** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.158 2004/06/05 00:01:45 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
**
** If there are any outstanding cursors, this routine is a no-op.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused(Btree *pBt){
  if( pBt->inTrans==TRANS_NONE && pBt->pCursor==0 && pBt->pPage1!=0 ){






    releasePage(pBt->pPage1);
    pBt->pPage1 = 0;
    pBt->inStmt = 0;
  }
}

/*
................................................................................
*/
static void getCellInfo(BtCursor *pCur){
  if( pCur->info.nSize==0 ){
    parseCell(pCur->pPage, pCur->idx, &pCur->info);
  }else{
#ifndef NDEBUG
    CellInfo info;

    parseCell(pCur->pPage, pCur->idx, &info);
    assert( memcmp(&info, &pCur->info, sizeof(info))==0 );
#endif
  }
}

/*

** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.159 2004/06/06 00:42:26 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
**
** If there are any outstanding cursors, this routine is a no-op.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused(Btree *pBt){
  if( pBt->inTrans==TRANS_NONE && pBt->pCursor==0 && pBt->pPage1!=0 ){
    if( pBt->pPage1->aData==0 ){
      MemPage *pPage = pBt->pPage1;
      pPage->aData = &((char*)pPage)[-pBt->pageSize];
      pPage->pBt = pBt;
      pPage->pgno = 1;
    }
    releasePage(pBt->pPage1);
    pBt->pPage1 = 0;
    pBt->inStmt = 0;
  }
}

/*
................................................................................
*/
static void getCellInfo(BtCursor *pCur){
  if( pCur->info.nSize==0 ){
    parseCell(pCur->pPage, pCur->idx, &pCur->info);
  }else{
#ifndef NDEBUG
    CellInfo info;
    memset(&info, 0, sizeof(info));
    parseCell(pCur->pPage, pCur->idx, &info);
    assert( memcmp(&info, &pCur->info, sizeof(info))==0 );
#endif
  }
}

/*

#include "os_common.h"

/*
** Delete the named file
*/
int sqlite3OsDelete(const char *zFilename){
  DeleteFile(zFilename);

  return SQLITE_OK;
}

/*
** Return TRUE if the named file exists.
*/
int sqlite3OsFileExists(const char *zFilename){
................................................................................
      return SQLITE_CANTOPEN;
    }
    *pReadonly = 1;
  }else{
    *pReadonly = 0;
  }
  id->h = h;
  id->locked = 0;
  OpenCounter(+1);

  return SQLITE_OK;
}


/*
** Attempt to open a new file for exclusive access by this process.
** The file will be opened for both reading and writing.  To avoid
................................................................................
     fileflags,
     NULL
  );
  if( h==INVALID_HANDLE_VALUE ){
    return SQLITE_CANTOPEN;
  }
  id->h = h;
  id->locked = 0;
  OpenCounter(+1);

  return SQLITE_OK;
}

/*
** Attempt to open a new file for read-only access.
**
** On success, write the file handle into *id and return SQLITE_OK.
................................................................................
     FILE_ATTRIBUTE_NORMAL | FILE_FLAG_RANDOM_ACCESS,
     NULL
  );
  if( h==INVALID_HANDLE_VALUE ){
    return SQLITE_CANTOPEN;
  }
  id->h = h;
  id->locked = 0;
  OpenCounter(+1);

  return SQLITE_OK;
}

/*
** Attempt to open a file descriptor for the directory that contains a
** file.  This file descriptor can be used to fsync() the directory
** in order to make sure the creation of a new file is actually written
................................................................................
    sqlite3Randomness(15, &zBuf[j]);
    for(i=0; i<15; i++, j++){
      zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
    }
    zBuf[j] = 0;
    if( !sqlite3OsFileExists(zBuf) ) break;
  }

