Re: [Boost-users] progress_timer, incorrect timing

From: Ben Hutchings (ben.hutchings_at_[hidden])
Date: 2005-11-21 14:32:45

__PPS__ wrote:

>Will Bryant wrote:
>  
>
>>__PPS__ wrote:
>>
>>    
>>
>>>any ideas what's wrong, why clock() doesn't work anymore? 
>>>      
>>>
>>I'd hazard a guess that that's because it's measuring process CPU time 
>>rather than wall clock time.  If you replace the thing you're timing 
>>with some solid computation, does clock() suddenly start giving the 
>>results you expect?
>>
>>    
>>
>
>
>If I understand right, what you say is that these delays are due to 
>interaction with the os and they are not counted by clock (for this 
>process)?
>  
>
clock() is supposed to indicate how much time the processor has spent 
running the process. It should exclude the time the process spends 
waiting for input/output operations to complete, or waiting in the 
runnable queue while other processes run.

(Unfortunately in the MS C library (and maybe other C libraries for 
Windows) clock() indicates elapsed time since the process started, 
perhaps for compatibility with its behaviour under DOS, where the active 
process is never descheduled.)

Ben.