Re: [boost] [xint] Third release is ready, requesting preliminary review

Subject: Re: [boost] [xint] Third release is ready, requesting preliminary review
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-05-03 08:04:31

Chad Nelson wrote:
> On 05/02/2010 03:19 AM, Jeffrey Hellrung wrote:
>
> > Regarding COW specifically:  I'm guessing COW will be a tough sell,
>
> I keep hearing that, but why? It's an internal detail, one
> that provides (or at least seems to) a very noticeable speed
> boost under some circumstances, and is disabled when it can't
> be safely used. Why would anyone, other than developers doing
> work on the library (i.e. me), care one way or another that
> the library uses it?

Those reviewing Boost libraries do care about internal details in many cases, as evidenced by the discussion surrounding your library.  Furthermore, the usual reaction to COW is to expect low performance in an MT program because it is too often a relic from single threaded design.  The typical examples of the benefits of using COW are eliminating the copying overhead of temporaries, which is served today by move semantics and copy elision, and unnecessary copies.  The latter merely require discipline to avoid or performance testing to identify.

There may be legitimate reason to use COW in your library, but because of the foregoing, you must ensure that you have applied move semantics correctly, write the code properly to avoid unnecessary copies, and prove that COW remains beneficial in a wide range of use cases in a MT test.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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