Re: [Haskell-cafe] multi-thread and lazy evaluation

This seems like a bug in GHC. But it has nothing to do with MVars.  I've narrowed this down and filed a bug report here: http://hackage.haskell.org/trac/ghc/ticket/7528 Timothy ---------- Původní zpráva ---------- Od: Yuras Shumovich <shumovichy@gmail.com> Datum: 24. 12. 2012 Předmět: Re: [Haskell-cafe] multi-thread and lazy evaluation "On Mon, 2012-12-24 at 16:16 +0100, timothyhobbs@seznam.cz wrote:

The real question is, does this mean that GHC is stopping the world every time it puts an MVar?

No, GHC rts only locks the MVar itself. See here: http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358 (http://hackage.haskell.org/trac/ghc/browser/rts/PrimOps.cmm#L1358) Yuras"