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Re: exception systems

|   Date: Thu, 18 Apr 1996 15:26:10 -0400
|   From: Olin Shivers <shivers@lambda.ai.mit.edu>
|   Cc: blume@cs.princeton.edu, will@ccs.neu.edu, rrrs-authors@mc.lcs.mit.edu
|   Reply-To: shivers@ai.mit.edu
|   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 last thing.  Even in a fully threaded model, you still need the
ability to inject code into another thread.  This is no different from
an interrupt, even if it happens synchronously to the scheduler.  As
far as the injected thread was concerned, the thread was interrupted.