Re: Semantics of MVars and IORefs?

Hi Iavor and Ryan, One ticket on memory model issues is #12469. At openSUSE we see several build failures only now because we recently switched to parallel Cabal builds. A compiled Cabal Setup that is called with -j<n> sometimes segfaults on PowerPC. Actually, if I try building package OpenGL locally on my PowerMac Setup -j<n> almost always fails with a segfault if n is the number of cores or higher. See also #12537. When building on Open(SUSE) Build Service the build fails only sometimes. We build all of LTS Haskell and a random selection of around 40 packages fail, most of them with segfaults in Setup but some with GHC panics. #12469 has examples. Peter

On 21.10.2016, at 19:56, Ryan Yates wrote:

Hi Iavor,

You might be interested in what Edward has written about this:

http://blog.ezyang.com/2014/01/so-you-want-to-add-a-new-concurrency-primitiv...

I would say when we do have a memory model for GHC the program you gave will almost certainly be correct. MVar operations should be full synchronization operations. There are some bugs on relaxed systems with initialization that I think are being addressed. I can't find the tickets at the moment.

Ryan