort *)latch->readwr, 0, sizeof(RWLock));

                if( *latch->access->rin & MASK )
                        fprintf(stderr, "latchset %d accesslocked for page %.8x\n", idx, latch->page_no);
                memset ((ushort *)latch->access, 0, sizeof(RWLock));

                if( *latch->parent->rin & MASK )
                        fprintf(stderr, "latchset %d parentlocked for page %.8x\n", idx, latch->page_no);
                memset ((ushort *)latch->parent, 0, sizeof(RWLock));

                if( latch->pin ) {
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", idx, latch->page_no);
                        latch->pin = 0;
                }
        }

        for( hashidx = 0; hashidx < bt->mgr->latchhash; hashidx++ ) {
          if( *(ushort *)(bt->mgr->hashtable[hashidx].latch) )
                        fprintf(stderr, "hash entry %d locked\n", hashidx);

          *(ushort *)(bt->mgr->hashtable[hashidx].latch) = 0;

          if( idx = bt->mgr->hashtable[hashidx].slot ) do {
                latch = bt->mgr->latchsets + idx;
                if( latch->pin )
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", idx, latch->page_no);
          } while( idx = latch->next );
        }

        page_no = LEAF_page;

        while( page_no < bt_getid(bt->mgr->pagezero->alloc->right) ) {
        uid off = page_no << bt->mgr->page_bits;
#ifdef unix
          pread (bt->mgr->idx, bt->frame, bt->mgr->page_size, off);
#else
        DWORD amt[1];

          SetFilePointer (bt->mgr->idx, (long)off, (long*)(&off)+1, FILE_BEGIN);

          if( !ReadFile(bt->mgr->idx, bt->frame, bt->mgr->page_size, amt, NULL))
                return bt->err = BTERR_map;

          if( *amt <  bt->mgr->page_size )
                return bt->err = BTERR_map;
#endif
                if( !bt->frame->free && !bt->frame->lvl )
                        cnt += bt->frame->act;
                page_no++;
        }
                
        cnt--;  // remove stopper key
        fprintf(stderr, " Total keys read %d\n", cnt);

        bt_close (bt);
        return 0;
}

typedef struct {
        char idx;
        char *type;
        char *infile;
        BtMgr *mgr;
        int num;
} ThreadArg;

//  standalone program to index file of keys
//  then list them onto std-out

#ifdef unix
void *index_file (void *arg)
#else
uint __stdcall index_file (void *arg)
#endif
{
int line = 0, found = 0, cnt = 0, unique;
uid next, page_no = LEAF_page;  // start on first page of leaves
unsigned char key[BT_maxkey];
unsigned char txn[65536];
ThreadArg *args = arg;
int ch, len = 0, slot;
BtPageSet set[1];
uint nxt = 65536;
BtPage page;
BtKey *ptr;
BtVal *val;
BtDb *bt;
FILE *in;

        bt = bt_open (args->mgr);
        page = (BtPage)txn;

        unique = (args->type[1] | 0x20) != 'd';

        switch(args->type[0] | 0x20)
        {
        case 'a':
                fprintf(stderr, "started latch mgr audit\n");
                cnt = bt_latchaudit (bt);
                fprintf(stderr, "finished latch mgr audit, found %d keys\n", cnt);
                break;

        case 't':
                fprintf(stderr, "started TXN pennysort for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;
                          nxt -= len - 10;
                          memcpy (txn + nxt, key + 10, len - 10);
                          nxt -= 1;
                          txn[nxt] = len - 10;
                          nxt -= 10;
                          memcpy (txn + nxt, key, 10);
                          nxt -= 1;
                          txn[nxt] = 10;
                          slotptr(page,++cnt)->off  = nxt;
                          slotptr(page,cnt)->type = Unique;
                          len = 0;

                          if( cnt < 25 )
                                continue;

                          page->cnt = cnt;
                          page->act = cnt;
                          page->min = nxt;

                          if( bt_atomicmods (bt, page) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          nxt = 65536;
                          cnt = 0;

                        }
                        else if( len < BT_maxkey )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys: %d reads %d writes\n", args->infile, line, bt->reads, bt->writes);
                break;

        case 'p':
                fprintf(stderr, "started pennysort for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;

                          if( bt_insertkey (bt, key, 10, 0, key + 10, len - 10, unique) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < BT_maxkey )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys: %d reads %d writes\n", args->infile, line, bt->reads, bt->writes);
                break;

        case 'w':
                fprintf(stderr, "started indexing for %s\n", args->infile);
                if( in = fopen (args->infile, "r") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;

                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_insertkey (bt, key, len, 0, NULL, 0, unique) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < BT_maxkey )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys: %d reads %d writes\n", args->infile, line, bt->reads, bt->writes);
                break;

        case 'd':
                fprintf(stderr, "started deleting keys for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;
                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_findkey (bt, key, len, NULL, 0) < 0 )
                                fprintf(stderr, "Cannot find key for Line: %d\n", line), exit(0);
                          ptr = (BtKey*)(bt->key);
                          found++;

