Predis.php in Redis 7

File

lib/Redis/Lock/Backend/Predis.php

<?php

/**
 * Predis lock backend implementation.
 */
class Redis_Lock_Backend_Predis extends Redis_Lock_Backend_Default {
  public function lockAcquire($name, $timeout = 30.0) {
    $client = Redis_Client::getClient();
    $key = 'lock:' . $name;
    $keyOwn = $key . ':owner';
    $id = $this
      ->getLockId();

    // Insure that the timeout is at least 1 second, we cannot do otherwise with
    // Redis, this is a minor change to the function signature, but in real life
    // nobody will notice with so short duration.
    $timeout = ceil(max($timeout, 1));

    // 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.
      $client
        ->watch($keyOwn);

      // 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 ($client
        ->get($keyOwn) != $id) {

        // Explicit UNWATCH we are not going to run the MULTI/EXEC block.
        $client
          ->unwatch($keyOwn);
        unset($this->_locks[$name]);
        return FALSE;
      }
      $replies = $client
        ->pipeline(function ($pipe) use ($key, $keyOwn, $timeout, $id) {
        $pipe
          ->multi();

        // See comment below, there is no guarantee that the lock does not
        // expire while we are actually sending the transaction. At least it
        // really narrow down the actual potential race condition range, but
        // do not remove it.
        $pipe
          ->expire($key, $timeout);
        $pipe
          ->setex($keyOwn, $timeout, $id);
        $pipe
          ->exec();
      });
      $execReply = array_pop($replies);
      if (FALSE === $execReply[1]) {
        unset($this->_locks[$name]);
        return FALSE;
      }
      return TRUE;
    }
    else {
      $client
        ->watch($key);
      $replies = $client
        ->pipeline(function ($pipe) use ($key, $keyOwn, $timeout, $id) {
        $pipe
          ->multi();

        // The INCR command should reset the EXPIRE state, so we are now the
        // official owner. Set the owner flag and real EXPIRE delay.
        $pipe
          ->incr($key);
        $pipe
          ->expire($key, $timeout);
        $pipe
          ->setex($keyOwn, $timeout, $id);
        $pipe
          ->exec();
      });
      $execReply = array_pop($replies);

      // If another client modified the $key value, transaction will be discarded
      // $result will be set to FALSE. This means atomicity have been broken and
      // the other client took the lock instead of us. The another condition is
      // the INCR result test. If we succeeded in incrementing the counter but
      // that counter was more than 0, then someone else already have the lock
      // case in which we cannot proceed.
      // EXPIRE and SETEX won't return something here, EXEC return is index 2.
      // This was determined debugging, seems to be Predis specific.
      if (FALSE === $execReply[2] || 1 != $execReply[0]) {
        return FALSE;
      }

      // Register the lock and return.
      return $this->_locks[$name] = TRUE;
    }
    return FALSE;
  }
  public function lockMayBeAvailable($name) {
    $client = Redis_Client::getClient();
    $key = 'lock:' . $name;
    $id = $this
      ->getLockId();
    list($value, $owner) = $client
      ->mget(array(
      $key,
      $key . ':owner',
    ));
    return empty($value) || $id == $owner;
  }
  public function lockRelease($name) {
    $client = Redis_Client::getClient();
    $key = 'lock:' . $name;
    $keyOwn = $key . ':owner';
    $id = $this
      ->getLockId();
    unset($this->_locks[$name]);

    // FIXME: AFAIK for acquire operation, the mutex is OK, but I'm not sure
    // for this one, it'll need further brainstorming.
    $client
      ->watch($keyOwn);
    if ($client
      ->get($keyOwn == $id)) {
      $client
        ->multi();
      $client
        ->del(array(
        $key,
        $keyOwn,
      ));
      $client
        ->exec();
    }
    else {
      $client
        ->unwatch();
    }
  }
  public function lockReleaseAll($lock_id = NULL) {
    if (!isset($lock_id) && empty($locks)) {
      return;
    }
    $client = Redis_Client::getClient();
    $id = isset($lock_id) ? $lock_id : $this
      ->getLockId();

    // 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) {
      $key = 'lock:' . $name;

      // FIXME: Once again, this is not atomic, see lock_release() documentation.
      $owner = $client
        ->get($key . ':owner');
      if (empty($owner) || $owner == $id) {
        $client
          ->del(array(
          $key,
          $key . ':owner',
        ));
      }
    }
  }

}

Classes

Name	Description
Redis_Lock_Backend_Predis	Predis lock backend implementation.