Re: need help making shell script use two CPUs/cores

[Camaleón <noelamac@gmail.com>]

On Sun, 09 Jan 2011 10:05:43 -0600, Stan Hoeppner wrote:

> I'm not very skilled at writing shell scripts.
> 
> #! /bin/sh
> for k in $(ls *.JPG); do convert $k -resize 1024 $k; done
> 
> I use the above script to batch re-size digital camera photos after I
> dump them to my web server.  It takes a very long time with lots of new
> photos as the server is fairly old, even though it is a 2-way SMP,
> because the script only runs one convert process at a time serially,
> only taking advantage of one CPU.  The convert program is part of the
> imagemagick toolkit.
> 
> How can I best modify this script so that it splits the overall job in
> half, running two simultaneous convert processes, one on each CPU?
> Having such a script should cut the total run time in half, or nearly
> so, which would really be great.

http://www.imagemagick.org/Usage/api/#speed

The above doc provides hints on how to speed-up image magick operations. 

Note that multi-threading should be automatically used whether possible, 
as per this paragraph:

***
# IM by default uses multiple threads for image processing operations. 
That means you can have the computer do two or more separate threads of 
image processing, it will be faster than a single CPU machine. 
***

I'm afraid you will have to find out whether your IM package was compiled 
with multi-threading capablities.

Greetings,

-- 
Camaleón