scalability of perl cgi programs that load text files

Suppose you have a perl program that is called by a web page to
generate another web page. The program is written to load data from a
text file on the server and make certain substitutions in the loaded
text prior to the output of html.

If one user is on the site, it should not be a problem. If many users
try to access it nearly simultaneously, will it be a problem?

example:

file: text.txt

I am <adjective>.

file: process.perl

....
open INPUT, "./text".".txt";
@list = <INPUT>;
close INPUT;
foreach(@list)
{
s/<adjective>/stupid/g;
}
....

What happens here when a second user causes the program to run when
the first user is at the point where the text file is opened and not
yet closed?

>Suppose you have a perl program that is called by a web page to
>generate another web page. The program is written to load data from a
>text file on the server and make certain substitutions in the loaded
>text prior to the output of html.

>If one user is on the site, it should not be a problem. If many users
>try to access it nearly simultaneously, will it be a problem?

That's what file locking is designed for.. look into flock()..

Regards,
Chris

P.S. You do realise this a PHP group ?

On 21 Aug 2004 22:33:08 -0700, mail@affordablemedicalsoftware.com (MJL) wrote:

>Suppose you have a perl program that is called by a web page to
>generate another web page.

Suppose you post this Perl program to a PHP newsgroup... what is the expected
result? :-) Try comp.lang.perl.misc.

> The program is written to load data from a
>text file on the server and make certain substitutions in the loaded
>text prior to the output of html.
>
>If one user is on the site, it should not be a problem. If many users
>try to access it nearly simultaneously, will it be a problem?

Not if it's read-only. If it's updated, then yes, you'll have multiple
processes stomping on each other's data, in which case you need to put locking
around it, or better, use a database, as concurrent access is one of the
several main reasons you'd use a database over a flat file.

>example:
>
>open INPUT, "./text".".txt";

You probably want to be specifying a filemode here - assuming you just want
'r' (read-only).

>What happens here when a second user causes the program to run when
>the first user is at the point where the text file is opened and not
>yet closed?

Presumably operating-system dependent, but it would have to be a pretty duff
operating system to disallow read-only access to multiple processes.

--
Andy Hassall / <andy@andyh.co.uk> / <http://www.andyh.co.uk>
<http://www.andyhsoftware.co.uk/space> Space: disk usage analysis tool

> Regards,
> Chris
>
> P.S. You do realise this a PHP group ?

Oh, man. I am so embarrassed. Sorry. I have been so entangled in
playing with code in the two languages this weekend that I really
screwed up and posted to the wrong group. My perl script is
generating HTML and PHP. Sorry again.

"MJL" wrote:
> Suppose you have a perl program that is called by a web page to
> generate another web page. The program is written to load data
from a
> text file on the server and make certain substitutions in the
loaded
> text prior to the output of html.
>
> If one user is on the site, it should not be a problem. If many
users
> try to access it nearly simultaneously, will it be a problem?
>
> example:
>
> file: text.txt
>
> I am <adjective>.
>
> file: process.perl
>
> ....
> open INPUT, "./text".".txt";
> @list = <INPUT>;
> close INPUT;
> foreach(@list)
> {
> s/<adjective>/stupid/g;
> }
> ....
>
> What happens here when a second user causes the program to run when
> the first user is at the point where the text file is opened and
not
> yet closed?

This is a php newsgroup. Try a perl newsgroup for better coverage.

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