<?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.
*/
/*
* 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. In those cases please use the
* MySql back-end
*
* @author Chris Chabot <chabotc@google.com>
*/
class Google_FileCache extends Google_Cache {
private $path;
public function __construct() {
global $apiConfig;
$this->path = $apiConfig['ioFileCache_directory'];
}
private function isLocked($storageFile) {
// our lock file convention is simple: /the/file/path.lock
return file_exists($storageFile . '.lock');
}
private function createLock($storageFile) {
$storageDir = dirname($storageFile);
if (! is_dir($storageDir)) {
// @codeCoverageIgnoreStart
if (! @mkdir($storageDir, 0755, true)) {
// make sure the failure isn't because of a concurrency issue
if (! is_dir($storageDir)) {
throw new Google_CacheException("Could not create storage directory: $storageDir");
}
}
// @codeCoverageIgnoreEnd
}
@touch($storageFile . '.lock');
}
private function removeLock($storageFile) {
// suppress all warnings, if some other process removed it that's ok too
@unlink($storageFile . '.lock');
}
private function waitForLock($storageFile) {
// 20 x 250 = 5 seconds
$tries = 20;
$cnt = 0;
do {
// make sure PHP picks up on file changes. This is an expensive action but really can't be avoided
clearstatcache();
// 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks..
usleep(250);
$cnt ++;
} while ($cnt <= $tries && $this->isLocked($storageFile));
if ($this->isLocked($storageFile)) {
// 5 seconds passed, assume the owning process died off and remove it
$this->removeLock($storageFile);
}
}
private function getCacheDir($hash) {
// 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
return $this->path . '/' . substr($hash, 0, 2);
}
private function getCacheFile($hash) {
return $this->getCacheDir($hash) . '/' . $hash;
}
public function get($key, $expiration = false) {
$storageFile = $this->getCacheFile(md5($key));
// See if this storage file is locked, if so we wait up to 5 seconds for the lock owning process to
// complete it's work. If the lock is not released within that time frame, it's cleaned up.
// This should give us a fair amount of 'Cache Stampeding' protection
if ($this->isLocked($storageFile)) {
$this->waitForLock($storageFile);
}
if (file_exists($storageFile) && is_readable($storageFile)) {
$now = time();
if (! $expiration || (($mtime = @filemtime($storageFile)) !== false && ($now - $mtime) < $expiration)) {
if (($data = @file_get_contents($storageFile)) !== false) {
$data = unserialize($data);
return $data;
}
}
}
return false;
}
public function set($key, $value) {
$storageDir = $this->getCacheDir(md5($key));
$storageFile = $this->getCacheFile(md5($key));
if ($this->isLocked($storageFile)) {
// some other process is writing to this file too, wait until it's done to prevent hiccups
$this->waitForLock($storageFile);
}
if (! is_dir($storageDir)) {
if (! @mkdir($storageDir, 0755, true)) {
throw new Google_CacheException("Could not create storage directory: $storageDir");
}
}
// 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);
$this->createLock($storageFile);
if (! @file_put_contents($storageFile, $data)) {
$this->removeLock($storageFile);
throw new Google_CacheException("Could not store data in the file");
}
$this->removeLock($storageFile);
}
public function delete($key) {
$file = $this->getCacheFile(md5($key));
if (! @unlink($file)) {
throw new Google_CacheException("Cache file could not be deleted");
}
}
}
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