DB_File WTF (was GDBM_File WTF?)

[Andy Armstrong]

On 8 Apr 2007, at 18:39, Andy Armstrong wrote:
> Did you miss my post? It's not safe to modify the tied hash during  
> iteration. That's a limitation the Perl wrapper inherits from the  
> underlying library.

Specifically:

>
> Mustn't like deleting while it's got a cursor active.
>
> From:
>   http://ccrma.stanford.edu/planetccrma/man/man3/gdbm.3.html
>
>     File `visiting' is based on a `hash table'. gdbm_delete re- 
> arranges
>     the hash table to make sure that any collisions in the table do  
> not
>     leave some item `un-findable'. The original key order is NOT  
> guaran-
>     teed to remain unchanged in ALL instances. It is possible that  
> some
>     key will not be visited if a loop like the following is executed:
>
>       key = gdbm_firstkey ( dbf );
>       while ( key.dptr ) {
>          nextkey = gdbm_nextkey ( dbf, key );
>          if ( some condition ) {
>             gdbm_delete ( dbf, key );
>             free ( key.dptr );
>          }
>          key = nextkey;
>       }
>
> Seems a bit surprising that it misses /all/ of them - but I guess  
> it's not a good idea to iterate and modify at the same time.
>


-- 
Andy Armstrong, hexten.net