Use Redis for locking

Replace django-db-locking with Redis locks. This removes a dependency on
the former, but adds one on the latter.

README.rst

@@ -25,6 +25,9 @@ How to install:
         'smsgateway.backends.smsextrapro.SmsExtraProBackend',
     )
 
+    # The Redis used for locking the tasks
+    SMSGATEWAY_REDIS_URL = ''
+
 * Some backends support incoming text messages:
 
     # urls.py
@@ -35,4 +38,4 @@ How to install:
         (r'^incoming_sms/$', backends.get_backend('mobileweb').handle_incoming),
     )
 
-* Set up your SMS gateway to use this url for incoming messages.
+* Set up your SMS gateway to use this url for incoming messages.

requirements/requirements.txt

@@ -3,16 +3,14 @@ Django>=2.1.5
 django-statsd-unleashed>=1.0.1
 statsd>=2.1.2
 
-redis>=2.10.5
+redis>=3.0.0
 celery==4.0.2
 kombu==4.0.2
 billiard==3.5.0.2
 amqp==2.1.4
 vine==1.1.3
 pytz>=2016.7
 
-django-db-locking>=2.0.0
-
 phonenumberslite==7.3.2
 
 six>=1.11.0,<2.0

smsgateway/__init__.py

@@ -1,5 +1,5 @@
 from __future__ import absolute_import
-__version__ = '2.1.21'
+__version__ = '2.2.0'
 
 
 def get_account(using=None):

smsgateway/tasks.py

@@ -2,13 +2,13 @@
 from datetime import datetime
 from logging import getLogger
 from redis import ConnectionPool, Redis
+from redis.lock import Lock
 from waffle.models import Switch
 
 from django.conf import settings
 from celery import shared_task
 from celery.utils.log import get_task_logger
 from django_statsd.clients import statsd
-from locking.models import NonBlockingLock
 
 from smsgateway import get_account, send, send_queued
 from smsgateway.backends.base import SMSBackend
@@ -41,7 +41,8 @@ def _send_smses(send_deferred=False, backend=None, limit=None):
     else:
         send_lock_name = 'smsgateway_send_sms'
 
-    with NonBlockingLock.objects.acquire_lock(lock_name=send_lock_name):
+    with Lock(redis=Redis.from_url(settings.SMSGATEWAY_REDIS_URL), name='smsgateway-' + send_lock_name,
+              blocking_timeout=0):
         successes, failures = 0, 0
         try:
             # Get SMSes that need to be sent (deferred or non-deferred)