Re: setnumcapabilities001 failure

I see, but the compiler has no business caching things across requestSync(), which can in principle change anything: even if the compiler could see all the code, it would find a pthread_condwait() in there. Anyway I've found the problem - it was caused by a subsequent GC overwriting the values of

Re: setnumcapabilities001 failure

Right, it is compiler effects at this boundary that I'm worried about, values that are not read from memory after the changes have been made, not memory effects or data races. On Fri, Oct 28, 2016 at 3:02 AM, Simon Marlow wrote: > Hi Ryan, I don't think that's the issue.

Re: setnumcapabilities001 failure

Hi Ryan, I don't think that's the issue. Those variables can only be modified in setNumCapabilities, which acquires *all* the capabilities before it makes any changes. There should be no other threads running RTS code(*) while we change the number of capabilities. In particular we shouldn't be

Re: setnumcapabilities001 failure

Briefly looking at the code it seems like several global variables involved should be volatile: n_capabilities, enabled_capabilities, and capabilities. Perhaps in a loop like in scheduleDoGC the compiler moves the reads of n_capabilites or capabilites outside the loop. A failed requestSync in

Re: setnumcapabilities001 failure

Simon Marlow writes: > I haven't been able to reproduce the failure yet. :( > Indeed I've also not seen it in my own local builds. It's quite an fragile failure. Cheers, - Ben signature.asc Description: PGP signature ___

Re: setnumcapabilities001 failure

Simon Marlow writes: > How many cores does the builder machine have? (this should make it easier > for me to repro) > It looks like 8. Cheers, - Ben signature.asc Description: PGP signature ___ ghc-devs mailing list

setnumcapabilities001 failure

Hi Simon, It seems that setnumcapabilities001 still occassionally fails, although this time by a different mode: https://phabricator.haskell.org/harbormaster/build/14485/?l=100 Cheers, - Ben signature.asc Description: PGP signature ___ ghc-devs