[immibis]

AFAIK a group of instructions is only non-protected if one of the instructions does I/O. Explicit I/O - page faults don't count.

[kfrane]

If I understand that correctly, it would mean that running a function like this on two threads f(1) and f(2) would produce a list of 1 and 2 without interleaving.

  def f(x):
      for _ in range(N):
          l.append(x)

I've tried it out and they start interleaving when N is set to 1000000.