If you ever want to allow parking a fiber with a native method on the stack

[Florian Weimer]

* Stephane Epardaud:

> I've done this before in a Scheme VM that ran fibers-like threads. The
> trick was to mark native methods that are reentrant (call back into
> non-native code) so that they get executed in an alternate stack when
> called by a fiber. The fiber would then wait for the native method to
> either return or reenter and continue from there, in both cases with its
> own stack clean. If that native call reentered you can mark the fiber
> stack to remember it, and proceed. When you copy the fiber stack you
> will copy the markers too and leave the delegate native stacks alone.
> And when the fiber needs to pop back to the reentring native call you do
> the same dance in reverse.

That was before wide use of TLS, right?

On GNU/Linux, you can only resume such a native computation on the
same thread on which it was suspend, so this approach has limited
applicability there.