Support for multiple objects and making it fast is dwarfed by ... requirement for <i>threads</i> (not those green ones).<p>Now all those regions of code where &quot;we can muck with this object before returning it because we know GC isn&#x27;t running, because we don&#x27;t call any allocation functions that can trigger GC&quot; have to be locked down. (Among other problems to solve, like that a thread can be doing anything when you pause it.)