thread blocked indefinitely in an MVar operation (HP 2013 ghc 7.6.3 on mac) with current monad par via criterion

[cartazio]

This is the issue i reported in Criterion haskell/criterion#28 and mistakenly in an older closed monad-par ticket.

Likely hit via Criterion calling the following function in Statistics that is the only use of Monad par in Criterion or Statistics haskell/criterion#28

[cartazio]

I'm sorry, I mean the only use site of monad par in Criterion and Statistics is https://github.com/bos/statistics/blob/master/Statistics/Resampling/Bootstrap.hs#L87-L90

so it seems very very likely its a monad par problem

[cartazio]

I'm happy to help someone else narrow this bug down, but I'm not familiar with much of GHC concurrency stuff (as yet), so help would be appreciated

[gatoatigrado]

Hi, I'm seeing possibly-related issues with ParIO; is there any way to switch that to the Trace scheduler as well? I tried substituting Direct with Trace (in the latest Github checkout) and that doesn't seem to work [ http://pastebin.com/ww7KZSS9 -- sorry I can't interpret the error ].

Sorry I haven't reduced it to a minimal use case, but my use of monad-par is just to do a parallel map (essentially, mapM get =<< mapM (spawn . liftIO . worker_task) inputs). I'm using read-only functionality on Data.HashTable objects (IO flavor, hashtables package), so I don't see how that'd be not thread-safe.

Thanks in advance for your input.

[cartazio]

@gatoatigrado have you tried using the newest version on hackage? http://hackage.haskell.org/package/monad-par-0.3.4.3

[simonmar]

I've just uploaded 0.3.4.4 which switches the ParIO monad over to the Trace scheduler too.

[gatoatigrado]

Hi Dr. Marlow, That seems to fix the problem for me. Thank you very much!! Sorry I couldn't / can't share example codes (I was doing a proof-of-concept project at my work).