[Haskell-cafe] Re: Stream processors
simons at cryp.to
Thu Oct 21 17:19:32 EDT 2004
Ben Rudiak-Gould writes:
> bar :: StreamProc ctx a -> IO (a,a)
> bar sp = do
> ctx <- start sp
> (ptr1,n1) <- ...
> (ptr2,n2) <- ...
> ctx1 <- feed sp ctx (ptr1,n1)
> ctx2 <- feed sp ctx (ptr2,n2)
> val1 <- commit sp ctx1
> val2 <- commit sp ctx2
> return (val1,val2)
Ah! Now I understand what you meant with single-threaded
versus multi-threaded use of the stream processor.
Well, in the general case the result would be undefined,
because not every stream processor allows a context to be
re-used. The SHA1 implementation I use, for example, has a
..., so both val1 and val2 would be the hash of the
concatenation of both buffers. Which is not what you'd
expect. A different implementation, on the other hand, might
give you the hash of the first and second block
Hmmm. So I have those options:
(1) If you want to use _any_ stream processor, you must use
it single-threadedly. If you use it multi-threadedly,
you have to know what you're doing.
(2) Have distinct types (or classes) for stream processors
that allow the context to be re-used and for those
which do not.
So far, I've implicitly used (1).
More information about the Haskell-Cafe