quay/util/locking.py

import logging

from redis import RedisError
from redlock import RedLock, RedLockError

from app import app

logger = logging.getLogger(__name__)


class LockNotAcquiredException(Exception):
  """ Exception raised if a GlobalLock could not be acquired. """


class GlobalLock(object):
  """ A lock object that blocks globally via Redis. Note that Redis is not considered a tier-1
      service, so this lock should not be used for any critical code paths.
  """
  def __init__(self, name, lock_ttl=600):
    self._lock_name = name
    self._redis_info = dict(app.config['USER_EVENTS_REDIS'])
    self._redis_info.update({'socket_connect_timeout': 5, 'socket_timeout': 5})

    self._lock_ttl = lock_ttl
    self._redlock = None

  def __enter__(self):
    if not self.acquire():
      raise LockNotAcquiredException()

  def __exit__(self, type, value, traceback):
    self.release()

  def acquire(self):
    logger.debug('Acquiring global lock %s', self._lock_name)
    try:
      redlock = RedLock(self._lock_name, connection_details=[self._redis_info],
                        ttl=self._lock_ttl)
      acquired = redlock.acquire()
      if not acquired:
        logger.debug('Was unable to not acquire lock %s', self._lock_name)
        return False

      self._redlock = redlock
      logger.debug('Acquired lock %s', self._lock_name)
      return True
    except RedLockError:
      logger.debug('Could not acquire lock %s', self._lock_name)
      return False
    except RedisError as re:
      logger.debug('Could not connect to Redis for lock %s: %s', self._lock_name, re)
      return False

  def release(self):
    if self._redlock is not None:
      logger.debug('Releasing lock %s', self._lock_name)
      try:
        self._redlock.release()
      except RedLockError:
        logger.debug('Could not release lock %s', self._lock_name)
      except RedisError as re:
        logger.debug('Could not connect to Redis for releasing lock %s: %s', self._lock_name, re)

      logger.debug('Released lock %s', self._lock_name)
      self._redlock = None