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PhutilKeyValueCacheOnDisk.php
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Fri, Jan 3, 03:51

PhutilKeyValueCacheOnDisk.php
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<?php
/**
* Interface to a disk cache. Storage persists across requests.
*
* This cache is very slow compared to caches like APC. It is intended as a
* specialized alternative to APC when APC is not available.
*
* This is a highly specialized cache and not appropriate for use as a
* generalized key-value cache for arbitrary application data.
*
* Also note that reading and writing keys from the cache currently involves
* loading and saving the entire cache, no matter how little data you touch.
*
* @task kvimpl Key-Value Cache Implementation
* @task storage Cache Storage
*/
final class PhutilKeyValueCacheOnDisk extends PhutilKeyValueCache {
private $cache = array();
private $cacheFile;
private $lock;
private $wait = 0;
/* -( Key-Value Cache Implementation )------------------------------------- */
public function isAvailable() {
return true;
}
/**
* Set duration (in seconds) to wait for the file lock.
*/
public function setWait($wait) {
$this->wait = $wait;
return $this;
}
public function getKeys(array $keys) {
$now = time();
$results = array();
$reloaded = false;
foreach ($keys as $key) {
// Try to read the value from cache. If we miss, load (or reload) the
// cache.
while (true) {
if (isset($this->cache[$key])) {
$val = $this->cache[$key];
if (empty($val['ttl']) || $val['ttl'] >= $now) {
$results[$key] = $val['val'];
break;
}
}
if ($reloaded) {
break;
}
$this->loadCache($hold_lock = false);
$reloaded = true;
}
}
return $results;
}
public function setKeys(array $keys, $ttl = null) {
if ($ttl) {
$ttl_epoch = time() + $ttl;
} else {
$ttl_epoch = null;
}
$dicts = array();
foreach ($keys as $key => $value) {
$dict = array(
'val' => $value,
);
if ($ttl_epoch) {
$dict['ttl'] = $ttl_epoch;
}
$dicts[$key] = $dict;
}
$this->loadCache($hold_lock = true);
foreach ($dicts as $key => $dict) {
$this->cache[$key] = $dict;
}
$this->saveCache();
return $this;
}
public function deleteKeys(array $keys) {
$this->loadCache($hold_lock = true);
foreach ($keys as $key) {
unset($this->cache[$key]);
}
$this->saveCache();
return $this;
}
public function destroyCache() {
Filesystem::remove($this->getCacheFile());
return $this;
}
/* -( Cache Storage )------------------------------------------------------ */
/**
* @task storage
*/
public function setCacheFile($file) {
$this->cacheFile = $file;
return $this;
}
/**
* @task storage
*/
private function loadCache($hold_lock) {
if ($this->lock) {
throw new Exception('Trying to loadCache() with a lock!');
}
$lock = PhutilFileLock::newForPath($this->getCacheFile().'.lock');
try {
$lock->lock($this->wait);
} catch (PhutilLockException $ex) {
if ($hold_lock) {
throw $ex;
} else {
$this->cache = array();
return;
}
}
try {
$this->cache = array();
if (Filesystem::pathExists($this->getCacheFile())) {
$cache = unserialize(Filesystem::readFile($this->getCacheFile()));
if ($cache) {
$this->cache = $cache;
}
}
} catch (Exception $ex) {
$lock->unlock();
throw $ex;
}
if ($hold_lock) {
$this->lock = $lock;
} else {
$lock->unlock();
}
}
/**
* @task storage
*/
private function saveCache() {
if (!$this->lock) {
throw new Exception(
'Call loadCache($hold_lock=true) before saveCache()!');
}
// We're holding a lock so we're safe to do a write to a well-known file.
// Write to the same directory as the cache so the rename won't imply a
// copy across volumes.
$new = $this->getCacheFile().'.new';
Filesystem::writeFile($new, serialize($this->cache));
Filesystem::rename($new, $this->getCacheFile());
$this->lock->unlock();
$this->lock = null;
}
/**
* @task storage
*/
private function getCacheFile() {
if (!$this->cacheFile) {
throw new Exception('Call setCacheFile() before using a disk cache!');
}
return $this->cacheFile;
}
}

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