11.21.06
Caching in PHP (Flat-File Caches)
Flat-File caches is useful in PHP applications. Applications simply include cached file or directly use it as a file.
The main problem is reading and writing simultaneously in flat-file caching. There are two ways to avoid the problem.
1) Using file locks (flock — Portable advisory file locking).
2) Using temporary files.
Here is an example of flat-file caching with temporary files.
///////////////////////////////////////////////////////////////////////////////
<?php
$cached_file = basename($_SERVER[’PHP_SELF’]) . “.cache”;
if (file_exists($cached_file)) {
include($cached_file);
exit;
}
$temp_file =tempnam(”.”, $cached_file);
$fp_temp = fopen($temp_file, “w”);
ob_start();
?>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
<html>
<head>
<meta http-equiv=”Content-Type” content=”text/html; charset=utf-8″>
<title>Caching in PHP (Flat-File Caches)</title>
</head>
<body>
Here is an example of flat-file caching with temporary files.
</body>
</html>
<?php
if ($fp_temp) {
$buffered_contents = ob_get_contents();
fwrite($fp_temp, $buffered_contents);
fclose($fp_temp);
rename($temp_file, $cached_file);
}
ob_end_flush();
?>
///////////////////////////////////////////////////////////////////////////////
Download the code
The specification requires that the action of the rename function be atomic so if more than one process rename its temporary file, the last one succeeds.
It is obvious that our flat-file caching mechanism does not invalidate the cache! Our cache is forever! I will write about Cache Invalidation soon:)
Note :
When safe_mode is enabled, PHP checks whether the directory in which you are about to operate has the same UID (owner) as the script that is being executed.
References
- Advanced PHP Programming by George Schlossnagle.