Re: [Haskell-cafe] When are MVars better than STM?

Yuras, On Sun, 2016-01-24 at 17:46 +1100, Thomas Koster wrote:

2. When given two capabilities (+RTS -N2), MVars are suddenly an order of magnitude slower than with just one capability. Why?

On 25 January 2016 at 02:09, Yuras Shumovich wrote:

One possible explanation is closure locking which is not performed when there is only one capability. In my quick measurements it gives 40% speedup: https://ghc.haskell.org/trac/ghc/ticket/693#comment:9

This makes sense. After all, why bother with locks and barriers when the process is single-threaded anyway? Thanks for your response. -- Thomas Koster