Add multi/thread multi-process threadskv10h.c

[btree] / threadskv2.c

// btree version threadskv2 sched_yield version
//      with reworked bt_deletekey code
//      phase-fair reader writer lock
//      generalized key-value interface
//
//      reworked btree node as red/black binomial tree
// 27 AUG 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/mman.h>
#include <errno.h>
#include <pthread.h>
#else
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdio.h>
#include <stdlib.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_latchtable   128                                     // number of latch manager slots

#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

#define BT_binomial             5                                       // number of levels to emit together
/*
There are five lock types for each node in three 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. 
*/

typedef enum{
        BtLockAccess,
        BtLockDelete,
        BtLockRead,
        BtLockWrite,
        BtLockParent
} 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 {
        BtSpinLatch latch[1];
        volatile ushort slot;           // Latch table entry at head of chain
} BtHashEntry;

//      latch manager table structure

typedef struct {
        RWLock readwr[1];               // read/write page lock
        RWLock access[1];               // Access Intent/Page delete
        RWLock parent[1];               // Posting of fence key in parent
        BtSpinLatch busy[1];            // slot is being moved between chains
        volatile ushort next;           // next entry in hash table chain
        volatile ushort prev;           // prev entry in hash table chain
        volatile ushort pin;            // number of outstanding locks
        volatile ushort hash;           // hash slot entry is under
        volatile uid page_no;           // latch set page number
} BtLatchSet;

//      Define the length of the page and key pointers

#define BtId 6

//      Page key slot definition.

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

typedef struct {
        uint off:BT_maxbits;    // page offset for key start
        uint fence:1;                   // is tree node the fence key?
        uint red:1;                             // is tree node red?
        uint dead:1;                    // set for deleted key
        uint left, right;               // next nodes down
} 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;
        unsigned char key[1];
} *BtKey;

//      the value structure also occupies space at the upper
//      end of the page.

typedef struct {
        unsigned char len;
        unsigned char value[1];
} *BtVal;

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

typedef struct BtPage_ {
        uint cnt;                                       // count of keys in page
        uint act;                                       // count of active keys
        uint min;                                       // next key offset
        uint root;                                      // slot of root node
        unsigned char bits:7;           // page size in bits
        unsigned char free:1;           // page is on free chain
        unsigned char lvl:6;            // level of page
        unsigned char kill:1;           // page is being deleted
        unsigned char dirty:1;          // page has deleted keys
        unsigned char right[BtId];      // page number to right
} *BtPage;

//      The memory mapping pool table buffer manager entry

typedef struct {
        uid  basepage;                          // mapped base page number
        char *map;                                      // mapped memory pointer
        ushort slot;                            // slot index in this array
        ushort pin;                                     // mapped page pin counter
        void *hashprev;                         // previous pool entry for the same hash idx
        void *hashnext;                         // next pool entry for the same hash idx
#ifndef unix
        HANDLE hmap;                            // Windows memory mapping handle
#endif
} BtPool;

#define CLOCK_bit 0x8000                // bit in pool->pin

//  The loadpage interface object

typedef struct {
        uid page_no;            // current page number
        BtPage page;            // current page pointer
        BtPool *pool;           // current page pool
        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 char chain[BtId];      // head of free page_nos chain
        BtSpinLatch lock[1];            // allocation area lite latch
        ushort latchdeployed;           // highest number of latch entries deployed
        ushort nlatchpage;                      // number of latch pages at BT_latch
        ushort latchtotal;                      // number of page latch entries
        ushort latchhash;                       // number of latch hash table slots
        ushort latchvictim;                     // next latch entry to examine
        BtHashEntry table[0];           // the hash table
} BtLatchMgr;

//      The object structure for Btree access

typedef struct {
        uint page_size;                         // page size    
        uint page_bits;                         // page size in bits    
        uint seg_bits;                          // seg size in pages in bits
        uint mode;                                      // read-write mode
#ifdef unix
        int idx;
#else
        HANDLE idx;
#endif
        ushort poolcnt;                         // highest page pool node in use
        ushort poolmax;                         // highest page pool node allocated
        ushort poolmask;                        // total number of pages in mmap segment - 1
        ushort hashsize;                        // size of Hash Table for pool entries
        volatile uint evicted;          // last evicted hash table slot
        ushort *hash;                           // pool index for hash entries
        BtSpinLatch *latch;                     // latches for hash table slots
        BtLatchMgr *latchmgr;           // mapped latch page from allocation page
        BtLatchSet *latchsets;          // mapped latch set from latch pages
        BtPool *pool;                           // memory pool page segments
#ifndef unix
        HANDLE halloc;                          // allocation and latch table handle
#endif
} BtMgr;

//      red-black tree descent stack

typedef struct {
        uint slot:BT_maxbits;
        int cmp:2;                      // comparison result
} BtPathEntry;

typedef struct {
        int lvl;                        // height of the stack
        int ge;                         // last node that is >= given node
        BtPathEntry entry[BT_maxbits+2];        // stacked tree descent
} BtPathStk;

typedef struct {
        BtMgr *mgr;                     // buffer manager for thread
        unsigned char *mem;     // frame, cursor, page memory buffer
        BtPathStk path[1];      // cached frame path stack for begin/next
        BtPage cursor;          // cached frame for start/next (never mapped)
        BtPage frame;           // spare frame for the page split (never mapped)
        uint *que;                      // binomial key distribution buffer
        int found;                      // last delete or insert was found
        int base;                       // maximum binomial assignment
        int err;                        // last error
} BtDb;

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

// 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 stopper);
extern BTERR  bt_deletekey (BtDb *bt, unsigned char *key, uint len, uint lvl, uint stopper);
extern int bt_findkey    (BtDb *bt, unsigned char *key, uint keylen, unsigned char *value, uint vallen);
extern uint bt_startkey  (BtDb *bt, unsigned char *key, uint len);
extern uint bt_nextkey   (BtDb *bt);

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

//      forward definitions
uint bt_rbremovefence (BtPage page, uint slot, BtPathStk *path);

//  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);

//  BTree page number constants
#define ALLOC_page              0       // allocation & latch manager hash table
#define ROOT_page               1       // root of the btree
#define LEAF_page               2       // first page of leaves
#define LATCH_page              3       // pages for latch manager

//      Number of levels to create in a new BTree

#define MIN_lvl                 2

//  The page is allocated from low and hi ends.
//  The key slots are allocated from the bottom,
//      and are organized into a balanced binary tree.
//      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 - 65534), and up to 253 bytes
//  of key value.  Duplicate keys are discarded.
//  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

//  Groups of pages called segments from the btree are optionally
//  cached with a memory mapped pool. A hash table is used to keep
//  track of the cached segments.  This behaviour is controlled
//  by the cache block size parameter to bt_open.

