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<?php |
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/* |
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* Copyright 2008 Google Inc. |
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* |
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* Licensed under the Apache License, Version 2.0 (the "License"); |
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* you may not use this file except in compliance with the License. |
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* You may obtain a copy of the License at |
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* |
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* http://www.apache.org/licenses/LICENSE-2.0 |
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* |
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* Unless required by applicable law or agreed to in writing, software |
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* distributed under the License is distributed on an "AS IS" BASIS, |
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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* See the License for the specific language governing permissions and |
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* limitations under the License. |
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*/ |
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|
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/* |
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* This class implements a basic on disk storage. While that does |
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* work quite well it's not the most elegant and scalable solution. |
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* It will also get you into a heap of trouble when you try to run |
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* this in a clustered environment. In those cases please use the |
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* MySql back-end |
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* |
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* @author Chris Chabot <chabotc@google.com> |
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*/ |
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class Google_FileCache extends Google_Cache { |
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private $path; |
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|
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public function __construct() { |
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global $apiConfig; |
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$this->path = $apiConfig['ioFileCache_directory']; |
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} |
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|
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private function isLocked($storageFile) { |
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// our lock file convention is simple: /the/file/path.lock |
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return file_exists($storageFile . '.lock'); |
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} |
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|
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private function createLock($storageFile) { |
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$storageDir = dirname($storageFile); |
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if (! is_dir($storageDir)) { |
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// @codeCoverageIgnoreStart |
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if (! @mkdir($storageDir, 0755, true)) { |
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// make sure the failure isn't because of a concurrency issue |
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if (! is_dir($storageDir)) { |
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throw new Google_CacheException("Could not create storage directory: $storageDir"); |
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} |
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} |
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// @codeCoverageIgnoreEnd |
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} |
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@touch($storageFile . '.lock'); |
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} |
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|
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private function removeLock($storageFile) { |
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// suppress all warnings, if some other process removed it that's ok too |
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@unlink($storageFile . '.lock'); |
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} |
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|
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private function waitForLock($storageFile) { |
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// 20 x 250 = 5 seconds |
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$tries = 20; |
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$cnt = 0; |
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do { |
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// make sure PHP picks up on file changes. This is an expensive action but really can't be avoided |
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clearstatcache(); |
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// 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks.. |
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usleep(250); |
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$cnt ++; |
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} while ($cnt <= $tries && $this->isLocked($storageFile)); |
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if ($this->isLocked($storageFile)) { |
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// 5 seconds passed, assume the owning process died off and remove it |
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$this->removeLock($storageFile); |
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} |
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} |
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|
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private function getCacheDir($hash) { |
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// use the first 2 characters of the hash as a directory prefix |
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// this should prevent slowdowns due to huge directory listings |
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// and thus give some basic amount of scalability |
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return $this->path . '/' . substr($hash, 0, 2); |
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} |
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|
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private function getCacheFile($hash) { |
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return $this->getCacheDir($hash) . '/' . $hash; |
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} |
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|
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public function get($key, $expiration = false) { |
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$storageFile = $this->getCacheFile(md5($key)); |
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// See if this storage file is locked, if so we wait upto 5 seconds for the lock owning process to |
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// complete it's work. If the lock is not released within that time frame, it's cleaned up. |
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// This should give us a fair amount of 'Cache Stampeding' protection |
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if ($this->isLocked($storageFile)) { |
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$this->waitForLock($storageFile); |
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} |
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if (file_exists($storageFile) && is_readable($storageFile)) { |
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$now = time(); |
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if (! $expiration || (($mtime = @filemtime($storageFile)) !== false && ($now - $mtime) < $expiration)) { |
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if (($data = @file_get_contents($storageFile)) !== false) { |
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$data = unserialize($data); |
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return $data; |
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} |
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} |
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} |
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return false; |
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} |
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|
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public function set($key, $value) { |
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$storageDir = $this->getCacheDir(md5($key)); |
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$storageFile = $this->getCacheFile(md5($key)); |
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if ($this->isLocked($storageFile)) { |
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// some other process is writing to this file too, wait until it's done to prevent hickups |
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$this->waitForLock($storageFile); |
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} |
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if (! is_dir($storageDir)) { |
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if (! @mkdir($storageDir, 0755, true)) { |
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throw new Google_CacheException("Could not create storage directory: $storageDir"); |
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} |
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} |
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// we serialize the whole request object, since we don't only want the |
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// responseContent but also the postBody used, headers, size, etc |
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$data = serialize($value); |
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$this->createLock($storageFile); |
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if (! @file_put_contents($storageFile, $data)) { |
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$this->removeLock($storageFile); |
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throw new Google_CacheException("Could not store data in the file"); |
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} |
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$this->removeLock($storageFile); |
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} |
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|
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public function delete($key) { |
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$file = $this->getCacheFile(md5($key)); |
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if (! @unlink($file)) { |
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throw new Google_CacheException("Cache file could not be deleted"); |
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} |
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} |
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} |
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|
