Re: MPS signals and Emacs

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> There are ambigupus and there are exact referenes. An object references
>> from at least one ambiguos reference cannot be moved, others can.
>> 
>> Where exact and where ambigous references are (or areas of these), one
>> has to tell MPS, of course. It's not like Boehm's collector where
>> everything is ambiguous.
>
> What do "exact reference" and "ambiguous reference" mean, in Emacs
> terms?

Ambiguour references are ones that could be a reference or a could as
well be a random bit pattern.

An example in Emacs is the control stack marking. I haven't looked at it
since I added that, so I don't know if that's still the same, but back
then it worked like this: Take a word W from the stack. See if W is
something that looks like a pointer into Lisp memeory (the red-black
tree, mem_xxx). See if W is a valid Lisp object start if that's the
case. If that's also the case, mark W as live. That means W might be
marked live, in principle, even if it isn't really.

Exact references are all references that aren't ambiguous. For example,
the name of a symbol had better be always a valid Lisp_Object.