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<?php
/*
* Copyright 2008 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
require_once "Google/Cache/Abstract.php";
require_once "Google/Cache/Exception.php";
/*
* This class implements a basic on disk storage. While that does
* work quite well it's not the most elegant and scalable solution.
* It will also get you into a heap of trouble when you try to run
* this in a clustered environment.
*
* @author Chris Chabot <chabotc@google.com>
*/
class Google_Cache_File extends Google_Cache_Abstract
{
const MAX_LOCK_RETRIES = 10;
private $path;
private $fh;
public function __construct(Google_Client $client)
{
$this->path = $client->getClassConfig($this, 'directory');
}
public function get($key, $expiration = false)
{
$storageFile = $this->getCacheFile($key);
$data = false;
if (!file_exists($storageFile)) {
return false;
}
if ($expiration) {
$mtime = filemtime($storageFile);
if ((time() - $mtime) >= $expiration) {
$this->delete($key);
return false;
}
}
if ($this->acquireReadLock($storageFile)) {
$data = fread($this->fh, filesize($storageFile));
$data = unserialize($data);
$this->unlock($storageFile);
}
return $data;
}
public function set($key, $value)
{
$storageFile = $this->getWriteableCacheFile($key);
if ($this->acquireWriteLock($storageFile)) {
// We serialize the whole request object, since we don't only want the
// responseContent but also the postBody used, headers, size, etc.
$data = serialize($value);
$result = fwrite($this->fh, $data);
$this->unlock($storageFile);
}
}
public function delete($key)
{
$file = $this->getCacheFile($key);
if (file_exists($file) && !unlink($file)) {
throw new Google_Cache_Exception("Cache file could not be deleted");
}
}
private function getWriteableCacheFile($file)
{
return $this->getCacheFile($file, true);
}
private function getCacheFile($file, $forWrite = false)
{
return $this->getCacheDir($file, $forWrite) . '/' . md5($file);
}
private function getCacheDir($file, $forWrite)
{
// use the first 2 characters of the hash as a directory prefix
// this should prevent slowdowns due to huge directory listings
// and thus give some basic amount of scalability
$storageDir = $this->path . '/' . substr(md5($file), 0, 2);
if ($forWrite && ! is_dir($storageDir)) {
if (! mkdir($storageDir, 0755, true)) {
throw new Google_Cache_Exception("Could not create storage directory: $storageDir");
}
}
return $storageDir;
}
private function acquireReadLock($storageFile)
{
return $this->acquireLock(LOCK_SH, $storageFile);
}
private function acquireWriteLock($storageFile)
{
$rc = $this->acquireLock(LOCK_EX, $storageFile);
if (!$rc) {
$this->delete($storageFile);
}
return $rc;
}
private function acquireLock($type, $storageFile)
{
$mode = $type == LOCK_EX ? "w" : "r";
$this->fh = fopen($storageFile, $mode);
$count = 0;
while (!flock($this->fh, $type | LOCK_NB)) {
// Sleep for 10ms.
usleep(10000);
if (++$count < self::MAX_LOCK_RETRIES) {
return false;
}
}
return true;
}
public function unlock($storageFile)
{
if ($this->fh) {
flock($this->fh, LOCK_UN);
}
}
}
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