clearstatcache

(PHP 4, PHP 5, PHP 7, PHP 8)

clearstatcache — 清除文件状态缓存

说明

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

当使用 stat()，lstat() 或者任何列在受影响函数表（见下面）中的函数时，PHP 将缓存这些函数的返回信息以提供更快的性能。然而在某些情况下，你可能想清除被缓存的信息。例如如果在一个脚本中多次检查同一个文件，而该文件在此脚本执行期间有被删除或修改的危险时，你需要清除文件状态缓存。这种情况下，可以用 clearstatcache() 函数来清除被 PHP 缓存的该文件信息。

必须注意的是，对于不存在的文件，PHP 并不会缓存其信息。所以如果调用 file_exists() 来检查不存在的文件，在该文件没有被创建之前，它都会返回 false。如果该文件被创建了，就算以后被删除，它都会返回 true 函数 unlink() 会自动清除该缓存.

注意:
本函数缓存特定文件名的信息，因此只在对同一个文件名进行多次操作并且需要该文件信息不被缓存时才需要调用 clearstatcache()。

受影响的函数包括 stat()， lstat()， file_exists()， is_writable()， is_readable()， is_executable()， is_file()， is_dir()， is_link()， filectime()， fileatime()， filemtime()， fileinode()， filegroup()， fileowner()， filesize()， filetype() 和 fileperms()。

参数

clear_realpath_cache: 是否也清除真实路径缓存
filename: 仅清除指定文件名的真实路径缓存; 只在 clear_realpath_cache 为 true 时启用。

返回值

没有返回值。

示例

示例 #1 clearstatcache() 例子

<?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));
?>

以上示例的输出类似于：

 
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 ¶

3 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 ¶

3 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 ¶

12 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.

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David Spector ¶

4 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 ¶

8 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 ¶

4 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 ¶

13 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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