On Wed, Sep 26, 2018 at 10:20 AM Daniel Shahaf <d...@daniel.shahaf.name> wrote:
> Jim Jagielski wrote on Wed, 26 Sep 2018 11:09 -0400: > > At ApacheCon's welcoming event last night, Greg, Sander and I were > > chatting and Greg reminded us that the Subversion project "learned a lot > > about using APR pools" and it seems to me that a lot of that knowledge > > is likely missing in httpd-land. I also know that some of that has been > > backported back to APR itself, but I am wondering (as I am wont to do), > > if we couldn't do a better job here. I am sure that there are things in > > svn that could be easily and readily folded back into APR w/o breaking > > anything. > > > > I know that some of that influenced Greg's PoCore work, but it would be > > really cool if someone in Subversion could maybe point out some of those > > improvements and "lessons learned" so that both APR and httpd could > > benefit. > > For starters, here's what we've already written down: > > > https://subversion.apache.org/docs/community-guide/conventions.html#apr-pools > > I would especially point out the result_pool/scratch_pool distinction: > each function gets *two* pools, one in which to allocate the return > value, and one whose lifetime is defined as "the pool may be deleted at > any time after the function returns". > > For example, when one calls a function declared as: > . > apr_status_t find_foo(foo_t *outparam, ..., apr_pool_t *result_pool, > apr_pool_t *scratch_pool) > . > then on return *outparam will be allocated in result_pool, and > apr_pool_clear(scratch_pool) may be called as soon as find_foo() > returned. Yup. > Thus, scratch_pool is passed into the result_pool formal > parameter of functions find_foo() calls, is the pool iterpools are created > as subpools of, etc. . > This is a bit unclear, so skip this and go read the page :-) > I'm sure Greg is subscribed to at least one of these lists and will add > anything I forgot :) All three, actually :-) ... and the pointer to the coding convention page is exactly what I wanted to point the other groups at. iterpool, scratch_pool, and result_pool are the KEY three concepts that we learned while working on Subversion. Also relying on your *caller* to know more about memory management / lifetimes. The conventions page does a really great job of describing what we learned, and we're here to expand/answer where it isn't (and #fixthedoc :-P ), and/or provide further examples to clarify. Cheers, -g
