#include <db.h> int DB_ENV->mutex_lock(DB_ENV *dbenv, db_mutex_t mutex);
        The DB_ENV->mutex_lock() method locks the mutex allocated by 
        DB_ENV->mutex_alloc().  The
         thread of control calling DB_ENV->mutex_lock() will block until the
         lock is available.
    
         The DB_ENV->mutex_lock() 
            
                  method returns a non-zero error value on failure and 0 on success.
            
            
        
    
The mutex parameter is a mutex previously allocated by DB_ENV->mutex_alloc().
                         The DB_ENV->mutex_lock() 
            
                 method may fail and return one of the following non-zero errors: