Parallel --make (GHC build times on newer MacBook Pros?)

Evan Laforge qdunkan at
Tue Aug 30 02:16:24 CEST 2011

On Mon, Aug 29, 2011 at 1:50 PM, Max Bolingbroke
<batterseapower at> wrote:
> On 27 August 2011 09:00, Evan Laforge <qdunkan at> wrote:
>> Right, that's probably the one I mentioned.  And I think he was trying
>> to parallelize ghc internally, so even compiling one file could
>> parallelize.  That would be cool and all, but seems like a lot of work
>> compared to just parallelizing at the file level, as make would do.
> It was Thomas Schilling, and he wasn't trying to parallelise the
> compilation of a single file. He was just trying to make access to the
> various bits of shared state GHC uses thread safe. This mostly worked
> but caused an unacceptable performance penalty to single-threaded
> compilation.

Interesting, maybe I misremembered?  Or maybe there was some other guy
who was trying to parallelize?

Just out of curiosity, what benefit does a thread-safe ghc provide?  I
know ghc api users have go to some bother to not call re-entrantly...
what neat stuff could we do with a re-entrant ghc?  Could it
eventually lead to an internally parallel ghc or are there deeper
reasons it's hard to parallelize compilation?  That would be really
cool, if possible.  In fact, I don't know of any parallel compilers.

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