Re: exception systems

[Olin Shivers <shivers@lambda.ai.mit.edu>]

   Your CMU/Mach bias is showing through...

I wish. I assure you that in my CMU days, the Mach guys had little interest
in the opinions of a wimp Scheme hacker who had never written a line of
kernel code.

   I think you are assuming that you need a full context switch when an
   interrupt arrives.  This is unnecessary, and the point of my previous
   message.

What you are proposing certainly provides a way to get very cheap
interrupts -- it is the way that Henry Massalin gets low-overhead
interrupts in Synthesis, for example.

But I don't like the semantics of thinking of it as an unplanned-for
subroutine call. It's really just that the interrupt handler is borrowing
the current thread's resources to execute for a little while. But I
think of that handler as another entity; this resource-stealing trick
is just an efficiency hack.

   One of the beauties of using Scheme for interrupt handling is that a
   closure is an incredibly effective mini-context.

Yes!
    -Olin