Path: utzoo!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!hpda!hpcupt1!hpisod2!decot
From: decot@hpisod2.HP.COM (Dave Decot)
Newsgroups: comp.unix.questions
Subject: Re: tail -f
Message-ID: <10650037@hpisod2.HP.COM>
Date: 10 Dec 88 01:50:13 GMT
References: <412@fedeva.UUCP>
Organization: Hewlett Packard, Cupertino
Lines: 17

> >Can someone please tell me how 'tail -f' works?.  Obviously, it does not
> >do a busy loop while doing a stat on the file.  I know that it has got
> >to be blocked, waiting for the length to change, but how does it get
> >notified of a change?  Thanks in advance for any responses.
> 
> Oh, dear, he used the "O" word.  One should be careful using that
> word....
> 
> In fact, it *does* do a busy loop while doing "read"s (not "stat"s) of
> the file; it just sleeps 1 second between attempts to "read", so it
> doesn't burn quite so much CPU doing it.  If there were some way for it
> to block waiting for the length to change, it would; however, there
> isn't any such way. 

I suppose it could use select(2)...

Dave