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Re: Signals, messages and exceptions

From: Leonardo Pereira
Subject: Re: Signals, messages and exceptions
Date: Fri, 1 Dec 2006 15:03:01 -0300

I think he isn't, Mach Exceptions are just another aproach of signals,
they were used on Mach_US and Lites to implement Unix-compatible
signals. The unique 'problem' is that Mach Exceptions handle not only
process but also threads, so, this is a very fundamental difference.

I also dunno why Mach Exception were not used to implement Unix
Signals on GNU Hurd/gLibC

Written by Roland McGrath on Sat, 7 Jul 2001 14:57:09 -0400 (EDT)
I think you are confused about what Mach exceptions are.

Written by Igor Khavkine on Sat, 7 Jul 2001 14:42:48 -0400
> I've been looking through the glibc code that handles signals
> for Hurd. At the same time I'm writing up a some docs on that
> so someone else won't have to do it again.
> What I'm surprised by is that signals are passed between processes
> using simple RPC messages. Mach has an exception facility
> for threads and tasks, so I thought that exceptions would be
> mapped to signals and vice versa. If a thread receives an exception,
> it is mapped to a signal. But this seems really strange, why
> have two ways of getting signals? It just duplicates the amount
> of code that needs to handle them.
> Both ways require a system call, so one is not more efficient then
> the other. The only reason I can see is that exceptions do not map
> directly to signals, but that's a very weak argument. Maybe it's
> one of those things that was done very long ago, no-one knows why,
> and no-one wants to change it?
> Thanks.
> Igor

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