Re: Why is VC++ STL so slow?
"Earl Purple" <earlpurple@gmail.com> wrote in message
news:1159660875.090309.84560@c28g2000cwb.googlegroups.com...
P.J. Plauger wrote:
They favor allocators that optimize for speed, often at the expense
of wasting or even failing to release storage. We provide by default
a simple allocator that calls new and delete for each map node.
(Our add-on library, available at our web site, comes with an
assortment of allocators to choose among if you don't like the
default.) It's also possible that the underlying heap manager may
contribute, but I doubt it.
As for the insert and find machinery, they're too similar to
account for the difference you report.
You are obviously more expert at this than me but I would have thought
you would not call new and delete on one map node at a time but instead
allocate a block of them in advance, similar to what you do in vector.
Quite often the one-at-a-time approach has the best performance,
if only because of its simplicity.
When you say they fail to release storage, I guess you mean that they
use a similar behaviour to string and vector, thus even if elements are
removed, the memory is retained for possible re-use.
Well yes, but string and vector deal with a single block of storage
at any given time. A pooled allocator shares multiple nodes across
all maps of a given type, which introduces synchronization issues in
a multithreaded system. And when I say they fail to release storage,
I mean even at program termination.
P.J. Plauger
Dinkumware, Ltd.
http://www.dinkumware.com
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