Boost logo

Boost :

Subject: Re: [boost] [block_ptr] Request for a review manager
From: Phil Bouchard (philippeb8_at_[hidden])
Date: 2016-02-07 11:24:55

On 02/07/2016 07:59 AM, Bjorn Reese wrote:
> On 02/06/2016 10:05 PM, Phil Bouchard wrote:
>> But it's like comparing apples with oranges because shared_ptr is a
>> smart pointer and block_ptr really is a memory manager there to replace
>> the garbage collector.
> The documentation is doing that apples and oranges comparison when it
> claims that the performance of block_ptr "is comparable to shared_ptr".
> Furthermore, that claim is questionable as the benchmarks show that
> block_ptr is slower by several factors. If the benchmarks are unfair,
> then you should design better ones.

Ideally the pool routines would offer a faster ordered_malloc() or the
main memory manager would offer some is_from() function because I need
to draw the line between the heap and the stack at run-time.

> The presentation claims "Constant complexity O(1) for all operations".
> Looking at the code I can see several loops (e.g. release() or redir()
> in block_header) so destruction does not appear to be constant.

You're right, destructions can be O(n) and assignments can be O(log(n))
worse case scenarios. I need to correct the documentation.

> I also have an unrelated comment about the documentation: the Reference
> section is very confusing. It lists lots of detail functions rather
> than the public API.
>> Unless the counter is intrusive but that's the thing because block_ptr
>> abstracts all of this and it is much less confusing to the end
>> developer. And I'm not sure how intrusive counters can deal with
>> multiple / virtual inheritance.
> Which intrusive counter are you talking about? Are you thinking of
> intrusive_ptr<T>?

I was thinking intrusive_ptr<> and make_shared<> which have both the
same optimum performance:

But while I don't see how intrusive_ptr<> deals well with multiple
inheritance, make_shared<> & shared_ptr<> needs to manage 2 pointers;
one for reference count and one for the pointed object.

block_ptr<> also manages 2 counters but it takes care of cyclic references.

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