[Haskell-cafe] Re: Real-time garbage collection for Haskell

[Malcolm Wallace]

> Both concurrent GC and incremental GC tend to add overheads to the  
> mutator, because they need a read barrier.  There was an incremental  
> GC for GHC once [1], taking advantage of the built-in read barrier  
> that we have whereby most closures are "entered"

Was there a specific reason why that GC implementation chose to use a  
read barrier rather than a write barrier?  I would have thought that  
in general, a write barrier is cheaper to implement.  Doesn't ghc  
update fewer thunks than it enters?

Regards,
     Malcolm