Re: Emacs design and architecture. How about copy-on-write?

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> If we need to lock 99.99% of Emacs "single" variables, it is easier to
> lock everything.  Faster, too.

Interlocking variables is not necessary.  Extant buses guarantee that
word-sized (Lisp_Object) writes and reads from one CPU are always
coherently propagated to other processors.  And otherwise, interlocking
every global variables would incur an extreme performance penalty; two
extra load-locked / store-conditional pairs (or interlocked
instructions) for each read or write at the minimum.

Interlocking Lisp_Objects themselves is only mandatory under wide int
builds, where the size of each object is larger than the machine's word
size.  Supporting such builds in a multiprocessing Emacs will be an
extreme burden that I don't think we should shoulder.