- Does the compiler use escape analysis to determine that the `cursor` variable needs to be heap allocated? If not, how does it know that the worker threads won't outlive the stack frame that owns `cursor`? If so, when does the allocation get freed? And does implicit heap allocation conflict with the goal of being as fast as C?

- How does the compiler know that the `lock` block is the only code that touches `cursor`? Does it still work if the `lock` block is in a subroutine? Does that require whole-program analysis? If two different `lock` blocks touch the same variable, are they implicitly a single `lock`?