Re: [boost] Proposal for #pragma once support

Subject: Re: [boost] Proposal for #pragma once support
From: Christopher Jefferson (chris_at_[hidden])
Date: 2009-06-10 05:11:13

On 10 Jun 2009, at 02:13, Jeff Flinn wrote:

> Chandrashekhar Kumar wrote:
>> On Tue, Jun 9, 2009 at 11:33 PM, Christopher Jefferson <
>> chris_at_[hidden]> wrote:
>>> RedundantGuard: 0.130s
>>> Nothing: 0.170s
>>> PragmaOnce: 0.710s
>>>
>>> So PragmaOnce is over 7 times slower. That time is almost entirely  
>>> in the
>>> 'sys' column, so I suspect it querying files to check if they are  
>>> identical
>>> or not.
>>>
>>> Chris
>
>
> Did you check repeatablity of these measurements? Disk caches can  
> significantly skew timings. Were these separate files with the  
> various include guard techniques? If so is the disk fully defragged?

Yes, I ran each experiment 10 times and averaged.

Just as a sanity check, I wrapped each #pragma once in a #ifdef  
BOOST_USE_PRAGMA_ONE, and then not defining it. As expected, the  
result is indistinguishable from the 'Nothing' choice.

I just wanted to check it wouldn't confuse any kind of 'auto header- 
guard' detection gcc might have.

Chris