Randomize is not thread-safe. It mutates shared data structures in a memory-unsafe way (no synchronization/locking).
Even with @yglukhoov's suggestion of using []=, you would still need some form of coordination to figure out which parts of the list each thread should assign to, in order to ensure they are non-overlapping. For such use-case, my recommendation would be to use a sharedlist ([https://nim-lang.org/docs/sharedlist.html)](https://nim-lang.org/docs/sharedlist.html\)).
