[Haskell-cafe] Re: Automatic parallelism in Haskell, similar to "make -j4"?

Simon Marlow marlowsd at gmail.com
Wed Nov 19 08:51:55 EST 2008

Bulat Ziganshin wrote:
> Hello Chad,
> Wednesday, November 5, 2008, 6:34:01 AM, you wrote:
>> ghc --make -j4 Foo.hs
> afair, it was implemented and not shown speed improvements. ask Simon

We did get speed improvements, it was the main case study for the initial 
implementation of shared-memory parallelism in GHC.  See


However, due to the way GHC is structured internally (it has some global 
caches updated using unsafePerformIO!) the parallel make implementation was 
quite fragile, and wasn't suitable for incorporating into GHC proper.  It's 
certainly possible, but we need to think carefully about how to make these 
caches multi-thread-safe.


More information about the Haskell-Cafe mailing list