[racket] can custodian-shutdown-all interrupt an #:atomic callback?

At Fri, 9 Sep 2011 17:39:38 -0700, John Clements wrote:
> It looks to me as though when a custodian-shutdown-all occurs, the
> custodian actions associated using scheme_add_managed() can be
> triggered while another thread is in the middle of a callback to an
> FFI-generated callback that includes the #:atomic declaration. Is
> this true? If true, is it only true for some certain set of
> (avoidable) circumstances?

The possibility that comes to mind is a custodian shutdown triggered by
a memory-use limit. It looks easy and sensible to disallow that.

Could that be what you saw, or should I look for other possibilities?