RFC: Hint parameter for allocators.

[Dhruv Matani]

On Fri, 2004-01-23 at 08:49, Loren James Rittle wrote:
> Dhruv Matani writes:
> > I'd like to discuss the specific use of the hint parameter of a standard
> > allocator when used to specify the region of memory the allocator should
> > prefer when choosing it for the current request.
> [...]
> 
> This is an interesting line of ideas.  I do wonder if the dynamic
> complexity outweighs memory layout advantage. 

That's the main question. I guess only studying a real application would
provide the answer.


>  In a static system
> build, where precompute time is a one-time cost, this can be a big win.

I did not get you here. What precompute time are you talking about?

> > 4. Does anyone know of an allocator that makes use of the hint parameter
> > for locality preservation?
> 
> Not in the context of a general allocator for use with STL.  How are
> you passing a hint in your current effort (code example, etc)?

First, we need to modify the list's base class so that get node accepts
hints. Then, modify the create_node function to accept hints. Then, in
the insert (iterator pos, const_reference Data) function, we change the
line that calls create_node (Data) to 
create_node (Data, pos._M_node->_M_prev);

pos._M_node->_M_prev is the last valid node in case of a non-empty list.

Then there's no need to change any driver program. Just re-compile any
existing test program that uses list and check the timings. I did that,
and did not notice any significant changes, so I suppose that:

1. It does not matter that much or:
2. In real application that runs for longer times, that would probably
make a difference?

Of course, you need to use an allocator that can make sense of the hint
parameter.


For the file attached, the controlling #define is USE_HINT_PARAMETER.
You can turn it on/off by simply commenting it away.



-- 
	-Dhruv Matani.
http://www.geocities.com/dhruvbird/


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