//  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;
}

//      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
}

//      link latch table entry into latch hash table

void bt_latchlink (BtDb *bt, ushort hashidx, ushort victim, uid page_no)
{
BtLatchSet *set = bt->mgr->latchsets + victim;

        if( set->next = bt->mgr->latchmgr->table[hashidx].slot )
                bt->mgr->latchsets[set->next].prev = victim;

        bt->mgr->latchmgr->table[hashidx].slot = victim;
        set->page_no = page_no;
        set->hash = hashidx;
        set->prev = 0;
}

//      release latch pin

void bt_unpinlatch (BtLatchSet *set)
{
#ifdef unix
        __sync_fetch_and_add(&set->pin, -1);
#else
        _InterlockedDecrement16 (&set->pin);
#endif
}

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

BtLatchSet *bt_pinlatch (BtDb *bt, uid page_no)
{
ushort hashidx = page_no % bt->mgr->latchmgr->latchhash;
ushort slot, avail = 0, victim, idx;
BtLatchSet *set;

        //  obtain read lock on hash table entry

        bt_spinreadlock(bt->mgr->latchmgr->table[hashidx].latch);

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

        if( slot ) {
#ifdef unix
                __sync_fetch_and_add(&set->pin, 1);
#else
                _InterlockedIncrement16 (&set->pin);
#endif
        }

    bt_spinreleaseread (bt->mgr->latchmgr->table[hashidx].latch);

        if( slot )
                return set;

  //  try again, this time with write lock

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

  if( slot = bt->mgr->latchmgr->table[hashidx].slot ) do
  {
        set = bt->mgr->latchsets + slot;
        if( page_no == set->page_no )
                break;
        if( !set->pin && !avail )
                avail = slot;
  } while( slot = set->next );

  //  found our entry, or take over an unpinned one

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

        //  see if there are any unused entries
#ifdef unix
        victim = __sync_fetch_and_add (&bt->mgr->latchmgr->latchdeployed, 1) + 1;
#else
        victim = _InterlockedIncrement16 (&bt->mgr->latchmgr->latchdeployed);
#endif

        if( victim < bt->mgr->latchmgr->latchtotal ) {
                set = bt->mgr->latchsets + victim;
#ifdef unix
                __sync_fetch_and_add(&set->pin, 1);
#else
                _InterlockedIncrement16 (&set->pin);
#endif
                bt_latchlink (bt, hashidx, victim, page_no);
                bt_spinreleasewrite (bt->mgr->latchmgr->table[hashidx].latch);
                return set;
        }

#ifdef unix
        victim = __sync_fetch_and_add (&bt->mgr->latchmgr->latchdeployed, -1);
#else
        victim = _InterlockedDecrement16 (&bt->mgr->latchmgr->latchdeployed);
#endif
  //  find and reuse previous lock entry

  while( 1 ) {
#ifdef unix
        victim = __sync_fetch_and_add(&bt->mgr->latchmgr->latchvictim, 1);
#else
        victim = _InterlockedIncrement16 (&bt->mgr->latchmgr->latchvictim) - 1;
#endif
        //      we don't use slot zero

        if( victim %= bt->mgr->latchmgr->latchtotal )
                set = bt->mgr->latchsets + victim;
        else
                continue;

        //      take control of our slot
        //      from other threads

        if( set->pin || !bt_spinwritetry (set->busy) )
                continue;

        idx = set->hash;

        // try to get write lock on hash chain
        //      skip entry if not obtained
        //      or has outstanding locks

        if( !bt_spinwritetry (bt->mgr->latchmgr->table[idx].latch) ) {
                bt_spinreleasewrite (set->busy);
                continue;
        }

        if( set->pin ) {
                bt_spinreleasewrite (set->busy);
                bt_spinreleasewrite (bt->mgr->latchmgr->table[idx].latch);
                continue;
        }

        //  unlink our available victim from its hash chain

        if( set->prev )
                bt->mgr->latchsets[set->prev].next = set->next;
        else
                bt->mgr->latchmgr->table[idx].slot = set->next;

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

        bt_spinreleasewrite (bt->mgr->latchmgr->table[idx].latch);
#ifdef unix
        __sync_fetch_and_add(&set->pin, 1);
#else
        _InterlockedIncrement16 (&set->pin);
#endif
        bt_latchlink (bt, hashidx, victim, page_no);
        bt_spinreleasewrite (bt->mgr->latchmgr->table[hashidx].latch);
        bt_spinreleasewrite (set->busy);
        return set;
  }
}

void bt_mgrclose (BtMgr *mgr)
{
BtPool *pool;
uint slot;

        // release mapped pages
        //      note that slot zero is never used

        for( slot = 1; slot < mgr->poolmax; slot++ ) {
                pool = mgr->pool + slot;
                if( pool->slot )
#ifdef unix
                        munmap (pool->map, (uid)(mgr->poolmask+1) << mgr->page_bits);
#else
                {
                        FlushViewOfFile(pool->map, 0);
                        UnmapViewOfFile(pool->map);
                        CloseHandle(pool->hmap);
                }
#endif
        }

#ifdef unix
        munmap (mgr->latchsets, mgr->latchmgr->nlatchpage * mgr->page_size);
        munmap (mgr->latchmgr, 2 * mgr->page_size);
#else
        FlushViewOfFile(mgr->latchmgr, 0);
        UnmapViewOfFile(mgr->latchmgr);
        CloseHandle(mgr->halloc);
#endif
#ifdef unix
        close (mgr->idx);
        free (mgr->pool);
        free (mgr->hash);
        free ((void *)mgr->latch);
        free (mgr);
#else
        FlushFileBuffers(mgr->idx);
        CloseHandle(mgr->idx);
        GlobalFree (mgr->pool);
        GlobalFree (mgr->hash);
        GlobalFree ((void *)mgr->latch);
        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 mapped page pool (e.g. 8192)

BtMgr *bt_mgr (char *name, uint mode, uint bits, uint poolmax, uint segsize, uint hashsize)
{
uint lvl, attr, cacheblk, last, slot, idx;
uint nlatchpage, latchhash;
unsigned char value[BtId];
BtLatchMgr *latchmgr;
off64_t size;
uint amt[1];
BtMgr* mgr;
BtKey key;
BtVal val;
int flag;

#ifndef unix
SYSTEM_INFO sysinfo[1];
#endif

        // determine sanity of page size and buffer pool

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

        if( !poolmax )
                return NULL;    // must have buffer pool

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

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

        if( mgr->idx == -1 )
                return free(mgr), NULL;
        
        cacheblk = 4096;        // minimum mmap segment size for unix

#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;

        // normalize cacheblk to multiple of sysinfo->dwAllocationGranularity
        GetSystemInfo(sysinfo);
        cacheblk = sysinfo->dwAllocationGranularity;
#endif

#ifdef unix
        latchmgr = malloc (BT_maxpage);
        *amt = 0;

        // read minimum page size to get root info

        if( size = lseek (mgr->idx, 0L, 2) ) {
                if( pread(mgr->idx, latchmgr, BT_minpage, 0) == BT_minpage )
                        bits = latchmgr->alloc->bits;
                else
                        return free(mgr), free(latchmgr), NULL;
        } else if( mode == BT_ro )
                return free(latchmgr), bt_mgrclose (mgr), NULL;
#else
        latchmgr = VirtualAlloc(NULL, BT_maxpage, MEM_COMMIT, PAGE_READWRITE);
        size = GetFileSize(mgr->idx, amt);

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

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

        mgr->poolmax = poolmax;
        mgr->mode = mode;

        if( cacheblk < mgr->page_size )
                cacheblk = mgr->page_size;

        //  mask for partial memmaps

        mgr->poolmask = (cacheblk >> bits) - 1;

        //      see if requested size of pages per memmap is greater

        if( (1 << segsize) > mgr->poolmask )
                mgr->poolmask = (1 << segsize) - 1;

        mgr->seg_bits = 0;

        while( (1 << mgr->seg_bits) <= mgr->poolmask )
                mgr->seg_bits++;

        mgr->hashsize = hashsize;

#ifdef unix
        mgr->pool = calloc (poolmax, sizeof(BtPool));
        mgr->hash = calloc (hashsize, sizeof(ushort));
        mgr->latch = calloc (hashsize, sizeof(BtSpinLatch));
#else
        mgr->pool = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, poolmax * sizeof(BtPool));
        mgr->hash = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, hashsize * sizeof(ushort));
        mgr->latch = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, hashsize * sizeof(BtSpinLatch));
#endif

        if( size || *amt )
                goto mgrlatch;

