PhpRedis.php in Redis 8

Namespace

Drupal\redis\Lock

File

src/Lock/PhpRedis.php

<?php

namespace Drupal\redis\Lock;

use Drupal\Core\Lock\LockBackendAbstract;
use Drupal\redis\ClientFactory;
use Drupal\redis\RedisPrefixTrait;

/**
 * Predis lock backend implementation.
 */
class PhpRedis extends LockBackendAbstract {
  use RedisPrefixTrait;

  /**
   * @var \Redis
   */
  protected $client;

  /**
   * Creates a PHpRedis cache backend.
   */
  public function __construct(ClientFactory $factory) {
    $this->client = $factory
      ->getClient();

    // __destruct() is causing problems with garbage collections, register a
    // shutdown function instead.
    drupal_register_shutdown_function([
      $this,
      'releaseAll',
    ]);
  }

  /**
   * Generate a redis key name for the current lock name.
   *
   * @param string $name
   *   Lock name.
   *
   * @return string
   *   The redis key for the given lock.
   */
  protected function getKey($name) {
    return $this
      ->getPrefix() . ':lock:' . $name;
  }

  /**
   * {@inheritdoc}
   */
  public function acquire($name, $timeout = 30.0) {
    $key = $this
      ->getKey($name);
    $id = $this
      ->getLockId();

    // Insure that the timeout is at least 1 ms.
    $timeout = max($timeout, 0.001);

    // If we already have the lock, check for his owner and attempt a new EXPIRE
    // command on it.
    if (isset($this->locks[$name])) {

      // Create a new transaction, for atomicity.
      $this->client
        ->watch($key);

      // Global tells us we are the owner, but in real life it could have expired
      // and another process could have taken it, check that.
      if ($this->client
        ->get($key) != $id) {

        // Explicit UNWATCH we are not going to run the MULTI/EXEC block.
        $this->client
          ->unwatch();
        unset($this->locks[$name]);
        return FALSE;
      }
      $result = $this->client
        ->multi()
        ->psetex($key, (int) ($timeout * 1000), $id)
        ->exec();

      // If the set failed, someone else wrote the key, we failed to acquire
      // the lock.
      if (FALSE === $result) {
        unset($this->locks[$name]);

        // Explicit transaction release which also frees the WATCH'ed key.
        $this->client
          ->discard();
        return FALSE;
      }
      return $this->locks[$name] = TRUE;
    }
    else {

      // Use a SET with microsecond expiration and the NX flag, which will only
      // succeed if the key does not exist yet.
      $result = $this->client
        ->set($key, $id, [
        'nx',
        'px' => (int) ($timeout * 1000),
      ]);

      // If the result is FALSE, we failed to acquire the lock.
      if (FALSE === $result) {
        return FALSE;
      }

      // Register the lock.
      return $this->locks[$name] = TRUE;
    }
  }

  /**
   * {@inheritdoc}
   */
  public function lockMayBeAvailable($name) {
    $key = $this
      ->getKey($name);
    $value = $this->client
      ->get($key);
    return $value === FALSE || $value === NULL;
  }

  /**
   * {@inheritdoc}
   */
  public function release($name) {
    $key = $this
      ->getKey($name);
    $id = $this
      ->getLockId();
    unset($this->locks[$name]);

    // Ensure the lock deletion is an atomic transaction. If another thread
    // manages to removes all lock, we can not alter it anymore else we will
    // release the lock for the other thread and cause race conditions.
    $this->client
      ->watch($key);
    if ($this->client
      ->get($key) == $id) {
      $this->client
        ->multi();
      $this->client
        ->del($key);
      $this->client
        ->exec();
    }
    else {
      $this->client
        ->unwatch();
    }
  }

  /**
   * {@inheritdoc}
   */
  public function releaseAll($lock_id = NULL) {

    // We can afford to deal with a slow algorithm here, this should not happen
    // on normal run because we should have removed manually all our locks.
    foreach ($this->locks as $name => $foo) {
      $this
        ->release($name);
    }
  }

}

Classes

Name	Description
PhpRedis	Predis lock backend implementation.