Re: Thread status constants

Message: 2 Date: Sat, 19 Jul 2014 15:00:17 +1000 From: Kyle Van Berendonck To: "ghc-devs@haskell.org" Subject: Thread status constants Message-ID: Content-Type: text/plain; charset="utf-8"

Hi,

I found these: https://github.com/ghc/ghc/blob/5f3c5384df59717ca8013c5df8d1f65692867825/inc...

They go only 0-14, so there's some long chains of branches and stuff in hot paths that could be cleaned up into single &-masked branches by changing these into a set of flags.

And then I saw these: https://github.com/ghc/ghc/blob/master/libraries/base/GHC/Conc/Sync.lhs#L483

Where does 16 and 17 come from -- I couldn't find them in the header files anywhere?

Kyle

Hi Kyle, I had a look at these constants just recently. About 16 and 17, see here: https://github.com/ghc/ghc/blob/master/rts/PrimOps.cmm#L853 About the others:The block reasons received two updates just recently. Turns out that the eventlog (GHC's post-mortem tracing for threadscope et al.) expects these states to have particular values (those in includes/rts/Constants.h, consider them a fixed ABI for the time being). See here for the story: https://ghc.haskell.org/trac/ghc/ticket/9003 NB: Darn... base still uses GHC-7.8.2 constants. Thanks for the pointer! About your proposal to use bit masks: Did you find some of those hot paths? I believe (believe, unchecked...) that there are not too many places where a complete switch over all possible reasons is done (apart from debug output maybe); the typical use is rather to compare to one single constant than to all. So the performance might not increase too much from optimisations. Again, just a hunch, not verified. If the RTS contains code specialised to the current constants, these places need to be kept symbolic, to avoid future breakage when new states are added. A fix which removes the tight implicit dependency of ghc-events from the constants in includes/rts/Constants.h is pending, btw. / Jost