[racket-dev] What can cause "Interactions disabled"?

I have a long-running random simulation that spits out debug messages. I 
extrapolated that it would take 20 hours to get 5,000,000 samples, and 
let it run for a day. Here's what I saw when I returned:


Welcome to DrRacket, version 5.90.0.9--2013-10-04(876995d5/d) [3m].
Language: typed/racket [custom]; memory limit: 1024 MB.
starting...
sample-search-tree returned failure
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
i = 100
refinement-sample-point returned #f
refinement-sample-point returned #f

[...]

refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
i = 2605500
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f
refinement-sample-point returned #f

Interactions disabled
|

       560157:0        720.77MB


Fear my ASCII art status bar.

"720.77MB" is what I got after clicking the GC indicator. (Before, it 
was about 300MB.) There were no command-line messages from DrRacket.

I don't think this is an out-of-memory problem. DrRacket has been good 
about asking for more during other simulations, my limit is set to 
1024MB, and I really doubt I'm allocating a 304MB temporary object.

I wrote a small program to print 600000 debug messages, thinking it was 
a limit on the number of lines in the REPL, and it ran to completion.

For full disclosure: I paused and restarted DrRacket from the command 
line (fg; ctrl-z; bg) a few times while the simulation was running, so I 
could use my laptop unplugged without draining the battery.

Besides running out of memory, what else could cause a program to halt 
with "Interactions disabled", and how can I avoid it?

Neil ⊥