ghc 7.10.1 hard lock on exit with shake, OS X 10.10

[Evan Laforge]

On Tue, Jun 2, 2015 at 7:20 PM, Carter Schonwald
<carter.schonwald at gmail.com> wrote:
> could you share a minimal program that reproduces the problem?

That's the thing, it's a thousand line shakefile that builds a 100k
line program, and it's happening only rarely now.  Since it happens so
rarely it seems really difficult to prune away bits to see if it still
happens.  I suppose since the building is all just running commands,
the source it's building doesn't matter, but since it's a build, it
runs a different sequence of commands every time.  I suppose I could
"stub out" the program by replacing ghc with a shell script that
sleeps and touches the output files, but it feels like I could spend
days on it because there are tons of little details.

I'm pretty sure it's related to the threaded runtime, because it
doesn't happen without -threaded.  I could try with -debug, but that
probably turns off -threaded too, so no more problem.  Shake is
heavily threaded and nondeterministic.  I haven't seen other shake
users report it though.