Re: limiting CPU usage

FROM : Alastair Houghton
DATE : Fri Nov 30 19:01:14 2007

On 30 Nov 2007, at 16:36, Alexander Cohen wrote:

> In that case, maybe you have an idea for me. I have a daemon that 
> runs and indexes all the images on a system. For each image, it 
> needs to open it up, get some info, close it and store that info. 
> This is very CPU consuming and can pretty much bring the system to a 
> halt after a while.


Are you sure it's the CPU usage that's the problem here?  The kind of 
thing you're talking about sounds like it should be I/O limited, not 
CPU limited on modern machines.  If it really is CPU limited, you may 
be using the wrong algorithm somewhere; try using Shark to find where 
the machine is spending its time.

Anyway, NSThread has -setThreadPriority:, which you can use.  If you 
aren't using Cocoa (in which case what are you doing posting this 
question to cocoa-dev?), you can also use various UNIX APIs (nice(), 
getpriority()/setpriority(), pthread_getschedparam()/setschedparam()).

Whatever you choose, you should be running at a low priority if you're 
CPU-bound (and contrary to popular belief, this will not make your 
code run slower... it just means that if the user wants to do 
something else at the same time, it will work better; if they don't, 
your program will take the same amount of time to run that it would 
have done before).

Kind regards,

Alastair.

--
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