Boost logo

Boost :

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



Boost list run by bdawes at, gregod at, cpdaniel at, john at