Handling signals and performance issues.

[sragsdale at my-deja.com]

In article <meRU5.211$Mx.12164 at sjc-read.news.verio.net>,
  rayvd at nospam.firetail.org (Ray Van Dolson) wrote:
> I've written a small Python script that watches a logfile (kinda like
tail -
> f) and splits it into certain other files in real time.  I'm running
into
> two issues however that I haven't quite resolved yet to get this
script
> running as I'd like it.  Firstly, the program uses up a lot of CPU
time.
> This is almost certainly because of the way I'm watching the logfiles
for
> changes.  Basically it's like this:
>
> while 1:
>     	ln=inputLog.readline()
>     	if ln:
>     	    	processLine(ln)
>     	else:
>     	    	pass
>
> Much of the time of course there have been no changes to the logfile
and so
> it keeps looping, passing and waiting for a change.  While the system
> actually remains fast, watching 'top' shows that python is using up
all the
> cpu when it can.  Is there a better way to watch a file for changes
that
> doesn' use such a cpu consuming while loop?

Instead of looking into 'tail -f' to see how it does it, why not just
use it yourself?  The following program watches a logfile and prints out
the mirror image of the file, and it uses very minimal resources.
Useless, but it'll give you a starting point.


########################################33
import string,os
file = "logfile.txt"
fd = os.popen('tail -f '+file)
line = fd.readline()
while (line):
    line = list(line[:-1])
    line.reverse()
    line = string.join(line,'')
    print line
    line = fd.readline()


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