Re: [boost] Bug in pool not resetting next_size on purge_memory()

From: Brad Spencer (spencer_at_[hidden])
Date: 2002-10-21 14:26:15

On Fri, Oct 18, 2002 at 10:08:49AM -0400, scleary_at_[hidden] wrote:
> Yes, this is a bug for purge_memory() and release_memory().  I'll update it
> when I have time (probably not for a few weeks).  It will essentially do the
> same thing as your work-around.

Ok.  It is good to know that my workaround is correct.  Thank you.

> > Also, perhaps next_size should grow by a factor of 1.5 instead 2, as
> > is suggested by Andrei Alexandrescu in "Modern C++ Design" (I don't have
> > the page handy :)
> 
> When I wrote Boost.Pool, I considered two different growths for next_size:
>   next_size = next_size * 2;
> and
>   next_size = next_size * 2 + 1;
> 
> There's a disadvantage to the "*2+1" scheme: the "array doubling" scheme has
> a historical precedent, which makes it more likely that general-purpose
> allocation schemes are tuned to supply allocations of powers-of-2.  Before
> making this decision, I reviewed a few Standard library implementations (all
> the ones I had access to at the time), and found that std::vector used array
> doubling in every one.
> 
> I have not heard of this growth by 1.5 idea, and I just took a brief look
> through Andrei's book and couldn't find it.  Could you look up the
> reference, or maybe just describe the advantages of that approach?

That would be because I got my books mixed up :)  I didn't have them
with me when I wrote the original message.  I actually saw the 1.5
idea in Herb Sutter's More Effective C++ (Item 13).  He references
Andrew Koenig's September 1998 column in the Journal of
Object-Oriented Programming.  

The Sutter item is available online:

http://www.gotw.ca/gotw/043.htm

I could not find any online version of the JOOP article, although it
seems to be called "Why Are Vectors Efficient?".  It is referenced on
Koenig's biography page:

http://www.research.att.com/~ark/bibliography/joop.html

Sorry about the wild goose chase.

-- 
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