From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2008-06-23 12:14:54
David Abrahams wrote:
> Ion Gaztañaga wrote:
>
>> I plan to publish the article somewhere (supposing someone is crazy
>> enough to publish it ;-) ) but first I wanted to share this with
>> boosters to try to improve the article/library and know if developers
>> are interested in allocator issues. Comments are welcome!
>
> Hi Ion,
>
> Are you aware of the "scoped allocator" support that has recently been
> accepted into the WP?
Yes, thanks. I participated in some discussions with Pablo Halpern and
John Lakos to make Scoped allocators with non-scoped ones (basically
shared memory). Scoped allocators are basically mainly related to
allocator propagation and polymorphic allocators (plus the machinery to
implement this). My proposal has 3 different parts:
1) Realloc (expand in-place) and shrink to fit for std::vector. This
means reusing the old buffer (and avoiding moving or copying data) if
the allocator supports this.
2) Burst allocation: Some node containers (list, map...) just implement
range insertion with a loop:
for(/*every input element*/){
this->insert(pos, *inpit);
}
the idea here is to make a single to the allocator to allocate N nodes
with a single call. The allocator can just allocate a single big chunk
(thus, avoiding N lookups) and divide the big chunk in individually
deallocatable nodes.
3) Adaptive pools:
Some allocators, (like Boost.Pool) use simple segregated storage to
minimize node overhead. Sadly, they don't implicitly return memory to
the general-purpose allocator because the operation is costly
(Boost.Pool offers a purge() or release_memory() function to explicitly
trim allocated nodes). Adaptive pools are similar to simple segregated
storage allocators but they use alignment to automatically deallocate
memory while maintaining zero per-node payload. These allocators don't
need any allocator extension but they work extremely well with
burst-allocation because we can simplify bookkeeping operations that
have some impact when using single node allocation scheme.
In other words, Scoped Allocators and my proposal are completely
complementary.
Regards,
Ion