I suspect that getting the threads to die will be tricky, and as written the thread holds a reference to the 'primegen' instance (this part can be cured, but it still doesn't ever make the thread exit).
Instead of figuring out how to get this to clean itself up, why not make sure you only make one 'primegen' instance, using one of the various singleton patterns? There may still be something "uncollectable", but at least there will only be one. Jeff
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