Re: Poison

[P.H.Welch@xxxxxxxxx]

Hi Larry,

> Here's an interesting thing I came across at work, that
> may or may not have relevance to "poison".
> 
> If an output is certainly going to an ALT input in its
> communication partner, and it is the last act of its
> process, a special "output-and-end-process" can be
> used and the outputting process never rescheduled. This
> works because the last act is always by the ALT input
> side. Of course, the ALT input has to know not to
> reschedule its partner.
> 
> The usefulness of this is that the ALT input side can
> free the output side's workspace (in a mixed static and
> dynamic memory allocation system I have).

Outputting POISON down a channel is the last thing a process does
only if it has no other input or output channels.  If it does,
if must send POISON down all its other outputs and wait to get
POISON back on all its inputs (discarding anything else that
arrives before that POISON).

All the above does go on in PARallel - so it's technically
right that the actual component of the PAR sending the POISON
does actually terminate after doing so.  But your advantage
is to free the POISONing process' workspace automatically
and the workspace of the POISONing component is tiny - it's
not the workspace of the parent process.

However, in the case of a process with one output channel
received always by an ALTing process, what you describe is
pretty neat!

Peter.