[Haskell-cafe] concurrency vs. I/O in GHC

Andrew Coppin andrewcoppin at btinternet.com
Thu Oct 28 13:06:14 EDT 2010

On 28/10/2010 09:25 AM, Erik Hesselink wrote:
> On Wed, Oct 27, 2010 at 23:09, Andrew Coppin
> <andrewcoppin at btinternet.com>  wrote:
>> GHC has a _parallel_ GC implementation, meaning that the GC event runs in
>> parallel on several cores. But it does not (yet) have _concurrent_ GC,
>> meaning that a GC event can happen at the same time as Haskell threads are
>> running. (Basically, which Haskell code running, the references between
>> objects could change while the GC engine is trying to analyse them, which
>> would be Bad.) I understand that the developers are actively working on
>> fixing this, since it can sometimes have a significant effect on the
>> performance of multicore programs...
> I thought that young generations could be GC'ed while other threads
> were running, while collecting the old generation required
> synchronizing all threads. This seems to be what is shown on
> http://hackage.haskell.org/trac/ghc/blog/new-gc-preview as well.

"I expect it to land in GHC HEAD in a few months time, and it should be 
in the autumn 2011 major release of GHC."

In other words, this isn't how GHC works now, it's how some future 
version will work.

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