>>    >The best way to do this and make sure it is stealthy is by running a
>>    >subprocess.  The subprocess can run in parallel with Emacs.

>>    Hmm, i'm not sure if this is the best way?!

>If the primitives you need to do the job in Emacs LIsp can be slow, I
>see no other way to do the job except to avoid using those primitives.

I see another way:

IMHO reinventing the wheel for all these (potentially slow) elisp-
primitives is not worth the effort because IMHO for an ECB-user it is
much more important not being blocked. This can be achieved much easier
by implementing the stealthy task so they each key- or mouse-press
immediatelly interrupts a long-lasting action. So i do not really
elisp-threads if there is at least a elisp-tool which guarantees this
interrupt. AFAIK while-no-input is this tool . The only disadvantage
i can see is that it will be first available in Emacs 22. Therefore
my other question in another answer for with-local-quit mentioned by
Stefan (he said, this could be easily backported). AFAICS with-local-quit
would at least guarantee that C-g interrupts a long-lasting iteration
of a stealth task, right?

>Some day maybe that Emacs will have multi-threading, but that
>won't be soon.

I will not stop breathing until this feature will arise ;-)

Thansk for your help
Klaus