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LockRegistry.php
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<?php
/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace Symfony\Component\Cache;
use Psr\Log\LoggerInterface;
use Symfony\Contracts\Cache\CacheInterface;
use Symfony\Contracts\Cache\ItemInterface;
/**
* LockRegistry is used internally by existing adapters to protect against cache stampede.
*
* It does so by wrapping the computation of items in a pool of locks.
* Foreach each apps, there can be at most 20 concurrent processes that
* compute items at the same time and only one per cache-key.
*
* @author Nicolas Grekas <p@tchwork.com>
*/
final class LockRegistry
{
private static $openedFiles = [];
private static $lockedFiles;
private static $signalingException;
private static $signalingCallback;
/**
* The number of items in this list controls the max number of concurrent processes.
*/
private static $files = [
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'AbstractAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'AbstractTagAwareAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'AdapterInterface.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'ApcuAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'ArrayAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'ChainAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'CouchbaseBucketAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'CouchbaseCollectionAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'DoctrineDbalAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'FilesystemAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'FilesystemTagAwareAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'MemcachedAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'NullAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'ParameterNormalizer.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'PdoAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'PhpArrayAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'PhpFilesAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'ProxyAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'Psr16Adapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'RedisAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'RedisTagAwareAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'TagAwareAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'TagAwareAdapterInterface.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'TraceableAdapter.php',
__DIR__.\DIRECTORY_SEPARATOR.'Adapter'.\DIRECTORY_SEPARATOR.'TraceableTagAwareAdapter.php',
];
/**
* Defines a set of existing files that will be used as keys to acquire locks.
*
* @return array The previously defined set of files
*/
public static function setFiles(array $files): array
{
$previousFiles = self::$files;
self::$files = $files;
foreach (self::$openedFiles as $file) {
if ($file) {
flock($file, \LOCK_UN);
fclose($file);
}
}
self::$openedFiles = self::$lockedFiles = [];
return $previousFiles;
}
public static function compute(callable $callback, ItemInterface $item, bool &$save, CacheInterface $pool, \Closure $setMetadata = null, LoggerInterface $logger = null)
{
if ('\\' === \DIRECTORY_SEPARATOR && null === self::$lockedFiles) {
// disable locking on Windows by default
self::$files = self::$lockedFiles = [];
}
$key = self::$files ? abs(crc32($item->getKey())) % \count(self::$files) : -1;
if ($key < 0 || self::$lockedFiles || !$lock = self::open($key)) {
return $callback($item, $save);
}
self::$signalingException ??= unserialize("O:9:\"Exception\":1:{s:16:\"\0Exception\0trace\";a:0:{}}");
self::$signalingCallback ??= function () { throw self::$signalingException; };
while (true) {
try {
$locked = false;
// race to get the lock in non-blocking mode
$locked = flock($lock, \LOCK_EX | \LOCK_NB, $wouldBlock);
if ($locked || !$wouldBlock) {
$logger?->info(sprintf('Lock %s, now computing item "{key}"', $locked ? 'acquired' : 'not supported'), ['key' => $item->getKey()]);
self::$lockedFiles[$key] = true;
$value = $callback($item, $save);
if ($save) {
if ($setMetadata) {
$setMetadata($item);
}
$pool->save($item->set($value));
$save = false;
}
return $value;
}
// if we failed the race, retry locking in blocking mode to wait for the winner
$logger?->info('Item "{key}" is locked, waiting for it to be released', ['key' => $item->getKey()]);
flock($lock, \LOCK_SH);
} finally {
flock($lock, \LOCK_UN);
unset(self::$lockedFiles[$key]);
}
try {
$value = $pool->get($item->getKey(), self::$signalingCallback, 0);
$logger?->info('Item "{key}" retrieved after lock was released', ['key' => $item->getKey()]);
$save = false;
return $value;
} catch (\Exception $e) {
if (self::$signalingException !== $e) {
throw $e;
}
$logger?->info('Item "{key}" not found while lock was released, now retrying', ['key' => $item->getKey()]);
}
}
return null;
}
private static function open(int $key)
{
if (null !== $h = self::$openedFiles[$key] ?? null) {
return $h;
}
set_error_handler(function () {});
try {
$h = fopen(self::$files[$key], 'r+');
} finally {
restore_error_handler();
}
return self::$openedFiles[$key] = $h ?: @fopen(self::$files[$key], 'r');
}
}