Source code for inspirehep.utils.lock

# -*- coding: utf-8 -*-
#
# This file is part of INSPIRE.
# Copyright (C) 2018 CERN.
#
# INSPIRE is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# INSPIRE is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with INSPIRE. If not, see <http://www.gnu.org/licenses/>.
#
# In applying this license, CERN does not waive the privileges and immunities
# granted to it by virtue of its status as an Intergovernmental Organization
# or submit itself to any jurisdiction.

"""Locking."""

from __future__ import absolute_import, division, print_function

from contextlib import contextmanager

from flask import current_app as app
from redis import StrictRedis
from redis_lock import Lock


@contextmanager
def distributed_lock(lock_name, expire=10, auto_renewal=True, blocking=False):
    """Context manager to acquire a lock visible by all processes.

    This lock is implemented through Redis in order to be globally visible.

    Args:
        lock_name (str): name of the lock to be acquired.
        expire (int): duration in seconds after which the lock is released if
            not renewed in the meantime.
        auto_renewal (bool): if ``True``, the lock is automatically renewed as long
            as the context manager is still active.
        blocking (bool): if ``True``, wait for the lock to be released. If ``False``,
            return immediately, raising :class:`DistributedLockError`.

    It is recommended to set ``expire`` to a small value and
    ``auto_renewal=True``, which ensures the lock gets released quickly in case
    the process is killed without limiting the time that can be spent holding
    the lock.

    Raises:
        DistributedLockError: when ``blocking`` is set to ``False`` and the lock is already acquired.
    """
    if not lock_name:
        raise ValueError('Lock name not specified.')

    redis_url = app.config.get('CACHE_REDIS_URL')

    redis = StrictRedis.from_url(redis_url)
    lock = Lock(redis, lock_name, expire=expire, auto_renewal=auto_renewal)

    if lock.acquire(blocking=blocking):
        try:
            yield
        finally:
            lock.release()
    else:
        raise DistributedLockError('Cannot acquire lock for %s', lock_name)


class DistributedLockError(Exception):
    pass