Allow fetching jobboard implementations

To provide a standard way to fetch jobboards
that doesn't require importing the modules themselves
but by using entrypoints instead.

Blueprint jobboard-entrypoints

Change-Id: I13639c6be78a5d003e50e6cfd452c7b810072006

setup.cfg

@@ -36,6 +36,9 @@ packages =
     taskflow
 
 [entry_points]
+taskflow.jobboards =
+    zookeeper = taskflow.jobs.backends.impl_zookeeper:ZookeeperJobBoard
+
 taskflow.persistence =
     dir = taskflow.persistence.backends.impl_dir:DirBackend
     file = taskflow.persistence.backends.impl_dir:DirBackend

taskflow/jobs/backends/__init__.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-#    Copyright (C) 2013 Yahoo! Inc. All Rights Reserved.
+#    Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License"); you may
 #    not use this file except in compliance with the License. You may obtain
@@ -13,3 +13,33 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+
+import logging
+
+import six
+from stevedore import driver
+
+from taskflow import exceptions as exc
+
+
+# NOTE(harlowja): this is the entrypoint namespace, not the module namespace.
+BACKEND_NAMESPACE = 'taskflow.jobboards'
+
+LOG = logging.getLogger(__name__)
+
+
+def fetch(name, conf, namespace=BACKEND_NAMESPACE, **kwargs):
+    # NOTE(harlowja): this allows simpler syntax.
+    if isinstance(conf, six.string_types):
+        conf = {'board': conf}
+
+    board = conf['board']
+    LOG.debug('Looking for %r jobboard driver in %r', board, namespace)
+    try:
+        mgr = driver.DriverManager(namespace, board,
+                                   invoke_on_load=True,
+                                   invoke_args=(name, conf),
+                                   invoke_kwds=kwargs)
+        return mgr.driver
+    except RuntimeError as e:
+        raise exc.NotFound("Could not find jobboard %s" % (board), e)

taskflow/jobs/backends/impl_zookeeper.py

@@ -144,8 +144,7 @@ class ZookeeperJob(base_job.Job):
 
 class ZookeeperJobBoard(jobboard.JobBoard):
     def __init__(self, name, conf, client=None):
-        super(ZookeeperJobBoard, self).__init__(name)
+        super(ZookeeperJobBoard, self).__init__(name, conf)
-        self._conf = conf
         if client is not None:
             self._client = client
             self._owned = False

taskflow/jobs/jobboard.py

@@ -28,8 +28,9 @@ class JobBoard(object):
     capabilities of the underlying jobboard implementation.
     """
 
-    def __init__(self, name):
+    def __init__(self, name, conf):
         self._name = name
+        self._conf = conf
 
     @abc.abstractmethod
     def iterjobs(self, only_unclaimed=False):

taskflow/tests/unit/jobs/test_entrypoint.py

@@ -0,0 +1,49 @@
+# -*- coding: utf-8 -*-
+
+#    Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import contextlib
+
+from zake import fake_client
+
+from taskflow.jobs import backends
+from taskflow.jobs.backends import impl_zookeeper
+from taskflow import test
+
+
+class BackendFetchingTest(test.TestCase):
+    def test_zk_entry_point_text(self):
+        conf = 'zookeeper'
+        with contextlib.closing(backends.fetch('test', conf)) as be:
+            self.assertIsInstance(be, impl_zookeeper.ZookeeperJobBoard)
+
+    def test_zk_entry_point(self):
+        conf = {
+            'board': 'zookeeper',
+        }
+        with contextlib.closing(backends.fetch('test', conf)) as be:
+            self.assertIsInstance(be, impl_zookeeper.ZookeeperJobBoard)
+
+    def test_zk_entry_point_existing_client(self):
+        existing_client = fake_client.FakeClient()
+        conf = {
+            'board': 'zookeeper',
+        }
+        kwargs = {
+            'client': existing_client,
+        }
+        with contextlib.closing(backends.fetch('test', conf, **kwargs)) as be:
+            self.assertIsInstance(be, impl_zookeeper.ZookeeperJobBoard)
+            self.assertIs(existing_client, be._client)