Wal *pWal,                      /* Wal to close */
  sqlite3_file *pFd,              /* Database file */
  int sync_flags,                 /* Flags to pass to OsSync() (or 0) */
  u8 *zBuf                        /* Buffer of at least page-size bytes */
){
  int rc = SQLITE_OK;
  if( pWal ){



















    pWal->pVfs->xShmClose(pWal->pWIndex);
    sqlite3OsClose(pWal->pFd);








    sqlite3_free(pWal);
  }
  return rc;
}

/*
** Try to read the wal-index header. Attempt to verify the header
................................................................................
** been overwritten by another writer, SQLITE_BUSY is returned.
*/
int sqlite3WalWriteLock(Wal *pWal, int op){
  int rc;
  if( op ){
    assert( pWal->lockState == SQLITE_SHM_READ );
    rc = walSetLock(pWal, SQLITE_SHM_WRITE);

















  }else if( pWal->lockState==SQLITE_SHM_WRITE ){
    rc = walSetLock(pWal, SQLITE_SHM_READ);
  }
  return rc;
}

/*

  Wal *pWal,                      /* Wal to close */
  sqlite3_file *pFd,              /* Database file */
  int sync_flags,                 /* Flags to pass to OsSync() (or 0) */
  u8 *zBuf                        /* Buffer of at least page-size bytes */
){
  int rc = SQLITE_OK;
  if( pWal ){
    int isDelete = 0;             /* True to unlink wal and wal-index files */

    /* If an EXCLUSIVE lock can be obtained on the database file (using the
    ** ordinary, rollback-mode locking methods, this guarantees that the
    ** connection associated with this log file is the only connection to
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
    rc = sqlite3OsLock(pFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      rc = walCheckpoint(pWal, pFd, sync_flags, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
      walIndexUnmap(pWal);
    }

    pWal->pVfs->xShmClose(pWal->pWIndex);
    sqlite3OsClose(pWal->pFd);
    if( isDelete ){
      int nWal;
      char *zWal = &((char *)pWal->pFd)[pWal->pVfs->szOsFile];
      sqlite3OsDelete(pWal->pVfs, zWal, 0);
      nWal = sqlite3Strlen30(zWal);
      memcpy(&zWal[nWal], "-index", 7);
      pWal->pVfs->xShmDelete(pWal->pVfs, zWal);
    }
    sqlite3_free(pWal);
  }
  return rc;
}

/*
** Try to read the wal-index header. Attempt to verify the header
................................................................................
** been overwritten by another writer, SQLITE_BUSY is returned.
*/
int sqlite3WalWriteLock(Wal *pWal, int op){
  int rc;
  if( op ){
    assert( pWal->lockState == SQLITE_SHM_READ );
    rc = walSetLock(pWal, SQLITE_SHM_WRITE);

    /* If this connection is not reading the most recent database snapshot,
    ** it is not possible to write to the database. In this case release
    ** the write locks and return SQLITE_BUSY.
    */
    if( rc==SQLITE_OK ){
      rc = walIndexMap(pWal, -1);
      if( rc==SQLITE_OK
       && memcmp(&pWal->hdr, pWal->pWiData, sizeof(WalIndexHdr))
      ){
        rc = SQLITE_BUSY;
      }
      walIndexUnmap(pWal);
      if( rc!=SQLITE_OK ){
        walSetLock(pWal, SQLITE_SHM_READ);
      }
    }
  }else if( pWal->lockState==SQLITE_SHM_WRITE ){
    rc = walSetLock(pWal, SQLITE_SHM_READ);
  }
  return rc;
}

/*