Re: Signals, messages and exceptions

[Leonardo Pereira]

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