On 28 March 2017 at 01:02, Yann Ylavic <ylavic....@gmail.com> wrote: > On Mon, Mar 27, 2017 at 3:55 PM, Ivan Zhakov <i...@visualsvn.com> wrote: >> On 24 March 2017 at 00:34, <yla...@apache.org> wrote: >>> + >>> +/** >>> + * Return the aligned (round up) size that an allocator would use for >>> + * the given size. >>> + * @param size The size to align >>> + * @return The aligned size (or zero on apr_size_t overflow) >>> + */ >>> +APR_DECLARE(apr_size_t) apr_allocator_align(apr_size_t size); >> What is the purpose of this API? Currently caller may use >> apr_memnode_t.endp to find actually allocated memory size. > > The purpose is to get this size before allocating any memory. > It is (newly) used in APR by apr_bucket_alloc_aligned_floor (itself > used by apr_bucket_file_set_buf_size), where the purpose is to take > into account and be precise with the overhead of the > (bucket_)allocator(s), and avoid over-allocating (wasted) memory. Hi Yann, thanks for explanation!
> >> >> Anyway I think it maybe worth to add apr_allocator_t argument to >> apr_allocator_align() function even currently allocation alignment is >> the same for all allocators. > > I see your point, but since there is no way to do this yet and that'd > require another API change, maybe we could do this at that time? > If you are concerned about the current name which would better fit an > allocator argument, let's use apr_allocator_default_align() for now... > or e.g. apr_allocator_align_of() later ;) > > Hmm, this makes me think that if apr_allocator_align() need an > alloctor, apr_bucket_alloc_aligned_floor() needs a bucket_alloc too, > and both functions may be less useful (or easy to use) if they require > the allocator the memory will finally be allocated on (say > apr_allocator_align() has to be used at the init time of an > application where the runtime allocator is not created yet). > > Also why would one want a different allocator alignment since (s)he > can apr_allocator_alloc() any size in the first place? The alignment > looks more like a property of the system than the allocator itself for > me... I'm not sure that *actual* allocation size could be predicted in all cases and possible apr_allocator_t implementation. Currently apr_bucket_alloc_aligned_floor() and apr_bucket_alloc() logic should be kept in sync, which is error prone imho. After looking to apr_bucket_alloc code I suggest to add apr_bucket_node_size(const void *node) that returns actual allocated node size. apr_file_bucket implementation could allocate desired buffer size and then query actual allocated size via apr_bucket_node_size. Apache Serf bucket_allocator uses similar approach. -- Ivan Zhakov
