clearstatcache

(PHP 4, PHP 5, PHP 7)

clearstatcache — Clears file status cache

Descrierea

clearstatcache ( bool $clear_realpath_cache = false , string $filename = "" ) : void

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.

Notă:
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().

Parametri

clear_realpath_cache: Whether to clear the realpath cache or not.
filename: Clear the realpath and the stat cache for a specific filename only; only used if clear_realpath_cache is true.

Valorile întoarse

Nu este întoarsă nici o valoare.

Exemple

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));
?>

Exemplul de mai sus va afișa ceva similar cu:

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

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User Contributed Notes 7 notes

down

vechenjivot at gmail dot com ¶

4 years ago


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

down

msaladna at apisnetworks dot com ¶

4 years ago


clearstatcache() does not canonicalize the path. clearstatcache(true, "/a/b/c") is different from clearstatcache(true, "/a/b//c").

down

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.

down

David Spector ¶

5 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.

down

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 :-( ).

down

Gabriel ¶

5 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.

down

-38

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>> ');
}

?>

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