                          if( bt_deletekey (bt, ptr->key, ptr->len, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < BT_maxkey )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys, %d found: %d reads %d writes\n", args->infile, line, found, bt->reads, bt->writes);
                break;

        case 'f':
                fprintf(stderr, "started finding keys for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;
                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_findkey (bt, key, len, NULL, 0) == 0 )
                                found++;
                          else if( bt->err )
                                fprintf(stderr, "Error %d Syserr %d Line: %d\n", bt->err, errno, line), exit(0);
                          len = 0;
                        }
                        else if( len < BT_maxkey )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys, found %d: %d reads %d writes\n", args->infile, line, found, bt->reads, bt->writes);
                break;

        case 's':
                fprintf(stderr, "started scanning\n");
                do {
                        if( set->latch = bt_pinlatch (bt, page_no, 1) )
                                set->page = bt_mappage (bt, set->latch);
                        else
                                fprintf(stderr, "unable to obtain latch"), exit(1);
                        bt_lockpage (BtLockRead, set->latch);
                        next = bt_getid (set->page->right);

                        for( slot = 0; slot++ < set->page->cnt; )
                         if( next || slot < set->page->cnt )
                          if( !slotptr(set->page, slot)->dead ) {
                                ptr = keyptr(set->page, slot);
                                len = ptr->len;

                            if( slotptr(set->page, slot)->type == Duplicate )
                                        len -= BtId;

                                fwrite (ptr->key, len, 1, stdout);
                                val = valptr(set->page, slot);
                                fwrite (val->value, val->len, 1, stdout);
                                fputc ('\n', stdout);
                                cnt++;
                           }

                        bt_unlockpage (BtLockRead, set->latch);
                        bt_unpinlatch (set->latch);
                } while( page_no = next );

                fprintf(stderr, " Total keys read %d: %d reads, %d writes\n", cnt, bt->reads, bt->writes);
                break;

        case 'c':
#ifdef unix
                posix_fadvise( bt->mgr->idx, 0, 0, POSIX_FADV_SEQUENTIAL);
#endif
                fprintf(stderr, "started counting\n");
                page_no = LEAF_page;

                while( page_no < bt_getid(bt->mgr->pagezero->alloc->right) ) {
                        if( bt_readpage (bt->mgr, bt->frame, page_no) )
                                break;

                        if( !bt->frame->free && !bt->frame->lvl )
                                cnt += bt->frame->act;

                        bt->reads++;
                        page_no++;
                }
                
                cnt--;  // remove stopper key
                fprintf(stderr, " Total keys read %d: %d reads, %d writes\n", cnt, bt->reads, bt->writes);
                break;
        }

        bt_close (bt);
#ifdef unix
        return NULL;
#else
        return 0;
#endif
}

typedef struct timeval timer;

int main (int argc, char **argv)
{
int idx, cnt, len, slot, err;
int segsize, bits = 16;
double start, stop;
#ifdef unix
pthread_t *threads;
#else
HANDLE *threads;
#endif
ThreadArg *args;
uint poolsize = 0;
float elapsed;
int num = 0;
char key[1];
BtMgr *mgr;
BtKey *ptr;
BtDb *bt;

        if( argc < 3 ) {
                fprintf (stderr, "Usage: %s idx_file Read/Write/Scan/Delete/Find [page_bits buffer_pool_size line_numbers src_file1 src_file2 ... ]\n", argv[0]);
                fprintf (stderr, "  where page_bits is the page size in bits\n");
                fprintf (stderr, "  buffer_pool_size is the number of pages in buffer pool\n");
                fprintf (stderr, "  line_numbers = 1 to append line numbers to keys\n");
                fprintf (stderr, "  src_file1 thru src_filen are files of keys separated by newline\n");
                exit(0);
        }

        start = getCpuTime(0);

        if( argc > 3 )
                bits = atoi(argv[3]);

        if( argc > 4 )
                poolsize = atoi(argv[4]);

        if( !poolsize )
                fprintf (stderr, "Warning: no mapped_pool\n");

        if( argc > 5 )
                num = atoi(argv[5]);

        cnt = argc - 6;
#ifdef unix
        threads = malloc (cnt * sizeof(pthread_t));
#else
        threads = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, cnt * sizeof(HANDLE));
#endif
        args = malloc (cnt * sizeof(ThreadArg));

        mgr = bt_mgr ((argv[1]), bits, poolsize);

        if( !mgr ) {
                fprintf(stderr, "Index Open Error %s\n", argv[1]);
                exit (1);
        }

        //      fire off threads

        for( idx = 0; idx < cnt; idx++ ) {
                args[idx].infile = argv[idx + 6];
                args[idx].type = argv[2];
                args[idx].mgr = mgr;
                args[idx].num = num;
                args[idx].idx = idx;
#ifdef unix
                if( err = pthread_create (threads + idx, NULL, index_file, args + idx) )
                        fprintf(stderr, "Error creating thread %d\n", err);
#else
                threads[idx] = (HANDLE)_beginthreadex(NULL, 65536, index_file, args + idx, 0, NULL);
#endif
        }

        //      wait for termination

#ifdef unix
        for( idx = 0; idx < cnt; idx++ )
                pthread_join (threads[idx], NULL);
#else
        WaitForMultipleObjects (cnt, threads, TRUE, INFINITE);

        for( idx = 0; idx < cnt; idx++ )
                CloseHandle(threads[idx]);

#endif
        bt_poolaudit(mgr);
        bt_mgrclose (mgr);

        elapsed = getCpuTime(0) - start;
        fprintf(stderr, " real %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
        elapsed = getCpuTime(1);
        fprintf(stderr, " user %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
        elapsed = getCpuTime(2);
        fprintf(stderr, " sys  %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
}

#endif  //STANDALONE