SQLite

  int res = 1;           /* Result of a windows lock call */
  int newLocktype;       /* Set pFile->locktype to this value before exiting */
  int gotPendingLock = 0;/* True if we acquired a PENDING lock this time */
  winFile *pFile = (winFile*)id;
  DWORD error = NO_ERROR;

  assert( id!=0 );
  OSTRACE(("LOCK %d %d was %d(%d)\n",
           pFile->h, locktype, pFile->locktype, pFile->sharedLockByte));

  /* 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( pFile->locktype>=locktype ){
    return SQLITE_OK;

       NULL,
       dwCreationDisposition,
       dwFlagsAndAttributes,
       NULL
    );
#endif
  }
  OSTRACE(("OPEN %d %s 0x%lx %s\n", 
           h, zName, dwDesiredAccess, 
           h==INVALID_HANDLE_VALUE ? "failed" : "ok"));
  if( h==INVALID_HANDLE_VALUE ){
    free(zConverted);
    if( flags & SQLITE_OPEN_READWRITE ){
      return winOpen(pVfs, zName, id, 
             ((flags|SQLITE_OPEN_READONLY)&~SQLITE_OPEN_READWRITE), pOutFlags);
    }else{
      return SQLITE_CANTOPEN_BKPT;

  /* Access to the winShmFile object is serialized by the caller */
  assert( sqlite3_mutex_held(pFile->mutex) || pFile->nRef==0 );

  /* Initialize the locking parameters */
  if( lockMask==WIN_SHM_C && lockType!=_SHM_UNLCK ){
    dwFlags = 0;
    OSTRACE(("SHM-LOCK %d requesting blocking lock %s\n", 
             pFile->hFile.h,
             winShmLockString(lockMask)));
  }else{
    dwFlags = LOCKFILE_FAIL_IMMEDIATELY;
    OSTRACE(("SHM-LOCK %d requesting %s %s\n", 
             pFile->hFile.h,
             lockType!=_SHM_UNLCK ? "lock" : "unlock", 
             winShmLockString(lockMask)));
  }
  if( lockType == _SHM_WRLCK ) dwFlags |= LOCKFILE_EXCLUSIVE_LOCK;

  /* Find the first bit in lockMask that is set */
  for(i=0, mask=0x01; mask!=0 && (lockMask&mask)==0; mask <<= 1, i++){}
  assert( mask!=0 );
  memset(&ovlp, 0, sizeof(OVERLAPPED));
  ovlp.Offset = i+WIN_SHM_BASE;

  nBytes = 1;

  /* Extend the locking range for each additional bit that is set */
  mask <<= 1;
  while( mask!=0 && (lockMask & mask)!=0 ){
    nBytes++;
    mask <<= 1;
  }

  /* Verify that all bits set in lockMask are contiguous */
  assert( mask==0 || (lockMask & ~(mask | (mask-1)))==0 );

  /* Release/Acquire the system-level lock */
  if( lockType==_SHM_UNLCK ){
    for(i=0; i<nBytes; i++, ovlp.Offset++){
      rc = UnlockFileEx(pFile->hFile.h, 0, 1, 0, &ovlp);
      if( !rc ) break;
    }







  }else{
    /* release old individual byte locks (if any)
    ** and set new individual byte locks */
    for(i=0; i<nBytes; i++, ovlp.Offset++){
      UnlockFileEx(pFile->hFile.h, 0, 1, 0, &ovlp);




      rc = LockFileEx(pFile->hFile.h, dwFlags, 0, 1, 0, &ovlp);
      if( !rc ) break;
    }
  }
  if( !rc ){
    OSTRACE(("SHM-LOCK %d %s ERROR 0x%08lx\n", 
             pFile->hFile.h,
             lockType==_SHM_UNLCK ? "UnlockFileEx" : "LockFileEx", GetLastError()));
    /* release individual byte locks (if any) */
    ovlp.Offset-=i;
    for(i=0; i<nBytes; i++, ovlp.Offset++){
      UnlockFileEx(pFile->hFile.h, 0, 1, 0, &ovlp);

    }
  }
  rc = (rc!=0) ? SQLITE_OK : SQLITE_BUSY;

  /* Update the global lock state and do debug tracing */
#ifdef SQLITE_DEBUG
  OSTRACE(("SHM-LOCK %d ", pFile->hFile.h));

  u8 allMask;  /* Union of locks held by connections other than "p" */

  /* Access to the winShmFile object is serialized by the caller */
  assert( sqlite3_mutex_held(pFile->mutex) );

