#include <db_cxx.h> DbEnv::close(u_int32_t flags);
         The DbEnv::close() method closes the
         Berkeley DB environment, freeing any allocated resources and
         closing all database handles opened with this environment handle,
         as well as closing any underlying subsystems.
    
        When you call the DbEnv::close() method,
        all open Db handles and 
        Dbc handles are closed
        automatically by this function. And, when you close a database
        handle, all cursors opened with it are closed automatically.
    
       In multiple threads of control, each thread of control opens a
       database environment and the database handles within it. When you
       close each database handle using the
       DbEnv::close() method, by default, the
       database is not synchronized and is similar to calling the
       Db::close(DB_NOSYNC) method. This is to
       avoid unncessary database synchronization when there are multiple
       environment handles open.  To ensure all open database handles are
       synchronized when you close the last environment handle, set the
       flag parameter value of the DbEnv::close()
       method to DB_FORCESYNC.  This is similar to calling the
       Db::close(0) method to close each database
       handle. 
    
If a database close operation fails, the method returns a non-zero error value for the first instance of such an error, and continues to close the rest of the database and environment handles.
The DbEnv handle should not be closed while any other handle that refers to it is not yet closed; for example, database environment handles must not be closed while transactions in the environment have not yet been committed or aborted. Specifically, this includes the DbTxn, DbLogc and DbMpoolFile handles.
         Where the environment was initialized with the 
         DB_INIT_LOCK  flag,
         calling DbEnv::close() does not release any locks still held by the
         closing process, providing functionality for long-lived locks.
         Processes that want to have all their locks released can do so by
         issuing the appropriate DbEnv::lock_vec()  call.
    
         Where the environment was initialized with the 
         DB_INIT_MPOOL flag,
         calling DbEnv::close() implies calls to 
         DbMpoolFile::close()  for any
         remaining open files in the memory pool that were returned to this
         process by calls to DbMpoolFile::open().  It does
         not imply a call to DbMpoolFile::sync()  for those
         files.
    
         Where the environment was initialized with the 
         DB_INIT_TXN  
         flag, calling DbEnv::close() aborts any
         unresolved transactions.  Applications should not depend on this
         behavior for transactions involving Berkeley DB databases; all
         such transactions should be explicitly resolved.  The problem with
         depending on this semantic is that aborting an unresolved
         transaction involving database operations requires a database
         handle.  Because the database handles should have been closed
         before calling DbEnv::close(), it will not
         be possible to abort the transaction, and recovery will have to be
         run on the Berkeley DB environment before further operations are
         done.
    
         Where log cursors were created using the 
         DbEnv::log_cursor()  method,
         calling DbEnv::close() does not imply
         closing those cursors.
    
         In multithreaded applications, only a single thread may call the
         DbEnv::close() method.
     
         After DbEnv::close() has been called,
         regardless of its return, the Berkeley DB environment handle may
         not be accessed again.
    
         The DbEnv::close() 
            
            
                method either returns a non-zero error value or throws an
                exception that encapsulates a non-zero error value on
                failure, and returns 0 on success.