My guess is that your problem may be related to the number of threads you're using.

I can't tell from your program how many threads you are starting up (it looks like it's dependent on a data file), but I do know that, in situations where I've tried to create hundreds of threads, I often will get the same Out of memory! error.

The reason that it's misleading is that it doesn't just depend on the number of threads, it also depends on the context, what each thread is doing, and at which time.  That's why it can easily look like a separate issue.

My recommendation would be to first try limiting the number of threads (unless it is already quite small), and see if the behavior changes at all.  If that doesn't do it, even for a small quantity (eg. less than 20), then perhaps your problem really does lie elsewhere.