  return SQLITE_OK; 
}

/*
** Close a file.
*/
int sqlite3OsClose(OsFile *id){
................................................................................
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
int sqlite3OsRead(OsFile *id, void *pBuf, int amt){
  DWORD got;
  SimulateIOError(SQLITE_IOERR);
  TRACE2("READ %d\n", last_page);
  if( !ReadFile(id->h, pBuf, amt, &got, 0) ){
    got = 0;
  }
  if( got==(DWORD)amt ){
    return SQLITE_OK;
  }else{
    return SQLITE_IOERR;
................................................................................
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
int sqlite3OsWrite(OsFile *id, const void *pBuf, int amt){
  int rc;
  DWORD wrote;
  SimulateIOError(SQLITE_IOERR);
  TRACE2("WRITE %d\n", last_page);
  while( amt>0 && (rc = WriteFile(id->h, pBuf, amt, &wrote, 0))!=0 && wrote>0 ){
    amt -= wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  if( !rc || amt>(int)wrote ){
    return SQLITE_FULL;
  }
................................................................................
*/
int sqlite3OsSeek(OsFile *id, off_t offset){
  LONG upperBits = offset>>32;
  LONG lowerBits = offset & 0xffffffff;
  DWORD rc;
  SEEK(offset/1024 + 1);
  rc = SetFilePointer(id->h, lowerBits, &upperBits, FILE_BEGIN);
  /* TRACE3("SEEK rc=0x%x upper=0x%x\n", rc, upperBits); */
  return SQLITE_OK;
}

/*
** Make sure all writes to a particular file are committed to disk.
*/
int sqlite3OsSync(OsFile *id){

  if( FlushFileBuffers(id->h) ){
    return SQLITE_OK;
  }else{
    return SQLITE_IOERR;
  }
}

/*
** Truncate an open file to a specified size
*/
int sqlite3OsTruncate(OsFile *id, off_t nByte){
  LONG upperBits = nByte>>32;

  SimulateIOError(SQLITE_IOERR);
  SetFilePointer(id->h, nByte, &upperBits, FILE_BEGIN);
  SetEndOfFile(id->h);
  return SQLITE_OK;
}

/*
................................................................................
  DWORD upperBits, lowerBits;
  SimulateIOError(SQLITE_IOERR);
  lowerBits = GetFileSize(id->h, &upperBits);
  *pSize = (((off_t)upperBits)<<32) + lowerBits;
  return SQLITE_OK;
}

/*
** Return true (non-zero) if we are running under WinNT, Win2K or WinXP.
** Return false (zero) for Win95, Win98, or WinME.
**
** Here is an interesting observation:  Win95, Win98, and WinME lack
** the LockFileEx() API.  But we can still statically link against that
** API as long as we don't call it win running Win95/98/ME.  A call to
** this routine is used to determine if the host is Win95/98/ME or
** WinNT/2K/XP so that we will know whether or not we can safely call
** the LockFileEx() API.
*/
int isNT(void){
  static int osType = 0;   /* 0=unknown 1=win95 2=winNT */
  if( osType==0 ){
    OSVERSIONINFO sInfo;
    sInfo.dwOSVersionInfoSize = sizeof(sInfo);
    GetVersionEx(&sInfo);
    osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
  }
  return osType==2;
}

/*
** Windows file locking notes:
**
** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
** those functions are not available.  So we use only LockFile() and
** UnlockFile().
**
** LockFile() prevents not just writing but also reading by other processes.
** (This is a design error on the part of Windows, but there is nothing
** we can do about that.)  So the region used for locking is at the
** end of the file where it is unlikely to ever interfere with an
** actual read attempt.
**
** A database read lock is obtained by locking a single randomly-chosen 
** byte out of a specific range of bytes. The lock byte is obtained at 
** random so two separate readers can probably access the file at the 
** same time, unless they are unlucky and choose the same lock byte.
** A database write lock is obtained by locking all bytes in the range.
** There can only be one writer.
**
** A lock is obtained on the first byte of the lock range before acquiring
** either a read lock or a write lock.  This prevents two processes from
** attempting to get a lock at a same time.  The semantics of 
** sqlite3OsReadLock() require that if there is already a write lock, that
** lock is converted into a read lock atomically.  The lock on the first
** byte allows us to drop the old write lock and get the read lock without
** another process jumping into the middle and messing us up.  The same
** argument applies to sqlite3OsWriteLock().
**
** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
** which means we can use reader/writer locks.  When reader writer locks
** are used, the lock is placed on the same range of bytes that is used
** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
** will support two or more Win95 readers or two or more WinNT readers.
** But a single Win95 reader will lock out all WinNT readers and a single
** WinNT reader will lock out all other Win95 readers.
**
** The following #defines specify the range of bytes used for locking.
** N_LOCKBYTE is the number of bytes available for doing the locking.
** The first byte used to hold the lock while the lock is changing does
** not count toward this number.  FIRST_LOCKBYTE is the address of
** the first byte in the range of bytes used for locking.
*/

