Error reporting from map function

Hi,

Apologies for yet another question from me, but here goes!

I've written a map task that will on occasion not compute the correct  
result. This can easily be detected, at which point I'd like the map  
task to report the error and terminate the entire map/reduce job. Does  
anyone know of a way I can do this?

I've been looking around the archives and the api, and the only thing  
that comes close is the reporter class, but I can't I think that only  
reports stuff and doesn't actually allow control of the job?

Any help much appreciated as ever,

Cheers,
Ollie