Date: Mon, 1 Nov 1999 16:53:10 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: jb@cimlogic.com.au (John Birrell) Cc: dufault@hda.com, julian@whistle.com, freebsd-arch@freebsd.org Subject: Re: Threads goals version III Message-ID: <199911012153.QAA19185@hda.hda.com> In-Reply-To: <19991102084448.A66172@freebsd1.cimlogic.com.au> from John Birrell at "Nov 2, 99 08:44:49 am"
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> On Mon, Nov 01, 1999 at 07:33:52AM -0500, Peter Dufault wrote:
> > > 4/ All threads in a processs see the same address space (exactly).
> >
> > Stacks too? Is that a rule implied from POSIX or one for portability?
>
> I think so. There is nothing to stop a thread from passing a pointer
> to something on it's stack to another thread, assuming that it will
> ensure that the stack will remain valid. This is common practice where
> one thread parents one or more child threads and wishes to share
> information with them.
Obviously he can't return though. Here's what I would
argue for in setting a standards document:
main()
{
int mainvar;
newthread(t1); /* t1 is a thread and it can access mainvar... */
sub();
}
sub()
{
int subvar;
newthread(t2); /* t2 can access subvar or mainvar, but maybe
* t1 can't access subvar.
* Maybe the stack just crossed a page boundary.
*/
while(1)
keep_stack_context();
}
Essentially threads would only be guaranteed access to stack variables
both in existence and valid when the thread is created. All stack
growth can be in separate address spaces.
If a stackless main() creates a bunch of threads at that level and
then idles those threads would have completely disjoint stacks.
Peter
--
Peter Dufault (dufault@hda.com) Realtime development, Machine control,
HD Associates, Inc. Safety critical systems, Agency approval
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