Re: advice needed for multi-threading patch

[Stefan Monnier]

>> Emacs's stack scanning already has to check both Lisp_Object values
>> (i.e. tagged pointers) and plain direct untagged pointers.  This was
>> needed IIRC because even if the C code appears to hold on to
>> a Lisp_Object value, the optimizer may get rid of it and only keep the
>> untagged pointer.
> Does that mean that GC_USE_GCPROS_AS_BEFORE doesn't work reliably?

It's very little tested, but it should work reliably.  The reason it
works reliably is that the GCPRO macros cause the Lisp_Object variables
to be accessed via "&" and their address is stored in a globally
accessible data structure, so the compiler cannot optimize those
variables away, or even keep them in registers.


        Stefan