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

        memset (latchmgr, 0, 1 << bits);
        nlatchpage = BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1; 
        bt_putid(latchmgr->alloc->right, MIN_lvl+1+nlatchpage);
        latchmgr->alloc->bits = mgr->page_bits;

        latchmgr->nlatchpage = nlatchpage;
        latchmgr->latchtotal = nlatchpage * (mgr->page_size / sizeof(BtLatchSet));

        //  initialize latch manager

        latchhash = (mgr->page_size - sizeof(BtLatchMgr)) / sizeof(BtHashEntry);

        //      size of hash table = total number of latchsets

        if( latchhash > latchmgr->latchtotal )
                latchhash = latchmgr->latchtotal;

        latchmgr->latchhash = latchhash;

#ifdef unix
        if( write (mgr->idx, latchmgr, mgr->page_size) < mgr->page_size )
                return bt_mgrclose (mgr), NULL;
#else
        if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                return bt_mgrclose (mgr), NULL;

        if( *amt < mgr->page_size )
                return bt_mgrclose (mgr), NULL;
#endif

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

        for( lvl=MIN_lvl; lvl--; ) {
                slotptr(latchmgr->alloc, 1)->off = mgr->page_size - 3 - (lvl ? BtId + 1: 1);
                slotptr(latchmgr->alloc, 1)->fence = 1;
                if( !lvl )
                        slotptr(latchmgr->alloc, 1)->dead = 1;
                key = keyptr(latchmgr->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(latchmgr->alloc, 1);
                val->len = lvl ? BtId : 0;
                memcpy (val->value, value, val->len);

                latchmgr->alloc->min = slotptr(latchmgr->alloc, 1)->off;
                latchmgr->alloc->root = 1;
                latchmgr->alloc->lvl = lvl;
                latchmgr->alloc->cnt = 1;
                latchmgr->alloc->act = 1;
#ifdef unix
                if( write (mgr->idx, latchmgr, mgr->page_size) < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#else
                if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;

                if( *amt < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#endif
        }

        // clear out latch manager locks
        //      and rest of pages to round out segment

        memset(latchmgr, 0, mgr->page_size);
        last = MIN_lvl + 1;

        while( last <= ((MIN_lvl + 1 + nlatchpage) | mgr->poolmask) ) {
#ifdef unix
                pwrite(mgr->idx, latchmgr, mgr->page_size, last << mgr->page_bits);
#else
                SetFilePointer (mgr->idx, last << mgr->page_bits, NULL, FILE_BEGIN);
                if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;
                if( *amt < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#endif
                last++;
        }

mgrlatch:
#ifdef unix
        // mlock the root page and the latchmgr page

        flag = PROT_READ | PROT_WRITE;
        mgr->latchmgr = mmap (0, 2 * mgr->page_size, flag, MAP_SHARED, mgr->idx, ALLOC_page * mgr->page_size);
        if( mgr->latchmgr == MAP_FAILED )
                return bt_mgrclose (mgr), NULL;
        mlock (mgr->latchmgr, 2 * mgr->page_size);

        mgr->latchsets = (BtLatchSet *)mmap (0, mgr->latchmgr->nlatchpage * mgr->page_size, flag, MAP_SHARED, mgr->idx, LATCH_page * mgr->page_size);
        if( mgr->latchsets == MAP_FAILED )
                return bt_mgrclose (mgr), NULL;
        mlock (mgr->latchsets, mgr->latchmgr->nlatchpage * mgr->page_size);
#else
        flag = PAGE_READWRITE;
        mgr->halloc = CreateFileMapping(mgr->idx, NULL, flag, 0, (BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1 + LATCH_page) * mgr->page_size, NULL);
        if( !mgr->halloc )
                return bt_mgrclose (mgr), NULL;

        flag = FILE_MAP_WRITE;
        mgr->latchmgr = MapViewOfFile(mgr->halloc, flag, 0, 0, (BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1 + LATCH_page) * mgr->page_size);
        if( !mgr->latchmgr )
                return GetLastError(), bt_mgrclose (mgr), NULL;

        mgr->latchsets = (void *)((char *)mgr->latchmgr + LATCH_page * mgr->page_size);
#endif

#ifdef unix
        free (latchmgr);
#else
        VirtualFree (latchmgr, 0, MEM_RELEASE);
#endif
        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 = malloc (3 *mgr->page_size);
#else
        bt->mem = VirtualAlloc(NULL, 3 * mgr->page_size, MEM_COMMIT, PAGE_READWRITE);
#endif
        bt->frame = (BtPage)bt->mem;
        bt->cursor = (BtPage)(bt->mem + 1 * mgr->page_size);
        bt->que = (uint *)(bt->mem + 2 * mgr->page_size);
        return bt;
}

//  compare two keys, returning > 0, = 0, or < 0
//  as the comparison value
//      -1 -> go right
//      1 -> go left

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 > 0 ? 1 : -1;

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

        return 0;
}

//      Buffer Pool mgr

// find segment in pool
// must be called with hashslot idx locked
//      return NULL if not there
//      otherwise return node

BtPool *bt_findpool(BtDb *bt, uid page_no, uint idx)
{
BtPool *pool;
uint slot;

        // compute start of hash chain in pool

        if( slot = bt->mgr->hash[idx] ) 
                pool = bt->mgr->pool + slot;
        else
                return NULL;

        page_no &= ~bt->mgr->poolmask;

        while( pool->basepage != page_no )
          if( pool = pool->hashnext )
                continue;
          else
                return NULL;

        return pool;
}

// add segment to hash table

void bt_linkhash(BtDb *bt, BtPool *pool, uid page_no, int idx)
{
BtPool *node;
uint slot;

        pool->hashprev = pool->hashnext = NULL;
        pool->basepage = page_no & ~bt->mgr->poolmask;
        pool->pin = CLOCK_bit + 1;

        if( slot = bt->mgr->hash[idx] ) {
                node = bt->mgr->pool + slot;
                pool->hashnext = node;
                node->hashprev = pool;
        }

        bt->mgr->hash[idx] = pool->slot;
}

//  map new buffer pool segment to virtual memory

BTERR bt_mapsegment(BtDb *bt, BtPool *pool, uid page_no)
{
off64_t off = (page_no & ~bt->mgr->poolmask) << bt->mgr->page_bits;
off64_t limit = off + ((bt->mgr->poolmask+1) << bt->mgr->page_bits);
int flag;

#ifdef unix
        flag = PROT_READ | ( bt->mgr->mode == BT_ro ? 0 : PROT_WRITE );
        pool->map = mmap (0, (uid)(bt->mgr->poolmask+1) << bt->mgr->page_bits, flag, MAP_SHARED, bt->mgr->idx, off);
        if( pool->map == MAP_FAILED )
                return bt->err = BTERR_map;

#else
        flag = ( bt->mgr->mode == BT_ro ? PAGE_READONLY : PAGE_READWRITE );
        pool->hmap = CreateFileMapping(bt->mgr->idx, NULL, flag, (DWORD)(limit >> 32), (DWORD)limit, NULL);
        if( !pool->hmap )
                return bt->err = BTERR_map;

        flag = ( bt->mgr->mode == BT_ro ? FILE_MAP_READ : FILE_MAP_WRITE );
        pool->map = MapViewOfFile(pool->hmap, flag, (DWORD)(off >> 32), (DWORD)off, (bt->mgr->poolmask+1) << bt->mgr->page_bits);
        if( !pool->map )
                return bt->err = BTERR_map;
#endif
        return bt->err = 0;
}

