Idea: limited life-before-main for statics runtime initialization

language design
2

(no expressed opinion on the proposed feature)

(generally I prefer OnceCell to lazy_static nowadays)

The general solution to the problem for libs where using a global matters for performance is to either

  • have the caller initialize a Ctx and pass references to that, or
  • have the caller create a zero-sized InitToken that proves they've called a init() -> InitToken, which is truly zero-cost to pass as an argument, or
  • if it really needs to be global data, have an unsafe requirement to call some initialization function

It's interesting that you're already using an InitToken to prove that the global cell has been initialized and won't be written again. It should be possible to use unsafe to convince the optimizer to do a non-atomic read (and optimize as such). It's clearly a bug that this currently doesn't happen (and likely due to underutilization of noalias, which I believe is still enabled (finally)).

I'd even argue that a Relaxed ordering allows the desired optimization. I don't think life-before-main is required to get the result you're looking for in the linked urlo thread.

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