std::string::reserve()

[Paolo Carlini]

Neil Ferguson wrote:

>>> Can you make a bugzilla report about this?  
>>
> Will do - tonight, after the meeting I'm about to have. Do you want 
> the old patch included in the bugzilla report?

Yes, while you are at it, thanks in advance.

>> More specifically, I don't like the idea of, so to speak, 
>> anticipating in reserve the intentions of _M_clone , using at this 
>> upper level of abstraction a knowledge of _M_clone inner logic... 
>> Please, let me think about this issue a little more...
>
> I vaguely seem to recall lifting out the size calculation logic into a 
> separate method, so _M_clone and reserve could both call on it from 
> one place, if that helps any.

Sure, I remember that, nice. Still, in a sense we would do work in 
reserve which more properly belongs to _M_clone. Or, in other terms, we 
would compute rounded sizes two times, at two different levels of 
abstraction... something sounds wrong ;) We'll see...

> One result of this is that the exponential allocation policy can end 
> up allocating substantial amounts of memory which gets left unused, 
> and it would be nice to have the option of reclaiming it this way.

Definitely. Now we shrink to exact fit anything smaller than a memory page.

By the way, why don't you experiment a bit with changing the grow factor 
from 2.0 to 1.5, in _S_create? In some preliminary tests of mine the 
performance are not seriously affected while the amount of memory 
allocated decreases...

Paolo.