Add Redis based distributed lock backend

- RedisLock backend requires one argument: "redis_url".
  Example: redis://127.0.0.1:6379/0

- Add the setting LOCK_MANAGER_BACKEND_ARGUMENTS.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -169,6 +169,9 @@
 - Add document type change API endpoint.
 - Change OCR API submit URL from documents/{pk}/submit
   to documents/{pk}/ocr/submit.
+- Add Redis based distributed lock backend. Requires one
+  argument: "redis_url". Example: redis://127.0.0.1:6379/0
+- Add the setting LOCK_MANAGER_BACKEND_ARGUMENTS.
 
 3.3.11 (2019-XX-XX)
 ===================

mayan/apps/lock_manager/backends/redis_lock.py

@@ -0,0 +1,43 @@
+from __future__ import unicode_literals
+
+import redis
+
+from ..exceptions import LockError
+from ..settings import setting_backend_arguments
+
+from .base import LockingBackend
+
+
+class RedisLock(LockingBackend):
+    @classmethod
+    def acquire_lock(cls, name, timeout=None):
+        super(RedisLock, cls).acquire_lock(name=name, timeout=timeout)
+        return RedisLock(name=name, timeout=timeout)
+
+    @classmethod
+    def get_redis_connection(cls):
+        redis_url = setting_backend_arguments.value.get('redis_url', None)
+        server = redis.from_url(url=redis_url)
+        server.client_id()
+        return server
+
+    @classmethod
+    def purge_locks(cls):
+        super(RedisLock, cls).purge_locks()
+
+    def __init__(self, name, timeout):
+        self.name = name
+        redis_lock_instance = self.get_redis_connection().lock(
+            name=name, timeout=timeout, sleep=0.1, blocking_timeout=0.1
+        )
+        if redis_lock_instance.acquire():
+            self.redis_lock_instance = redis_lock_instance
+        else:
+            raise LockError
+
+    def release(self):
+        super(RedisLock, self).release()
+        try:
+            self.redis_lock_instance.release()
+        except redis.exceptions.LockNotOwnedError:
+            return

mayan/apps/lock_manager/settings.py

@@ -15,6 +15,10 @@ setting_backend = namespace.add_setting(
         'resource locks.'
     )
 )
+setting_backend_arguments = namespace.add_setting(
+    global_name='LOCK_MANAGER_BACKEND_ARGUMENTS',
+    default={}, help_text=_('Arguments to pass to the LOCK_MANAGER_BACKEND.')
+)
 
 setting_default_lock_timeout = namespace.add_setting(
     default=DEFAULT_LOCK_TIMEOUT_VALUE,

mayan/apps/lock_manager/tests/test_backends.py

@@ -2,18 +2,21 @@ from __future__ import unicode_literals
 
 import time
 
-from django.test import TestCase
+from django.test import override_settings
 from django.utils.module_loading import import_string
 
+from mayan.apps.common.tests.base import BaseTestCase
+
 from ..exceptions import LockError
 
 TEST_LOCK_1 = 'test lock 1'
 
 
-class FileLockTestCase(TestCase):
+class FileLockTestCase(BaseTestCase):
     backend_string = 'mayan.apps.lock_manager.backends.file_lock.FileLock'
 
     def setUp(self):
+        super(FileLockTestCase, self).setUp()
         self.locking_backend = import_string(self.backend_string)
 
     def test_exclusive(self):
@@ -72,3 +75,10 @@ class FileLockTestCase(TestCase):
 
 class ModelLockTestCase(FileLockTestCase):
     backend_string = 'mayan.apps.lock_manager.backends.model_lock.ModelLock'
+
+
+@override_settings(
+    LOCK_MANAGER_BACKEND_ARGUMENTS={'redis_url': 'redis://127.0.0.1:6379/0'}
+)
+class RedisLockTestCase(FileLockTestCase):
+    backend_string = 'mayan.apps.lock_manager.backends.redis_lock.RedisLock'