//      calculate page within pool

BtPage bt_page (BtDb *bt, BtPool *pool, uid page_no)
{
uint subpage = (uint)(page_no & bt->mgr->poolmask); // page within mapping
BtPage page;

        page = (BtPage)(pool->map + (subpage << bt->mgr->page_bits));
//      madvise (page, bt->mgr->page_size, MADV_WILLNEED);
        return page;
}

//  release pool pin

void bt_unpinpool (BtPool *pool)
{
#ifdef unix
        __sync_fetch_and_add(&pool->pin, -1);
#else
        _InterlockedDecrement16 (&pool->pin);
#endif
}

//      find or place requested page in segment-pool
//      return pool table entry, incrementing pin

BtPool *bt_pinpool(BtDb *bt, uid page_no)
{
uint slot, hashidx, idx, victim;
BtPool *pool, *node, *next;

        //      lock hash table chain

        hashidx = (uint)(page_no >> bt->mgr->seg_bits) % bt->mgr->hashsize;
        bt_spinwritelock (&bt->mgr->latch[hashidx]);

        //      look up in hash table

        if( pool = bt_findpool(bt, page_no, hashidx) ) {
#ifdef unix
                __sync_fetch_and_or(&pool->pin, CLOCK_bit);
                __sync_fetch_and_add(&pool->pin, 1);
#else
                _InterlockedOr16 (&pool->pin, CLOCK_bit);
                _InterlockedIncrement16 (&pool->pin);
#endif
                bt_spinreleasewrite (&bt->mgr->latch[hashidx]);
                return pool;
        }

        // allocate a new pool node
        // and add to hash table

#ifdef unix
        slot = __sync_fetch_and_add(&bt->mgr->poolcnt, 1);
#else
        slot = _InterlockedIncrement16 (&bt->mgr->poolcnt) - 1;
#endif

        if( ++slot < bt->mgr->poolmax ) {
                pool = bt->mgr->pool + slot;
                pool->slot = slot;

                if( bt_mapsegment(bt, pool, page_no) )
                        return NULL;

                bt_linkhash(bt, pool, page_no, hashidx);
                bt_spinreleasewrite (&bt->mgr->latch[hashidx]);
                return pool;
        }

        // pool table is full
        //      find best pool entry to evict

#ifdef unix
        __sync_fetch_and_add(&bt->mgr->poolcnt, -1);
#else
        _InterlockedDecrement16 (&bt->mgr->poolcnt);
#endif

        while( 1 ) {
#ifdef unix
                victim = __sync_fetch_and_add(&bt->mgr->evicted, 1);
#else
                victim = _InterlockedIncrement (&bt->mgr->evicted) - 1;
#endif
                victim %= bt->mgr->poolmax;
                pool = bt->mgr->pool + victim;
                idx = (uint)(pool->basepage >> bt->mgr->seg_bits) % bt->mgr->hashsize;

                if( !victim )
                        continue;

                // try to get write lock
                //      skip entry if not obtained

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

                //      skip this entry if
                //      page is pinned
                //  or clock bit is set

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

                // unlink victim pool node from hash table

                if( node = pool->hashprev )
                        node->hashnext = pool->hashnext;
                else if( node = pool->hashnext )
                        bt->mgr->hash[idx] = node->slot;
                else
                        bt->mgr->hash[idx] = 0;

                if( node = pool->hashnext )
                        node->hashprev = pool->hashprev;

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

                //      remove old file mapping
#ifdef unix
                munmap (pool->map, (uid)(bt->mgr->poolmask+1) << bt->mgr->page_bits);
#else
//              FlushViewOfFile(pool->map, 0);
                UnmapViewOfFile(pool->map);
                CloseHandle(pool->hmap);
#endif
                pool->map = NULL;

                //  create new pool mapping
                //  and link into hash table

                if( bt_mapsegment(bt, pool, page_no) )
                        return NULL;

                bt_linkhash(bt, pool, page_no, hashidx);
                bt_spinreleasewrite (&bt->mgr->latch[hashidx]);
                return pool;
        }
}

// 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;
        }
}

// 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;
        }
}

//      allocate a new page and write page into it

uid bt_newpage(BtDb *bt, BtPage page)
{
BtPageSet set[1];
uid new_page;
int blk;

        //      lock allocation page

        bt_spinwritelock(bt->mgr->latchmgr->lock);

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

        if( new_page = bt_getid(bt->mgr->latchmgr->chain) ) {
                if( set->pool = bt_pinpool (bt, new_page) )
                        set->page = bt_page (bt, set->pool, new_page);
                else
                        return 0;

                bt_putid(bt->mgr->latchmgr->chain, bt_getid(set->page->right));
                bt_unpinpool (set->pool);
        } else {
                new_page = bt_getid(bt->mgr->latchmgr->alloc->right);
                bt_putid(bt->mgr->latchmgr->alloc->right, new_page+1);
#ifdef unix
                // if writing first page of pool block, set file length thru last page

                if( (new_page & bt->mgr->poolmask) == 0 )
                        ftruncate (bt->mgr->idx, (new_page + bt->mgr->poolmask + 1) << bt->mgr->page_bits);
#endif
        }
#ifdef unix
        // unlock allocation latch

        bt_spinreleasewrite(bt->mgr->latchmgr->lock);
#endif

        //      bring new page into pool and copy page.
        //      this will extend the file into the new pages on WIN32.

        if( set->pool = bt_pinpool (bt, new_page) )
                set->page = bt_page (bt, set->pool, new_page);
        else
                return 0;

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

#ifndef unix
        // unlock allocation latch

        bt_spinreleasewrite(bt->mgr->latchmgr->lock);
#endif
        return new_page;
}

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

uint bt_findslot (BtPage page, BtPage src, unsigned char *key, uint len, BtPathStk *path, uint stopper)
{
BtSlot *node;
uint slot;

  path->lvl = -1;
  path->ge = -1;

  if( slot = page->root ) do {
        path->entry[++path->lvl].slot = slot;
        node = slotptr(page,slot);

        if( node->fence && !bt_getid(page->right) && stopper )
          path->entry[path->lvl].cmp = 0;
        else if( node->fence && !bt_getid(page->right) )
          path->entry[path->lvl].cmp = 1;
        else if( stopper )
          path->entry[path->lvl].cmp = -1;
        else
          path->entry[path->lvl].cmp = keycmp (keyptr(src, slot), key, len);

        if( path->entry[path->lvl].cmp == 0 )
                return path->ge = path->lvl, slot;

        if( path->entry[path->lvl].cmp > 0 )
                path->ge = path->lvl, slot = node->left;
        else
                slot = node->right;
  } while( slot && path->lvl < BT_maxbits );
  else
        return 0;

  return path->entry[path->lvl].slot;
}

// return next slot on the page using the path stack

uint bt_nextslot (BtPage page, BtPathStk *path)
{
uint slot, next;
BtSlot *node;

        slot = path->entry[path->lvl].slot;
        node = slotptr(page,slot);

        if( slot = node->right ) {
          path->entry[path->lvl++].cmp = -1;
          path->entry[path->lvl].slot = slot;

          while( slot = slotptr(page,slot)->left ) {
                path->entry[path->lvl++].cmp = 1;
                path->entry[path->lvl].slot = slot;
          }

          return path->entry[path->lvl].slot;
        }

        while( path->lvl )
          if( path->entry[--path->lvl].cmp > 0 )
                return path->entry[path->lvl].slot;

        return 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, BtPathStk *path, uint stopper)
{
uid page_no = ROOT_page, prevpage = 0;
uint drill = 0xff, slot;
BtLatchSet *prevlatch;
uint mode, prevmode;
BtPool *prevpool;

