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-sessions
Description
L'appel à la fonction stat() ou lstat() est relativement coûteux en termes de temps d'exécution. Pour cela, le résultat du dernier appel à l'une des fonctions de statut, (voir la liste ci-dessous), est sauvegardé pour réutilisation ultérieure. Si vous voulez forcer la vérification du statut d'un fichier, dans le cas où le fichier aurait pu être modifié ou aurait disparu, vous devez utiliser la fonction clearstatcache() afin d'effacer de la mémoire les résultats du dernier appel à la fonction.
Sachez que PHP ne met pas en cache les informations concernant
un fichier inexistant. Si vous appelez file_exists()
sur un fichier qui n'existe pas, la fonction retournera false
jusqu'à ce que vous créiez le fichier. Si vous créez le fichier,
la fonction retournera true même si vous effacez le fichier.
Note:
Cette fonction met en cache des informations sur les fichiers. Vous n'avez donc besoin d'appeler clearstatcache() que si vous faites des opérations multiples sur le dossier, et que vous voulez avoir une version récente des informations.
Les fonctions affectées incluent : stat(), lstat(), file_exists(), is_writable(), is_readable(), is_executable(), is_file(), is_dir(), is_link(), filectime(), fileatime(), filemtime(), fileinode(), filegroup(), fileowner(), filesize(), filetype(), et fileperms().
Liste de paramètres
-
clear_realpath_cache -
Si l'on doit aussi vider le cache des chemins réels.
-
filename -
Nettoie le cache de chemin réel d'un fichier spécifique. Ne peut être utilisé que si le paramètre
clear_realpath_cachevauttrue.
Valeurs de retour
Aucune valeur n'est retournée.
Exemples
Exemple #1 Exemple avec clearstatcache()
<?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));
?>Résultat de l'exemple ci-dessus est similaire à :
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
add a note
User Contributed Notes 7 notes
vechenjivot at gmail dot com ¶
4 years ago
msaladna at apisnetworks dot com ¶
5 years ago
clearstatcache() does not canonicalize the path. clearstatcache(true, "/a/b/c") is different from clearstatcache(true, "/a/b//c").
matt_m at me dot com ¶
13 years ago
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.
David Spector ¶
6 years ago
Note 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.
bj at wjblack dot com ¶
9 years ago
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 :-( ).
Gabriel ¶
6 years ago
Definition of $filename parameter let's you think that it expects the filename only but it works if you give the path + filename also.
It should be more clear about this.
markandrewslade at gmail dot com ¶
14 years ago
On Linux, a forked process inherits a copy of the parent's cache, but after forking the two caches do not impact each other. The snippet below demonstrates this by creating a child and confirming outdated (cached) information, then clearing the cache, and getting new information.
<?php
function report($directory, $prefix = '') { printf('%sDoes %s exist? PHP says "%s"'. PHP_EOL, $prefix, $directory, is_dir($directory) ? 'yes' : 'no'); }
$target = './delete-me-before-running-statcache';
if (is_dir($target)) {
die("Delete $target before running.\n");
}
echo "Creating $target.\n";
mkdir($target) || die("Unable to create $target.\n");
report($target); // is_dir($target) is now cached as true
echo "Unlinking $target.\n";
rmdir($target) || die("Unable to unlink $target.\n");
// This will say "yes", which is old (inaccurate) information.
report($target);
if (($pid = pcntl_fork()) === -1) { die("Failed to pcntl_fork.\n"); }
elseif ($pid === 0) {
// child
report($target, '<<child>> ');
echo "<<child>> Clearing stat cache.\n";
clearstatcache();
report($target, '<<child>> ');
} else {
// parent
sleep(2); // move this to the child block to reverse the test.
report($target, '<<<parent>> ');
clearstatcache();
report($target, '<<<parent>> ');
}
?>
