Aurélien Campéas writes:
> Hello,
>
> pp 258-259 of CTM are about multiple readers for streams ...
>
> local Xs S1 S2 S3 in
> thread Xs={Generate 0 150000} end
> thread S1={Sum Xs 0} end
> thread S2={Sum Xs 0} end
> ...
> end
>
> this implies that the stream a) is not really consummed by the threads,
> hence b) the 150000 elements reside in memory c) it looks quite
> difficult how to decide when to release them
>
> I'm really puzzled with this aspect of streams ... (I hope this isn't a
> FAQ).
>
All data that is no longer reachable from any thread in the system is
garbage and can be collected by a garbage collection. So, if Xs isn't
used in the ... part of your example then any portion of Xs that has
been processed by both Sum threads will be garbage. That is, we don't
need to wait until the Sum threads have completed before reclaiming
the space used by the finished with portion of Xs.
So, in the best case if we were lucky with the scheduling of threads
(you won't be!) then the above program could run in constant space.
If we generated Xs lazily (sec 4.5 of CTM) and only consumed it once
then it would run in constant space.
regards
k
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