  //  start at root of btree and drill down

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

        set->latch = bt_pinlatch (bt, page_no);
        set->page_no = page_no;

        // pin page contents

        if( set->pool = bt_pinpool (bt, page_no) )
                set->page = bt_page (bt, set->pool, page_no);
        else
                return 0;

        // obtain access lock using lock chaining with Access mode

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

        //      release & unpin parent page

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

        // obtain read lock using lock chaining

        bt_lockpage(mode, set->latch);

        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->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);
                  bt_unpinpool (set->pool);
                  continue;
                }
        }

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

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

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

        slot = bt_findslot (set->page, set->page, key, len, path, stopper);

        if( path->ge < 0 )
          goto slideright;

        if( drill == lvl )
          return slot;

        slot = path->entry[path->ge].slot;
        path->lvl = path->ge;

        while( slotptr(set->page, slot)->dead )
          if( slot = bt_nextslot (set->page, path) )
                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->latchmgr->lock);

        //      store chain
        memcpy(set->page->right, bt->mgr->latchmgr->chain, BtId);
        bt_putid(bt->mgr->latchmgr->chain, set->page_no);
        set->page->free = 1;

        // unlock released page

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

        // unlock allocation page

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

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

BTERR bt_fixfence (BtDb *bt, BtPageSet *set, uint lvl)
{
unsigned char leftkey[256], rightkey[256];
unsigned char value[BtId];
BtPathStk path[1];
uint slot, fence;
uid page_no;
BtKey ptr;

        //      remove the old fence value

        fence = set->page->root;
        slot = set->page->root;
        path->lvl = -1;

        do path->entry[++path->lvl].slot = fence = slot;
        while( slot = slotptr(set->page,slot)->right );

        ptr = keyptr(set->page, fence);
        memcpy (rightkey, ptr, ptr->len + 1);

        do fence = bt_rbremovefence (set->page, fence, path);
        while( slotptr(set->page,fence)->dead );

        set->page->dirty = 1;

        ptr = keyptr(set->page, fence);
        memcpy (leftkey, ptr, ptr->len + 1);
        page_no = set->page_no;

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

        //      insert new (now smaller) fence key

        bt_putid (value, page_no);

        if( bt_insertkey (bt, leftkey+1, *leftkey, lvl+1, value, BtId, 0) )
          return bt->err;

        //      now delete old fence key

        if( bt_deletekey (bt, rightkey+1, *rightkey, lvl+1, !bt_getid (set->page->right)) )
                return bt->err;

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

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

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

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

  do {
        slot = root->page->root;
        child->page_no = bt_getid (valptr(root->page, slot)->value);

        child->latch = bt_pinlatch (bt, child->page_no);
        bt_lockpage (BtLockDelete, child->latch);
        bt_lockpage (BtLockWrite, child->latch);

        if( child->pool = bt_pinpool (bt, child->page_no) )
                child->page = bt_page (bt, child->pool, child->page_no);
        else
                return bt->err;

        memcpy (root->page, child->page, bt->mgr->page_size);
        bt_freepage (bt, child);

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

  bt_unlockpage (BtLockWrite, root->latch);
  bt_unpinlatch (root->latch);
  bt_unpinpool (root->pool);
  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 stopper)
{
unsigned char lowerfence[256], higherfence[256];
uint slot, idx, dirty = 0, fence, found;
BtPageSet set[1], right[1];
unsigned char value[BtId];
BtPathStk path[1];
BtSlot *node;
BtKey ptr;
BtVal val;

        if( slot = bt_loadpage (bt, set, key, len, lvl, BtLockWrite, path, stopper) )
                node = slotptr(set->page, slot);
        else
                return bt->err;

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

        if( found = !path->entry[path->lvl].cmp )
          if( found = node->dead == 0 ) {
                dirty = node->dead = 1;
                set->page->dirty = 1;
                set->page->act--;
          }

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

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

        //      is this a collapsed root?

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

        //      return if page is not empty

        if( set->page->act ) {
                bt_unlockpage(BtLockWrite, set->latch);
                bt_unpinlatch (set->latch);
                bt_unpinpool (set->pool);
                return bt->found = found, 0;
        }

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

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

        while( slot = slotptr(set->page,slot)->right )
                fence = slot;

        ptr = keyptr(set->page, fence);
        memcpy (lowerfence, ptr, ptr->len + 1);

        //      obtain lock on right page

        right->page_no = bt_getid(set->page->right);
        right->latch = bt_pinlatch (bt, right->page_no);
        bt_lockpage (BtLockWrite, right->latch);

        // pin page contents

        if( right->pool = bt_pinpool (bt, right->page_no) )
                right->page = bt_page (bt, right->pool, right->page_no);
        else
                return 0;

        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);

        // cache copy of key to update

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

        while( slot = slotptr(set->page,slot)->right )
                fence = slot;

        ptr = keyptr(right->page, fence);
        memcpy (higherfence, ptr, ptr->len + 1);

        // mark right page deleted and point it to left page
        //      until we can post parent updates

        bt_putid (right->page->right, set->page_no);
        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

        stopper = !bt_getid (set->page->right);
        bt_putid (value, set->page_no);

        if( bt_insertkey (bt, higherfence+1, *higherfence, lvl+1, value, BtId, stopper) )
          return bt->err;

        //      delete old lower key to our node

        if( bt_deletekey (bt, lowerfence+1, *lowerfence, lvl+1, 0) )
          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_unpinpool (set->pool);
        bt->found = found;
        return 0;
}

//      find key in leaf level and return number of value bytes
//      or (-1) if not found

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

        if( !(slot = bt_loadpage (bt, set, key, keylen, 0, BtLockRead, path, 0)) )
                return -1;

        // if key exists, return TRUE
        //      otherwise return FALSE

        if( !slotptr(set->page, slot)->dead && !path->entry[path->lvl].cmp ) {
                val = valptr (set->page,slot);
                if( valmax > val->len )
                        valmax = val->len;
                memcpy (value, val->value, valmax);
                ret = valmax;
        } else
                ret = -1;

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

//      left rotate parent node

void bt_leftrotate (BtPage page, uint slot, BtSlot *parent, int cmp)
{
BtSlot *x = slotptr(page,slot);
uint right = x->right;
BtSlot *y = slotptr(page,right);

        x->right = y->left;

        if( !parent ) //        is x the root node?
                page->root = right;
        else if( cmp == 1 )
                parent->left = right;
        else
                parent->right = right;

        y->left = slot;
}

//      right rotate parent node

void bt_rightrotate (BtPage page, uint slot, BtSlot *parent, int cmp)
{
BtSlot *x = slotptr(page,slot);
uint left = x->left;
BtSlot *y = slotptr(page,left);

        x->left = y->right;

        if( !parent ) //        is y the root node?
                page->root = left;
        else if( cmp == 1 )
                parent->left = left;
        else
                parent->right = left;

        y->right = slot;
}

//      delete fence slot from rbtree at path point
//      return with new fence slot

uint bt_rbremovefence (BtPage page, uint slot, BtPathStk *path)
{
BtSlot *node = slotptr (page,slot), *parent, *sibling, *grand;
uint red = node->red, lvl, fence, idx, left;

        if( lvl =  path->lvl ) {
                parent = slotptr(page,path->entry[lvl - 1].slot);
                parent->right = node->left;
        } else
                page->root = node->left;

        if( fence = node->left )
                node = slotptr(page,fence);
        else {
                parent->fence = 1;
                return path->entry[--path->lvl].slot;
        }

