text file behavior

[Karl Hungus]

I have a question about the behavior of a text file thats being written and
read to.

Say Im using an XML file as the database for my little application. Users
come to my site and the file is read and parsed and coverted to some display
in html. On another page users can add information that updates this XML
file.

Is there any risk in this approach? While the XML file is being written to,
what is its readabililty? And vise-versa. Assuming Im using the standard
read write functions for files in PHP, will the read wait for a write to
finish, etc.

Thanks in advance

[Pedro Graca]

Re: text file behavior

Karl Hungus wrote:[color=blue]
> I have a question about the behavior of a text file thats being written and
> read to.[/color]
(snip)[color=blue]
> Is there any risk in this approach? While the XML file is being written to,
> what is its readabililty? And vise-versa. Assuming Im using the standard
> read write functions for files in PHP, will the read wait for a write to
> finish, etc.[/color]

I think you should use the file-locking mechanism to avoid risk.

http://www.php.net/flock

<?php
$xml = '/path/to/xmlfile.xml';
$f = fopen($xml, 'w') or die('cannot open file ' . $xml);

// try $n times to lock the file
// waiting 1 milli-second between each attempt
$n = 6;
while ($n) {
if (flock($f, LOCK_EX)) break;
--$n;
usleep(1000);
}
if ($n == 0) die('Could not lock the file' . $xml)

// write data
fwrite($f, 'whatever');

// unlock and close the file
flock($f, LOCK_UN);
fclose($f);
?>
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