function _apdqc_lock_acquire in Asynchronous Prefetch Database Query Cache 7

Same name in this branch

1. 7 apdqc.lock.apc.inc \_apdqc_lock_acquire()
2. 7 apdqc.lock.db.inc \_apdqc_lock_acquire()
3. 7 apdqc.lock.memcache_storage.inc \_apdqc_lock_acquire()
4. 7 apdqc.lock.memcache.inc \_apdqc_lock_acquire()
5. 7 apdqc.lock.redis.inc \_apdqc_lock_acquire()

Acquire (or renew) a lock, but do not block if it fails.

Parameters

string $name: The name of the lock. Limit of name's length is 255 characters.

float $timeout: A number of seconds (float) before the lock expires (minimum of 0.001).

Return value

bool TRUE if the lock was acquired, FALSE if it failed.

Related topics

1 call to _apdqc_lock_acquire()

apdqc.lock.inc in ./apdqc.lock.inc

A database-mediated implementation of a locking mechanism.

1 string reference to '_apdqc_lock_acquire'

apdqc.lock.inc in ./apdqc.lock.inc

A database-mediated implementation of a locking mechanism.

File

./apdqc.lock.db.inc, line 107

A database-mediated implementation of a locking mechanism.

Code

function _apdqc_lock_acquire($name, $timeout = 30.0) {
  global $locks;

  // Insure that the timeout is at least 1 ms.
  $timeout = max($timeout, 0.001);
  $expire = microtime(TRUE) + $timeout;
  if (isset($locks[$name])) {

    // Build query.
    $query = \Database::getConnection()
      ->prefixTables("\n      UPDATE {" . db_escape_table('semaphore') . "}\n      SET expire = " . (double) $expire . "\n      WHERE name = '" . apdqc_escape_string($name) . "'\n      AND value = '" . apdqc_escape_string(_lock_id()) . "'\n    ");

    // Run Query.
    $results = apdqc_query(array(
      'semaphore',
    ), array(
      $name,
    ), $query, array(
      'get_affected_rows' => TRUE,
    ));
    if (!is_string($results) || $results !== 'NO DB') {
      $success = (bool) $results;
    }
    else {

      // Try to extend the expiration of a lock we already acquired.
      $success = (bool) db_update('semaphore')
        ->fields(array(
        'expire' => $expire,
      ))
        ->condition('name', $name)
        ->condition('value', _lock_id())
        ->execute();
    }
    if (!$success) {

      // The lock was broken.
      unset($locks[$name]);
    }
    return $success;
  }
  else {

    // Optimistically try to acquire the lock, then retry once if it fails.
    // The first time through the loop cannot be a retry.
    $retry = FALSE;

    // We always want to do this code at least once.
    // Build query.
    $query = \Database::getConnection()
      ->prefixTables("\n      INSERT INTO {" . db_escape_table('semaphore') . "}\n      (name, value, expire)\n      VALUES ('" . apdqc_escape_string($name) . "', '" . apdqc_escape_string(_lock_id()) . "', " . (double) $expire . ")\n    ");
    do {

      // Run Query.
      $results = apdqc_query(array(
        'semaphore',
      ), array(
        $name,
      ), $query, array(
        'get_affected_rows' => TRUE,
      ));
      if (!is_string($results) || $results !== 'NO DB') {
        if ($results == 1) {

          // We track all acquired locks in the global variable.
          $locks[$name] = TRUE;

          // We never need to try again.
          $retry = FALSE;
        }
        else {

          // If this is our first pass through the loop, then $retry is FALSE.
          // In this case, the insert must have failed meaning some other
          // request acquired the lock but did not release it. We decide
          // whether to retry by checking lock_may_be_available() Since this
          // will break the lock in case it is expired.
          $retry = $retry ? FALSE : lock_may_be_available($name);
        }
      }
      else {
        try {
          db_insert('semaphore')
            ->fields(array(
            'name' => $name,
            'value' => _lock_id(),
            'expire' => $expire,
          ))
            ->execute();

          // We track all acquired locks in the global variable.
          $locks[$name] = TRUE;

          // We never need to try again.
          $retry = FALSE;
        } catch (PDOException $e) {

          // Suppress the error. If this is our first pass through the loop,
          // then $retry is FALSE. In this case, the insert must have failed
          // meaning some other request acquired the lock but did not release
          // it. We decide whether to retry by checking
          // lock_may_be_available() Since this will break the lock in case it
          // is expired.
          $retry = $retry ? FALSE : lock_may_be_available($name);
        }
      }

      // We only retry in case the first attempt failed, but we then broke
      // an expired lock.
    } while ($retry);
  }
  return isset($locks[$name]);
}