#define N_LOCKBYTE       10239
#define FIRST_LOCKBYTE   (0xffffffff - N_LOCKBYTE)


int sqlite3OsLock(OsFile *id, int locktype){






































  return SQLITE_OK;
}




int sqlite3OsCheckWriteLock(OsFile *id){






  return 0;
}

/*
** Change the status of the lock on the file "id" to be a readlock.
** If the file was write locked, then this reduces the lock to a read.
** If the file was read locked, then this acquires a new read lock.
**


** Return SQLITE_OK on success and SQLITE_BUSY on failure.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.

*/
int sqlite3OsReadLock(OsFile *id){
  int rc;









  if( id->locked>0 ){
    rc = SQLITE_OK;





















  }else{
    int lk;
    int res;
    int cnt = 100;
    sqlite3Randomness(sizeof(lk), &lk);
    lk = (lk & 0x7fffffff)%N_LOCKBYTE + 1;
    while( cnt-->0 && (res = LockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0))==0 ){
      Sleep(1);

    }

















    if( res ){
      UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
      if( isNT() ){
        OVERLAPPED ovlp;
        ovlp.Offset = FIRST_LOCKBYTE+1;
        ovlp.OffsetHigh = 0;
        ovlp.hEvent = 0;
        res = LockFileEx(id->h, LOCKFILE_FAIL_IMMEDIATELY, 
                          0, N_LOCKBYTE, 0, &ovlp);

      }else{
        res = LockFile(id->h, FIRST_LOCKBYTE+lk, 0, 1, 0);

      }
      UnlockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0);
    }




    if( res ){
      id->locked = lk;
      rc = SQLITE_OK;
    }else{

      rc = SQLITE_BUSY;
    }
  }
  return rc;
}

/*
** Change the lock status to be an exclusive or write lock.  Return
** SQLITE_OK on success and SQLITE_BUSY on a failure.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqlite3OsWriteLock(OsFile *id){
  int rc;
  if( id->locked<0 ){
    rc = SQLITE_OK;
  }else{
    int res;
    int cnt = 100;
    while( cnt-->0 && (res = LockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0))==0 ){
      Sleep(1);
    }

    if( res ){
      if( id->locked>0 ){
        if( isNT() ){
          UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
        }else{
          res = UnlockFile(id->h, FIRST_LOCKBYTE + id->locked, 0, 1, 0);
        }
      }
      if( res ){
        res = LockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
      }else{
        res = 0;
      }
      UnlockFile(id->h, FIRST_LOCKBYTE, 0, 1, 0);
    }
    if( res ){
      id->locked = -1;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
  return rc;
}

/*
** Unlock the given file descriptor.  If the file descriptor was
** not previously locked, then this routine is a no-op.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqlite3OsUnlock(OsFile *id){
  int rc;
  if( id->locked==0 ){
    rc = SQLITE_OK;
  }else if( isNT() || id->locked<0 ){
    UnlockFile(id->h, FIRST_LOCKBYTE+1, 0, N_LOCKBYTE, 0);
    rc = SQLITE_OK;
    id->locked = 0;
  }else{
    UnlockFile(id->h, FIRST_LOCKBYTE+id->locked, 0, 1, 0);
    rc = SQLITE_OK;
    id->locked = 0;
  }
  return rc;



}

/*
** Get information to seed the random number generator.  The seed
** is written into the buffer zBuf[256].  The calling function must
** supply a sufficiently large buffer.
*/

#include "os_common.h"

/*
** Delete the named file
*/
int sqlite3OsDelete(const char *zFilename){
  DeleteFile(zFilename);
  TRACE2("DELETE \"%s\"\n", zFilename);
  return SQLITE_OK;
}

/*
** Return TRUE if the named file exists.
*/
int sqlite3OsFileExists(const char *zFilename){
................................................................................
      return SQLITE_CANTOPEN;
    }
    *pReadonly = 1;
  }else{
    *pReadonly = 0;
  }
  id->h = h;
  id->locktype = NO_LOCK;
  OpenCounter(+1);
  TRACE3("OPEN R/W %d \"%s\"\n", h, zFilename);
  return SQLITE_OK;
}