        //  extend path to new fence

        path->entry[page->lvl].slot = fence;

        while( slot = slotptr(page, fence)->right )
                path->entry[++page->lvl].slot = fence = slot;

        slotptr(page,fence)->fence = 1;

        //      fixup colors

        if( !red )
         while( !node->red && lvl ) {
                left = parent->left;
                sibling = slotptr(page,left);
                if( sibling->red ) {
                  sibling->red = 0;
                  parent->red = 1;
                  if( lvl > 1 )
                        grand = slotptr(page,path->entry[lvl-2].slot);
                  else
                        grand = NULL;
                  bt_rightrotate(page, path->entry[lvl-1].slot, grand, -1);
                  sibling = slotptr(page,parent->left);

                  for( idx = ++path->lvl; idx > lvl - 1; idx-- )
                        path->entry[idx].slot = path->entry[idx-1].slot;

                  path->entry[idx].slot = left; 
                }

                if( !sibling->right || !slotptr(page,sibling->right)->red )
                  if( !sibling->left || !slotptr(page,sibling->left)->red ) {
                        sibling->red = 1;
                        node = parent;
                        parent = grand;
                        lvl--;
                        continue;
                  }

                if( !sibling->left || !slotptr(page,sibling->left)->red ) {
                        if( sibling->right )
                          slotptr(page,sibling->right)->red = 0;

                        sibling->red = 1;
                        bt_leftrotate (page, parent->left, parent, 1);
                        sibling = slotptr(page,parent->left);
                }

                slotptr(page, sibling->left)->red = 0;
                sibling->red = parent->red;
                parent->red = 0;
                bt_rightrotate(page, path->entry[lvl-1].slot, grand, -1);
                break;
         }

        slotptr(page,page->root)->red = 0;
        return fence;
}

//      insert slot into rbtree at path point

void bt_rbinsert (BtPage page, uint slot, BtPathStk *path)
{
BtSlot *parent = slotptr(page,path->entry[path->lvl].slot);
BtSlot *uncle, *grand;
int lvl = path->lvl;

        if( path->entry[lvl].cmp == 1 )
                parent->left = slot;
        else
                parent->right = slot;

        slotptr(page,slot)->red = 1;

        while( lvl > 0 && parent->red ) {
          grand = slotptr(page,path->entry[lvl-1].slot);

          if( path->entry[lvl-1].cmp == 1 ) { // was grandparent left followed?
                uncle = slotptr(page,grand->right);
                if( grand->right && uncle->red ) {
                  parent->red = 0;
                  uncle->red = 0;
                  grand->red = 1;

                  // move to grandparent & its parent (if any)

                  slot = path->entry[--lvl].slot;
                  if( !lvl )
                        break;
                  parent = slotptr(page,path->entry[--lvl].slot);
                  continue;
                }

                // was the parent right link followed?
                // if so, left rotate parent

                if( path->entry[lvl].cmp == -1 ) {
                  bt_leftrotate(page, path->entry[lvl].slot, grand, path->entry[lvl-1].cmp);
                  parent = slotptr(page,slot);  // slot was rotated to parent
                }

                parent->red = 0;
                grand->red = 1;

                //      get pointer to grandparent's parent

                if( lvl>1 )
                grand = slotptr(page,path->entry[lvl-2].slot);
                else
                        grand = NULL;

                //  right rotate the grandparent slot

                slot = path->entry[lvl-1].slot;
                bt_rightrotate(page, slot, grand, path->entry[lvl-2].cmp);
                return;
          } else {      // symmetrical case
                uncle = slotptr(page,grand->left);
                if( grand->left && uncle->red ) {
                  uncle->red = 0;
                  parent->red = 0;
                  grand->red = 1;

                  // move to grandparent & its parent (if any)
                  slot = path->entry[--lvl].slot;
                  if( !lvl )
                        break;
                  parent = slotptr(page,path->entry[--lvl].slot);
                  continue;
                }

                // was the parent left link followed?
                // if so, right rotate parent

                if( path->entry[lvl].cmp == 1 ) {
                  bt_rightrotate(page, path->entry[lvl].slot, grand, path->entry[lvl-1].cmp);
                  parent = slotptr(page,slot);  // slot was rotated to parent
                }

                parent->red = 0;
                grand->red = 1;

                //      get pointer to grandparent's parent

                if( lvl>1 )
                grand = slotptr(page,path->entry[lvl-2].slot);
                else
                        grand = NULL;

                //  left rotate the grandparent slot

                slot = path->entry[lvl-1].slot;
                bt_leftrotate(page, slot, grand, path->entry[lvl-2].cmp);
                return;
          }
        }

        //      reset root color

        slotptr(page,page->root)->red = 0;
}

//      transfer a slot from one page to another

void bt_xfrslot (BtPage page, BtPage src, uint slot, BtPathStk *path, uint copykey)
{
BtKey key = keyptr(src,slot);
BtVal val = valptr(src,slot);
BtSlot *node;

        // calculate next available slot and copy key into page

  if( copykey ) {
        page->min -= val->len + 1; // reset lowest used offset
        ((unsigned char *)page)[page->min] = val->len;
        memcpy ((unsigned char *)page + page->min +1, val->value, val->len );

        page->min -= key->len + 1; // reset lowest used offset
        ((unsigned char *)page)[page->min] = key->len;
        memcpy ((unsigned char *)page + page->min +1, key->key, key->len );
  }

  node = slotptr(page, ++page->cnt);
  node->off = copykey ? page->min : slotptr(src,slot)->off;
  node->fence = slotptr(src,slot)->fence;
  node->dead = slotptr(src,slot)->dead;

  page->act++;
  
  if( path->lvl < 0 ) {
        page->root = page->cnt;
        return;
  }

  bt_rbinsert (page, page->cnt, path);
}

//      copy keys across into a binomial tree

void bt_copykeys (BtPage page, uint slot, BtPage frame, uint *que, int lvl)
{
BtSlot *node = slotptr(page,slot);
BtKey key = ((BtKey)((unsigned char*)(frame) + node->off));
BtVal val = ((BtVal)(key->key + key->len));
uint off, nxt = page->min;
uint right = node->right;
uint left = node->left;

        // copy value

        nxt -= val->len + 1;
        ((unsigned char *)page)[nxt] = val->len;
        memcpy ((unsigned char *)page + nxt + 1, val->value, val->len);

        //      copy key

        nxt -= key->len + 1;
        memcpy ((unsigned char *)page + nxt, key, key->len + 1);
        node->off = nxt;
        page->min = nxt;

        //      punt if group of keys has filled a 4K VM block
        //      which we determine by the number of red/black
        //      levels have been copied across.

        if( lvl > BT_binomial ) {
          if( left )
                que[++(*que)] = left;
          if( right )
                que[++(*que)] = right;
          return;
        }

        if( left )
          bt_copykeys (page, left, frame, que, lvl+1);

        if( right )
          bt_copykeys (page, right, frame, que, lvl+1);
}

//      clean page and rebuild red-black tree
//      return 0 - page needs splitting
//      >0  cleanup done, try again

uint bt_cleanpage(BtDb *bt, BtPage page, uint keylen, uint vallen)
{
uint max = page->cnt;
BtPathStk path[1];
uint cnt, slot;
BtSlot *node;
uid right;
BtKey key;
BtVal val;

