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