(PHP 4, PHP 5, PHP 7, PHP 8)
clearstatcache — Clears file status cache
When you use stat(), lstat(), or any of the other functions listed in the affected functions list (below), PHP caches the information those functions return in order to provide faster performance. However, in certain cases, you may want to clear the cached information. For instance, if the same file is being checked multiple times within a single script, and that file is in danger of being removed or changed during that script's operation, you may elect to clear the status cache. In these cases, you can use the clearstatcache() function to clear the information that PHP caches about a file.
You should also note that PHP doesn't cache information about non-existent
files. So, if you call file_exists() on a file that
doesn't exist, it will return false until you create the file. If you
create the file, it will return true even if you then delete the file.
However unlink() clears the cache automatically.
Note:
This function caches information about specific filenames, so you only need to call clearstatcache() if you are performing multiple operations on the same filename and require the information about that particular file to not be cached.
Affected functions include stat(), lstat(), file_exists(), is_writable(), is_readable(), is_executable(), is_file(), is_dir(), is_link(), filectime(), fileatime(), filemtime(), fileinode(), filegroup(), fileowner(), filesize(), filetype(), and fileperms().
clear_realpath_cacheWhether to also clear the realpath cache.
filename
Clear the realpath cache for a specific filename only; only
used if clear_realpath_cache is true.
No value is returned.
Example #1 clearstatcache() example
<?php
$file = 'output_log.txt';
function get_owner($file)
{
$stat = stat($file);
$user = posix_getpwuid($stat['uid']);
return $user['name'];
}
$format = "UID @ %s: %s\n";
printf($format, date('r'), get_owner($file));
chown($file, 'ross');
printf($format, date('r'), get_owner($file));
clearstatcache();
printf($format, date('r'), get_owner($file));
?>The above example will output something similar to:
UID @ Sun, 12 Oct 2008 20:48:28 +0100: root UID @ Sun, 12 Oct 2008 20:48:28 +0100: root UID @ Sun, 12 Oct 2008 20:48:28 +0100: ross
unlink() does not clear the cache if you are performing file_exists() on a remote file like:
<?php
if (file_exists("ftp://ftp.example.com/somefile"))
?>
In this case, even after you unlink() successfully, you must call clearstatcache().
<?php
unlink("ftp://ftp.example.com/somefile");
clearstatcache();
?>
file_exists() then properly returns false.clearstatcache() does not canonicalize the path. clearstatcache(true, "/a/b/c") is different from clearstatcache(true, "/a/b//c").Not documented, but seems like clearstatcache() is clearing the cache only for the process it is being called from. I have 2 PHP scripts running simultaneously, and the first one does call clearstatcache(), but still the second one deadlocks, unless I call clearstatcache() in it too:
script1:
<?php
touch('system.lock');
...
unlink('system.lock');
clearstatcache(); // should be done by unlink?
?>
script2:
<?php
while (is_file('system.lock') {
sleep(1);
clearstatcache(); // without this, script 2 will deadlock forever!
}
?>
I also found this page, which leads to the same conclusion:
https://stackoverflow.com/questions/9251237/clearstatcache-include-path-sessionsNote that this function affects only file metadata. However, all the PHP file system functions do their own caching of actual file contents as well. You can use the "realpath_cache_size = 0" directive in PHP.ini to disable the content caching if you like. The default content caching timeout is 120 seconds.
Content caching is not a good idea during development work and for certain kinds of applications, since your code may read in old data from a file whose contents you have just changed.
Note: This is separate from the caching typically done by browsers for all GET requests (the majority of Web accesses) unless the HTTP headers override it. It is also separate from optional Apache server caching.Just to make this more obvious (and so search engines find this easier):
If you do fileops of any kind outside of PHP (say via a system() call), you probably want to clear the stat cache before doing any further tests on the file/dir/whatever. For example:
<?php
// is_dir() forces a stat call, so the cache is populated
if( is_dir($foo) ) {
system("rm -rf " . escapeshellarg($foo));
if( is_dir($foo) ) {
// ...will still be true, even if the rm succeeded, because it's just
// reading from cache, not re-running the stat()
}
}
?>
Pop a clearstatcache() after the system call and all is good (modulo a bit of a performance hit from having a cleared stat cache :-( ).