  /* don't attempt to unlock anything we don't have locks for */
  if( (unlockMask & (p->exclMask|p->sharedMask)) != unlockMask ){
    OSTRACE(("SHM-LOCK %d unlocking more than we have locked - requested %s - have %s\n",
             pFile->hFile.h,
             winShmLockString(unlockMask),
             winShmLockString(p->exclMask|p->sharedMask)));
    unlockMask &= (p->exclMask|p->sharedMask);
  }

  /* Compute locks held by sibling connections */
  allMask = 0;

** the file must be truncated to zero length or have its header cleared.
*/
static int winShmOpen(
  sqlite3_vfs *pVfs,    /* The VFS */
  const char *zName,    /* Name of the corresponding database file */
  sqlite3_shm **pShm    /* Write the winShm object created here */
){
  struct winShm *p;                  /* The connection to be opened */
  struct winShmFile *pFile = 0;      /* The underlying mmapped file */
  int rc;                            /* Result code */
  struct winShmFile *pNew;           /* Newly allocated pFile */
  int nName;                         /* Size of zName in bytes */
  char zFullpath[MAX_PATH+1];        /* Temp buffer for full file name */

  rc = winFullPathname(pVfs, zName, MAX_PATH, zFullpath);
  if( rc ) return rc;

  /* Allocate space for the new sqlite3_shm object.  Also speculatively
  ** allocate space for a new winShmFile and filename.
  */
  p = sqlite3_malloc( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM;
  memset(p, 0, sizeof(*p));
  nName = sqlite3Strlen30(zFullpath);
  pNew = sqlite3_malloc( sizeof(*pFile) + nName + 15 );
  if( pNew==0 ){
    sqlite3_free(p);
    return SQLITE_NOMEM;
  }
  memset(pNew, 0, sizeof(*pNew));
  pNew->zFilename = (char*)&pNew[1];
  sqlite3_snprintf(nName+12, pNew->zFilename, "%s-wal-index", zFullpath);

  /* Look to see if there is an existing winShmFile that can be used.
  ** If no matching winShmFile currently exists, create a new one.
  */
  winShmEnterMutex();
  for(pFile = winShmFileList; pFile; pFile=pFile->pNext){
    /* TBD need to come up with better match here.  Perhaps
    ** use FILE_ID_BOTH_DIR_INFO Structure.
    */
    if( sqlite3StrICmp(pFile->zFilename, pNew->zFilename)==0 ) break;
  }
  if( pFile ){
    sqlite3_free(pNew);
  }else{
    pFile = pNew;
    pNew = 0;
    pFile->pMMapBuf = NULL;

      goto shm_open_err;
    }
    pFile->mutexBuf = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pFile->mutexBuf==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    rc = winOpen(pVfs,
                 pFile->zFilename,                  /* Name of the file (UTF-8) */
                 (sqlite3_file *)&pFile->hFile, /* Write the SQLite file handle here */
                 SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, /* Open mode flags */
                 0);
    if( SQLITE_OK!=rc ){
      rc = SQLITE_CANTOPEN_BKPT;

  /* Return directly if this is just a lock state query, or if
  ** the connection is already in the desired locking state.
  */
  if( desiredLock==p->lockState
   || (desiredLock==SQLITE_SHM_READ && p->lockState==SQLITE_SHM_READ_FULL)
  ){
    OSTRACE(("SHM-LOCK %d shmid-%d, pid-%d request %s and got %s\n",
             pFile->hFile.h,
             p->id, (int)GetCurrentProcessId(), azLkName[desiredLock], azLkName[p->lockState]));
    if( pGotLock ) *pGotLock = p->lockState;
    return SQLITE_OK;
  }

  OSTRACE(("SHM-LOCK %d shmid-%d, pid-%d request %s->%s\n",
           pFile->hFile.h,
           p->id, (int)GetCurrentProcessId(), azLkName[p->lockState], azLkName[desiredLock]));
  
  if( desiredLock==SQLITE_SHM_RECOVER && !p->hasMutexBuf ){
    assert( sqlite3_mutex_notheld(pFile->mutex) );
    sqlite3_mutex_enter(pFile->mutexBuf);
    p->hasMutexBuf = 1;
  }
  sqlite3_mutex_enter(pFile->mutex);

      if( rc==SQLITE_OK ){
        p->lockState = SQLITE_SHM_RECOVER;
      }
      break;
    }
  }
  sqlite3_mutex_leave(pFile->mutex);
  OSTRACE(("SHM-LOCK %d shmid-%d, pid-%d got %s\n",
           pFile->hFile.h, 
           p->id, (int)GetCurrentProcessId(), azLkName[p->lockState]));
  if( pGotLock ) *pGotLock = p->lockState;
  return rc;
}

#else
# define winShmOpen    0