clearstatcache()

(PHP 4, PHP 5, PHP 7)

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.

Note:

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

是否清除真实路径缓存

$filename

清除文件名指定的文件的真实路径缓存;只在$clear_realpath_cache为TRUE时启用

返回值

没有返回值。

更新日志

范例

Example #1clearstatcache()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));
?>

以上例程的输出类似于：

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

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.

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.

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 :-( ).

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

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.

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>> ');
}
?>