YAMAMOTO Takashi wrote:
> how about a user-kernel shared variable used to indicate if
> any upcall handler is executing or not?
> (iirc, freebsd kse does a similar thing)

This would work beautifully with the current implementation
since it only supports a single virtual processor.

Multiple virtual processors would cause trouble since user
level threads have no way of knowing the virtual processor they
are running on.
I don't think sharing the variable between virtual processors is
an option.

Stephan