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From: Olaf Krzikalla (krzikalla_at_[hidden])
Date: 2005-05-01 05:52:11


frank_at_[hidden] wrote:
> Yep, now I understood. The whole thing is about laying out objects in
> memory in an efficient way. Sorry for always talking in critic, but I would
> love to suggest to think about memory allocators.
> Pool allocators can be utilised greatly to achieve memory layout for
> ideal cache heating. I missed that point in the efficiency discussion
> of intrusive containers versus non-intrusive containers.
Well, I'm not sure if this discussion belongs to the doc.
Anyway, let's think about the four points in 'Overviw: Properties of
intrusive containers' wrt pool allocators.
The first point: Depending on your RTL pool allocators may improve the
performance of the memory management. But it's a step in quantity, not
in quality. That is, there is still some memory management, while for
intrusive containers computing a node from a value and vice versa (to a
certain degree this operations are the counterparts of memory
management) is boiled down by the compiler to maybe three machine
instructions (in some cases it vanishes completely).
The second point: indeed it's possible to write a pool allocator in a
way, that at least the algorithm, that would need an intrusive container
otherwise, don't throw. Just preallocate enough elements beforehand (for
intrusive containers you do that implicitly).
The third point: I have no clue how to accomplish this task using
non-intrusive containers without a lot of additionally effort. And in
fact, this feature is very useful.
The fourth point: Regarding this discussion this is a non-issue IMHO. I
just wnat to point out, that clearing a std::list<T*> is as linear as
implicitly removing all elements stored in an ilist.

Best regards
Olaf Krzikalla

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