[racket-dev] errors from `force`

At Mon, 27 Aug 2012 17:36:42 -0400, Sam Tobin-Hochstadt wrote:
> Since I've made the Typed Racket tests run in parallel, there have
> been intermittent errors in DrDr, like this:
> 
>   http://drdr.racket-lang.org/25278/collects/tests/typed-racket/run.rkt
> 
> I'm not sure exactly what could be causing this -- I don't think
> promises should ever fail to `force`.  Might there be something I'm
> doing wrong, or is this a bug in promises?

I've fixed a race in `delay/sync' that I think could cause the error.