The Lua call stack and C call stack are two separate things. The Lua VM
does not use longjmp() to implement coroutines [a][d].
Really? I can’t look at the code right now, but I’d always assumed that Lua always used longjmp (as per the OPs point). How can it do otherwise? At any time a Lua state can have any number of intermixed C and Lua frames, and while you are correct in that they dont share the same stack, Lua needs to resume by longjmp to make sure the C stack corresponds to the Lua coroutine state. While I can see that Lua *might* optimize out this condition if it knows there are NO C calls on either coroutine stack, I’m not sure that it does that?
—Tim
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