/*
** Attempt to open a new file for exclusive access by this process.
** The file will be opened for both reading and writing.  To avoid
................................................................................
     fileflags,
     NULL
  );
  if( h==INVALID_HANDLE_VALUE ){
    return SQLITE_CANTOPEN;
  }
  id->h = h;
  id->locktype = NO_LOCK;
  OpenCounter(+1);
  TRACE3("OPEN EX %d \"%s\"\n", h, zFilename);
  return SQLITE_OK;
}

/*
** Attempt to open a new file for read-only access.
**
** On success, write the file handle into *id and return SQLITE_OK.
................................................................................
     FILE_ATTRIBUTE_NORMAL | FILE_FLAG_RANDOM_ACCESS,
     NULL
  );
  if( h==INVALID_HANDLE_VALUE ){
    return SQLITE_CANTOPEN;
  }
  id->h = h;
  id->locktype = NO_LOCK;
  OpenCounter(+1);
  TRACE3("OPEN RO %d \"%s\"\n", h, zFilename);
  return SQLITE_OK;
}

/*
** Attempt to open a file descriptor for the directory that contains a
** file.  This file descriptor can be used to fsync() the directory
** in order to make sure the creation of a new file is actually written
................................................................................
    sqlite3Randomness(15, &zBuf[j]);
    for(i=0; i<15; i++, j++){
      zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
    }
    zBuf[j] = 0;
    if( !sqlite3OsFileExists(zBuf) ) break;
  }
  TRACE2("TEMP FILENAME: %s\n", zBuf);
  return SQLITE_OK; 
}

/*
** Close a file.
*/
int sqlite3OsClose(OsFile *id){
................................................................................
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
int sqlite3OsRead(OsFile *id, void *pBuf, int amt){
  DWORD got;
  SimulateIOError(SQLITE_IOERR);
  TRACE2("READ %d\n", id->h);
  if( !ReadFile(id->h, pBuf, amt, &got, 0) ){
    got = 0;
  }
  if( got==(DWORD)amt ){
    return SQLITE_OK;
  }else{
    return SQLITE_IOERR;
................................................................................
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
int sqlite3OsWrite(OsFile *id, const void *pBuf, int amt){
  int rc;
  DWORD wrote;
  SimulateIOError(SQLITE_IOERR);
  TRACE2("WRITE %d\n", id->h);
  while( amt>0 && (rc = WriteFile(id->h, pBuf, amt, &wrote, 0))!=0 && wrote>0 ){
    amt -= wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  if( !rc || amt>(int)wrote ){
    return SQLITE_FULL;
  }
................................................................................
*/
int sqlite3OsSeek(OsFile *id, off_t offset){
  LONG upperBits = offset>>32;
  LONG lowerBits = offset & 0xffffffff;
  DWORD rc;
  SEEK(offset/1024 + 1);
  rc = SetFilePointer(id->h, lowerBits, &upperBits, FILE_BEGIN);
  TRACE3("SEEK %d %lld\n", id->h, offset);
  return SQLITE_OK;
}

/*
** Make sure all writes to a particular file are committed to disk.
*/
int sqlite3OsSync(OsFile *id){
  TRACE2("SYNC %d\n", id->h);
  if( FlushFileBuffers(id->h) ){
    return SQLITE_OK;
  }else{
    return SQLITE_IOERR;
  }
}

/*
** Truncate an open file to a specified size
*/
int sqlite3OsTruncate(OsFile *id, off_t nByte){
  LONG upperBits = nByte>>32;
  TRACE3("TRUNCATE %d %lld\n", id->h, nByte);
  SimulateIOError(SQLITE_IOERR);
  SetFilePointer(id->h, nByte, &upperBits, FILE_BEGIN);
  SetEndOfFile(id->h);
  return SQLITE_OK;
}

/*
................................................................................
  DWORD upperBits, lowerBits;
  SimulateIOError(SQLITE_IOERR);
  lowerBits = GetFileSize(id->h, &upperBits);
  *pSize = (((off_t)upperBits)<<32) + lowerBits;
  return SQLITE_OK;
}























/*
** Windows file locking notes:
**
** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
** those functions are not available.  So we use only LockFile() and
** UnlockFile().
**
** LockFile() prevents not just writing but also reading by other processes.
** (This is a design error on the part of Windows, but there is nothing
** we can do about that.)  So the region used for locking is at the
** end of the file where it is unlikely to ever interfere with an
** actual read attempt.
**
** A SHARED_LOCK is obtained by locking a single randomly-chosen 
** byte out of a specific range of bytes. The lock byte is obtained at 
** random so two separate readers can probably access the file at the 
** same time, unless they are unlucky and choose the same lock byte.
** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
** There can only be one writer.  A RESERVED_LOCK is obtained by locking
** a single byte of the file that is designated as the reserved lock byte.
** A PENDING_LOCK is obtained by locking a designated byte different from
** the RESERVED_LOCK byte.