        //      skip cleanup if nothing to reclaim

        if( !page->dirty )
                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));
        page->min = bt->mgr->page_size;
        page->dirty = 0;
        page->root = 0;
        page->cnt = 0;
        page->act = 0;

        // try cleaning up page first
        // by removing deleted keys
        //      from the heap

        right = bt_getid (bt->frame->right);
        slot = 0;

        while( ++slot <= max ) {
                node = slotptr(bt->frame,slot);

                if( !node->off )
                        continue;

                if( page->lvl || !node->fence )
                   if( node->dead )
                        continue;

                // xfr the slot to the page b-heap using keys from bt->frame

                key = keyptr(bt->frame, slot);
                bt_findslot (page, bt->frame, key->key, key->len, path, node->fence && !right);
                bt_xfrslot (page, bt->frame, slot, path, 0);
        }

        // now copy keys & values across from bt->frame to page
        //      in blocks of BT_binomial tree levels

        page->min = bt->mgr->page_size;
        bt->que[1] = page->root;
        *bt->que = 1;
        cnt = 0;

        do bt_copykeys (page, bt->que[++cnt], bt->frame, bt->que, 0);
        while( cnt < *bt->que );

        if( page->min < (page->cnt+1) * sizeof(BtSlot) + sizeof(*page) + keylen + 1 + vallen + 1 )
                return 0;

        return 1;
}

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

BTERR bt_splitroot(BtDb *bt, BtPageSet *root, unsigned char *leftkey, uid page_no2)
{
uint nxt = bt->mgr->page_size;
unsigned char value[BtId];
BtSlot *node;
uid left;

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

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

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

        nxt -= BtId + 1;
        bt_putid (value, left);
        ((unsigned char *)root->page)[nxt] = BtId;
        memcpy ((unsigned char *)root->page + nxt + 1, value, BtId);

        nxt -= *leftkey + 1;
        memcpy ((unsigned char *)root->page + nxt, leftkey, *leftkey + 1);
        node = slotptr(root->page, 1);
        node->off = nxt;
        node->red = 1;
        
        // insert stopper key on newroot page
        // and increase the root height

        nxt -= 3 + BtId + 1;
        ((unsigned char *)root->page)[nxt] = 2;
        ((unsigned char *)root->page)[nxt+1] = 0xff;
        ((unsigned char *)root->page)[nxt+2] = 0xff;

        bt_putid (value, page_no2);
        ((unsigned char *)root->page)[nxt+3] = BtId;
        memcpy ((unsigned char *)root->page + nxt + 4, value, BtId);
        node = slotptr(root->page, 2);
        node->fence = 1;
        node->off = nxt;
        node->left = 1;

        bt_putid(root->page->right, 0);
        root->page->min = nxt;          // reset lowest used offset and key count
        root->page->root = 2;
        root->page->cnt = 2;
        root->page->act = 2;
        root->page->lvl++;

        // release and unpin root

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

//      copy sub-tree from one node to the root of another
//      return slot number in destination

uint bt_copysubtree (BtDb *bt, BtPage dest, BtPage src, uint idx, uint parent, uint off)
{
BtSlot *node = slotptr(src, idx);
uint child, slot;

        slot = parent * 2 + off;

        if( slot > bt->base )
                slot = ++dest->cnt;

        *slotptr(dest, slot) = *node;
        dest->act++;

        if( child = node->left )
          child = bt_copysubtree (bt, dest, src, child, slot, 0);

        slotptr(dest, slot)->left = child;

        if( child = node->right )
          child = bt_copysubtree (bt, dest, src, child, slot, 1);

        slotptr(dest, slot)->right = child;
        return slot;
}

//  split already locked full node
//      return unlocked.

BTERR bt_splitpage (BtDb *bt, BtPageSet *set)
{
unsigned char fencekey[256], rightkey[256];
unsigned char value[BtId];
uint lvl = set->page->lvl;
uint prev, fence, stopper;
BtPageSet right[1];
BtPathStk path[1];
uint cnt, slot;
BtSlot *node;
BtKey key;
BtVal val;

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

        slot = slotptr(set->page, set->page->root)->right;
        memset (bt->frame, 0, bt->mgr->page_size);
        bt->base = set->page->cnt / 2;
        bt->frame->cnt = bt->base;

        bt->frame->root = bt_copysubtree (bt, bt->frame, set->page, slot, 0, 1);
        bt->frame->lvl = set->page->lvl;

        // now copy keys & values across from page to bt->frame
        //      in blocks of BT_binomial tree levels

        slotptr(bt->frame,bt->frame->root)->red = 0;
        bt->frame->min = bt->mgr->page_size;
        bt->que[1] = bt->frame->root;
        *bt->que = 1;
        cnt = 0;

        do bt_copykeys (bt->frame, bt->que[++cnt], set->page, bt->que, 0);
        while( cnt < *bt->que );

        // remember existing fence key for new page to the right

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

        while( slot = slotptr(set->page,slot)->right )
                fence = slot;

        key = keyptr(set->page,fence);
        memcpy (rightkey, key, key->len + 1);

        bt->frame->bits = bt->mgr->page_bits;
        bt->frame->lvl = lvl;

        // link right node

        if( set->page_no > ROOT_page )
                memcpy (bt->frame->right, set->page->right, BtId);

        stopper = !bt_getid (bt->frame->right);

        //      get new free page and write higher keys in bt->frame to it.

        if( !(right->page_no = bt_newpage(bt, bt->frame)) )
                return bt->err;

        //      update lower keys to continue in old page

        memcpy (bt->frame, set->page, bt->mgr->page_size);
        memset (set->page+1, 0, bt->mgr->page_size - sizeof(*set->page));
        slot = slotptr(bt->frame, bt->frame->root)->left;
        set->page->cnt = bt->base;
        set->page->dirty = 0;
        set->page->act = 0;

        //  assemble page of smaller keys in set->page

        set->page->root = bt_copysubtree (bt, set->page, bt->frame, slot, 0, 1);
        set->page->min = bt->mgr->page_size;

        bt->que[1] = set->page->root;
        *bt->que = 1;
        cnt = 0;

        do bt_copykeys (set->page, bt->que[++cnt], bt->frame, bt->que, 0);
        while( cnt < *bt->que );

        bt_putid(set->page->right, right->page_no);

        //      translate old r/b root as new left fence

        key = keyptr(bt->frame,bt->frame->root);
        bt_findslot (set->page, set->page, key->key, key->len, path, 0);
        bt_xfrslot (set->page, bt->frame, bt->frame->root, path, 1);

        node = slotptr(set->page,set->page->cnt);
        memcpy(fencekey, key, key->len + 1);
        node->fence = 1;

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

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

        // insert new fences in their parent pages

        right->latch = bt_pinlatch (bt, right->page_no);
        bt_lockpage (BtLockParent, right->latch);

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

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

        bt_putid (value, set->page_no);

        if( bt_insertkey (bt, fencekey+1, *fencekey, lvl+1, value, BtId, 0) )
                return bt->err;

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

        bt_putid (value, right->page_no);

        if( bt_insertkey (bt, rightkey+1, *rightkey, lvl+1, value, BtId, stopper) )
                return bt->err;

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

        bt_unlockpage (BtLockParent, right->latch);
        bt_unpinlatch (right->latch);
        return 0;
}
//  Insert new key into the btree at given level.

BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint keylen, uint lvl, void *value, uint vallen, uint stopper)
{
BtPathStk path[1];
BtPageSet set[1];
uint slot, idx;
BtSlot *node;
uint reuse;
BtKey ptr;
BtVal val;

        while( 1 ) {
                if( slot = bt_loadpage (bt, set, key, keylen, lvl, BtLockWrite, path, stopper) )
                        node = slotptr(set->page, slot);
                else {
                        if( !bt->err )
                                bt->err = BTERR_ovflw;
                        return bt->err;
                }

                // if key already exists, update id and return

                if( reuse = !path->entry[path->lvl].cmp )
                  if( val = valptr(set->page, slot), val->len >= vallen ) {
                        if( node->dead )
                                set->page->act++;
                        node->dead = 0;
                        val->len = vallen;
                        memcpy (val->value, value, vallen);
                        bt_unlockpage(BtLockWrite, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                        return 0;
                  } else {
                        if( !node->dead )
                                set->page->act--;
                        set->page->dirty = 1;
                        node->dead = 1;
                  }

                // check if page has enough space

                if( set->page->min >= (set->page->cnt+1) * sizeof(BtSlot) + sizeof(*set->page) + keylen + 1 + vallen + 1)
                        break;

                if( bt_cleanpage (bt, set->page, keylen, vallen) ) {
                        bt_unlockpage (BtLockWrite, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                        continue;       // find new slot number
                }

                if( bt_splitpage (bt, set) )
                        return bt->err;
        }

        // calculate next available slot and copy key into page

        set->page->min -= vallen + 1; // reset lowest used offset
        ((unsigned char *)set->page)[set->page->min] = vallen;
        memcpy ((unsigned char *)set->page + set->page->min +1, value, vallen );

        set->page->min -= keylen + 1; // reset lowest used offset
        ((unsigned char *)set->page)[set->page->min] = keylen;
        memcpy ((unsigned char *)set->page + set->page->min +1, key, keylen );

        set->page->act++;

        if( !reuse ) {
                slot = ++set->page->cnt;
                node = slotptr(set->page,slot);
        }

        node->off = set->page->min;
        node->dead = 0;

        if( !reuse )
                bt_rbinsert (set->page, slot, path);

        bt_unlockpage (BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        return 0;
}

BTERR bt_startpage (BtDb *bt, uid page_no)
{
BtPageSet set[1];
BtSlot *node;
uint slot;

        if( set->pool = bt_pinpool (bt, page_no) )
                set->page = bt_page (bt, set->pool, page_no);
        else
                return 0;

        set->latch = bt_pinlatch (bt, page_no);
    bt_lockpage(BtLockRead, set->latch);

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

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);

        slot = bt->cursor->root;
        bt->path->lvl = -1;

        do {
                bt->path->entry[++bt->path->lvl].slot = slot;
                bt->path->entry[bt->path->lvl].cmp = 1;
                slot = slotptr(bt->cursor, slot)->left;
        } while( slot && bt->path->lvl < BT_maxbits );

        slot =  bt->path->entry[bt->path->lvl].slot;

        while( slot && slotptr(bt->cursor,slot)->dead )
                slot = bt_nextkey (bt);

        return slot;
}

//  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, bt->path, 0) )
          memcpy (bt->cursor, set->page, bt->mgr->page_size);
        else
          return 0;

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);

        while( bt->path->lvl && bt->path->entry[bt->path->lvl - 1].cmp < 0 )
          slot = bt->path->entry[--bt->path->lvl].slot;

        return slot;
}

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

uint bt_nextkey (BtDb *bt)
{
uid right;
uint slot;

  while( slot = bt_nextslot (bt->cursor, bt->path) )
        if( slotptr(bt->cursor,slot)->dead )
          continue;
        else
          return slot;

  if( right = bt_getid(bt->cursor->right) )
        return bt_startpage (bt, right);

  return bt->err = 0;
}

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

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

#ifdef unix
        posix_fadvise( bt->mgr->idx, 0, 0, POSIX_FADV_SEQUENTIAL);
#endif
        if( *(ushort *)(bt->mgr->latchmgr->lock) )
                fprintf(stderr, "Alloc page locked\n");
        *(ushort *)(bt->mgr->latchmgr->lock) = 0;

        for( idx = 1; idx <= bt->mgr->latchmgr->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->latchmgr->latchhash; hashidx++ ) {
          if( *(ushort *)(bt->mgr->latchmgr->table[hashidx].latch) )
                        fprintf(stderr, "hash entry %d locked\n", hashidx);

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

          if( idx = bt->mgr->latchmgr->table[hashidx].slot ) do {
                latch = bt->mgr->latchsets + idx;
                if( *(ushort *)latch->busy )
                        fprintf(stderr, "latchset %d busylocked for page %.8x\n", idx, latch->page_no);
                *(ushort *)latch->busy = 0;
                if( latch->pin )
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", idx, latch->page_no);
          } while( idx = latch->next );
        }

        next = bt->mgr->latchmgr->nlatchpage + LATCH_page;
        page_no = LEAF_page;

        while( page_no < bt_getid(bt->mgr->latchmgr->alloc->right) ) {
        off64_t 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))
                        fprintf(stderr, "page %.8x unable to read\n", page_no);

                  if( *amt <  bt->mgr->page_size )
                        fprintf(stderr, "page %.8x unable to read\n", page_no);
#endif
                if( !bt->frame->free )
                 if( !bt->frame->lvl )
                        cnt += bt->frame->act;

                if( page_no > LEAF_page )
                        next = page_no + 1;
                page_no = next;
        }
        return cnt - 1;
}

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;
uid next, page_no = LEAF_page;  // start on first page of leaves
unsigned char key[256];
ThreadArg *args = arg;
int ch, len = 0, slot;
BtKey ptr;
BtDb *bt;
FILE *in;

        bt = bt_open (args->mgr);

        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 '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, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys\n", args->infile, line);
                break;

        case 'w':
                fprintf(stderr, "started indexing 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_insertkey (bt, key, len, 0, NULL, 0, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys\n", args->infile, line);
                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_deletekey (bt, key, len, 0, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for keys, %d \n", args->infile, line);
                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 < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys, found %d\n", args->infile, line, found);
                break;

        case 's':
                fprintf(stderr, "started scanning\n");

                if( slot = bt_startpage (bt, LEAF_page) )
                  do {
                        ptr = keyptr(bt->cursor, slot);
                        fwrite (ptr->key, ptr->len, 1, stdout);
                        fputc ('\n', stdout);
                        cnt++;
                  } while( slot = bt_nextkey (bt) );

                fprintf(stderr, " Total keys read %d\n", cnt);
                break;

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

                while( page_no < bt_getid(bt->mgr->latchmgr->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;
                        if( page_no > LEAF_page )
                                next = page_no + 1;
                        page_no = next;
                }
                
                fprintf(stderr, " Total keys read %d\n", cnt);
                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 mapped_segments seg_bits line_numbers src_file1 src_file2 ... ]\n", argv[0]);
                fprintf (stderr, "  where page_bits is the page size in bits\n");
                fprintf (stderr, "  mapped_segments is the number of mmap segments in buffer pool\n");
                fprintf (stderr, "  seg_bits is the size of individual segments in buffer pool in pages in bits\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( poolsize > 65535 )
                fprintf (stderr, "Warning: mapped_pool > 65535 segments\n");

        if( argc > 5 )
                segsize = atoi(argv[5]);
        else
                segsize = 4;    // 16 pages per mmap segment

        if( argc > 6 )
                num = atoi(argv[6]);

        cnt = argc - 7;
#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]), BT_rw, bits, poolsize, segsize, poolsize / 8);

        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 + 7];
                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
        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);

        bt_mgrclose (mgr);
}

#endif  //STANDALONE