[Haskell-cafe] Re: Hugs vs GHC (again)was: Re: Somerandomnewbiequestions

Duncan Coutts duncan.coutts at worc.ox.ac.uk
Mon Jan 17 09:04:46 EST 2005

On Mon, 2005-01-17 at 13:44 -0800, Ben Rudiak-Gould wrote:
> John Meacham wrote:
>  >Actually, If I were writing new haskell libraries, I would use mmap
>  >whenever I could for accessing files. not only does it make the file
>  >pointer problem go away, but it can be drastically more efficient.
> I'm not sure this is a good idea, because GHC really needs non-blocking 
> I/O to support its thread model, and memory-mapped I/O always blocks. In 
> fact this is a problem even if we only memory-map files at the 
> programmer's request.

Indeed, a new IO system that could transparently take advantage of the
system's native asynchronous IO features might be a good fit to GHC's
thread model.

Note that just using lots of system threads and blocking IO is usually
not as efficient as single(/few) threaded multiplexed IO like GHC uses
currently. Some OSs that do not have kernel native async IO implement
the POSIX async IO API using OS threads and tend to get poor performance
and few users.


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