**
** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
** which means we can use reader/writer locks.  When reader/writer locks
** are used, the lock is placed on the same range of bytes that is used
** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
** will support two or more Win95 readers or two or more WinNT readers.
** But a single Win95 reader will lock out all WinNT readers and a single
** WinNT reader will lock out all other Win95 readers.
**
** The following #defines specify the range of bytes used for locking.
** SHARED_SIZE is the number of bytes available in the pool from which
** a random byte is selected for a shared lock.  The pool of bytes for
** shared locks begins at SHARED_FIRST.  

*/
#define SHARED_SIZE       10238
#define SHARED_FIRST      (0xffffffff - SHARED_SIZE + 1)
#define RESERVED_BYTE     (SHARED_FIRST - 1)
#define PENDING_BYTE      (RESERVED_BYTE - 1)


/*
** Return true (non-zero) if we are running under WinNT, Win2K or WinXP.
** Return false (zero) for Win95, Win98, or WinME.
**
** Here is an interesting observation:  Win95, Win98, and WinME lack
** the LockFileEx() API.  But we can still statically link against that
** API as long as we don't call it win running Win95/98/ME.  A call to
** this routine is used to determine if the host is Win95/98/ME or
** WinNT/2K/XP so that we will know whether or not we can safely call
** the LockFileEx() API.
*/
static int isNT(void){
  static int osType = 0;   /* 0=unknown 1=win95 2=winNT */
  if( osType==0 ){
    OSVERSIONINFO sInfo;
    sInfo.dwOSVersionInfoSize = sizeof(sInfo);
    GetVersionEx(&sInfo);
    osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
  }
  return osType==2;
}

/*
** Acquire a reader lock on the range of bytes from iByte...iByte+nByte-1.
** Different API routines are called depending on whether or not this
** is Win95 or WinNT.
*/
static int getReadLock(HANDLE h, unsigned int iByte, unsigned int nByte){
  int res;
  if( isNT() ){
    OVERLAPPED ovlp;
    ovlp.Offset = iByte;
    ovlp.OffsetHigh = 0;
    ovlp.hEvent = 0;
    res = LockFileEx(h, LOCKFILE_FAIL_IMMEDIATELY, 0, nByte, 0, &ovlp);
  }else{
    res = LockFile(h, iByte, 0, nByte, 0);
  }
  return res;
}

/*
** Undo a readlock
*/
static int unlockReadLock(OsFile *id){
  int res;
  if( isNT() ){
    res = UnlockFile(id->h, SHARED_FIRST, 0, SHARED_SIZE, 0);
  }else{
    res = UnlockFile(id->h, SHARED_FIRST + id->sharedLockByte, 0, 1, 0);
  }
  return res;
}

/*




** Acquire a lock of the given type on the specified file.  If an
** appropriate lock already exists, this routine is a no-op.  Return
** SQLITE_OK on success and SQLITE_BUSY if another thread is already


** holding a conflicting lock.
*/
int sqlite3OsLock(OsFile *id, int locktype){

  int rc = SQLITE_OK;    /* Return code from subroutines */
  int res = 1;           /* Result of a windows lock call */

  TRACE4("LOCK %d %d was %d\n", id->h, locktype, id->locktype);

  /* If there is already a lock of this type or more restrictive on the
  ** OsFile, do nothing. Don't use the end_lock: exit path, as
  ** sqlite3OsEnterMutex() hasn't been called yet.
  */
  if( id->locktype>=locktype ){
    return SQLITE_OK;
  }

  /* Lock the PENDING_LOCK byte if we need to acquire a PENDING lock or
  ** a SHARED lock.  If we are acquiring a SHARED lock, the acquisition of
  ** the PENDING_LOCK byte is temporary.
  */
  if( id->locktype==NO_LOCK || locktype==PENDING_LOCK ){
    int cnt = 4;
    while( cnt-->0 && (res = LockFile(id->h, PENDING_BYTE, 0, 1, 0))==0 ){
      /* Try 4 times to get the pending lock.  The pending lock might be
      ** held by another reader process who will release it momentarily.
      */
      Sleep(1);
    }
  }

  /* Acquire a shared lock
  */
  if( locktype>=SHARED_LOCK && id->locktype<SHARED_LOCK && res ){
    if( isNT() ){
      res = getReadLock(id->h, SHARED_FIRST, SHARED_SIZE);
    }else{
      int lk;


      sqlite3Randomness(sizeof(lk), &lk);
      id->sharedLockByte = (lk & 0x7fffffff)%(SHARED_SIZE - 1);


      res = LockFile(id->h, SHARED_FIRST+id->sharedLockByte, 0, 1, 0);
    }
    if( locktype<PENDING_LOCK ){
      UnlockFile(id->h, PENDING_BYTE, 0, 1, 0);
    }
  }

  /* Acquire a RESERVED lock
  */
  if( locktype>=RESERVED_LOCK && id->locktype<RESERVED_LOCK && res ){
    res = getReadLock(id->h, RESERVED_BYTE, 1);
  }

  /* Acquire an EXCLUSIVE lock
  */
  if( locktype==EXCLUSIVE_LOCK ){
    if( id->locktype>=SHARED_LOCK ){
      res = unlockReadLock(id);
    }
    if( res ){








      res = LockFile(id->h, SHARED_FIRST, 0, SHARED_SIZE, 0);
    }else{

      res = 0;
    }

  }

  /* Update the state of the lock has held in the file descriptor then
  ** return the appropriate result code.
  */
  if( res ){
    id->locktype = locktype;
    rc = SQLITE_OK;
  }else{
    TRACE2("LOCK FAILED %d\n", id->h);
    rc = SQLITE_BUSY;
  }

  return rc;
}

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, return
** non-zero, otherwise zero.

*/
int sqlite3OsCheckWriteLock(OsFile *id){
  int rc;
  if( id->locktype>=RESERVED_LOCK ){
    rc = 1;
  }else{





    rc = getReadLock(id->h, RESERVED_BYTE, 1);
    if( rc ){












      UnlockFile(id->h, RESERVED_BYTE, 0, 1, 0);
    }





  }

  return 0;
}

/*
** Unlock the given file descriptor.  If the file descriptor was
** not previously locked, then this routine is a no-op.  If this
** library was compiled with large file support (LFS) but LFS is not
** available on the host, then an SQLITE_NOLFS is returned.
*/
int sqlite3OsUnlock(OsFile *id){
  int rc;
  TRACE3("UNLOCK %d was %d\n", id->h, id->locktype);
  if( id->locktype>=EXCLUSIVE_LOCK ){
    UnlockFile(id->h, SHARED_FIRST, 0, SHARED_SIZE, 0);
  }
  if( id->locktype>=PENDING_LOCK ){
    UnlockFile(id->h, PENDING_BYTE, 0, 1, 0);
  }
  if( id->locktype>=RESERVED_LOCK ){
    UnlockFile(id->h, RESERVED_BYTE, 0, 1, 0);
  }
  if( id->locktype==SHARED_LOCK ){
    unlockReadLock(id);
  }
  id->locktype = NO_LOCK;
  return SQLITE_OK;
}

/*
** Get information to seed the random number generator.  The seed
** is written into the buffer zBuf[256].  The calling function must
** supply a sufficiently large buffer.
*/

** of an open file handle.  It is defined differently for each architecture.
**
** This is the definition for Win32.
*/
typedef struct OsFile OsFile;
struct OsFile {
  HANDLE h;               /* Handle for accessing the file */
  int locked;             /* 0: unlocked, <0: write lock, >0: read lock */

};


#define SQLITE_TEMPNAME_SIZE (MAX_PATH+50)
#define SQLITE_MIN_SLEEP_MS 1


#endif /* _SQLITE_OS_WIN_H_ */

** of an open file handle.  It is defined differently for each architecture.
**
** This is the definition for Win32.
*/
typedef struct OsFile OsFile;
struct OsFile {
  HANDLE h;               /* Handle for accessing the file */
  int locktype;           /* Type of lock currently held on this file */
  int sharedLockByte;     /* Randomly chosen byte used as a shared lock */
};


#define SQLITE_TEMPNAME_SIZE (MAX_PATH+50)
#define SQLITE_MIN_SLEEP_MS 1


#endif /* _SQLITE_OS_WIN_H_ */