tacker-conductor with oslo.service threading

Move the tacker-conductor entry point out of `tacker.cmd.eventlet` and
select the oslo.service threading backend via `init_backend()` instead
of monkey patching the process. `oslo.service` components used by the
conductor (loopingcall, periodic_task, service.launch) are resolved
through the backend, so they switch to native threads without code
changes.

The deprecated executor argument of `get_rpc_server()` is dropped:
oslo.messaging auto-detects the executor, choosing `eventlet` when
the process is monkey patched (tacker-server) and `threading`
otherwise (tacker-conductor).

The threading backend of `oslo.service` requires the cotyledon and
futurist extras, so the requirement is bumped to
oslo.service[threading]>=4.6.0.

Guard the `init_backend()` call with `get_backend_type() is None` so
that importing this module after `tacker.cmd.eventlet` in the same
process does not raise BackendAlreadySelected. This happens when
Sphinx apidoc imports every module under tacker/ in a single process
to build the docs.

Add pyproject.toml since openstack/requirements
project-requirements-change.py check now requires master-branch
projects to declare their build backend via pyproject.toml,
following pbr 6.x's move to PEP 517 builds.

Depends-On: I984006c155c4f18d005611dcb7b002d1c2fb355d
Signed-off-by: Yasufumi Ogawa <yasufum.o@gmail.com>
Change-Id: Ib8d82141314e931a7e7af0ea3cb686093e2d5f4e

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["pbr>=6.0.0", "setuptools>=64.0.0"]
+build-backend = "pbr.build"

requirements.txt

@@ -30,7 +30,7 @@ oslo.middleware>=3.31.0 # Apache-2.0
 oslo.policy>=4.5.0 # Apache-2.0
 oslo.reports>=1.18.0 # Apache-2.0
 oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
-oslo.service>=2.5.0 # Apache-2.0
+oslo.service[threading]>=4.6.0 # Apache-2.0
 oslo.upgradecheck>=1.3.0 # Apache-2.0
 oslo.utils>=7.0.0 # Apache-2.0
 oslo.versionedobjects>=1.33.3 # Apache-2.0

setup.cfg

@@ -38,7 +38,7 @@ setup-hooks =
 console_scripts =
     tacker-db-manage = tacker.db.migration.cli:main
     tacker-server = tacker.cmd.eventlet.tacker_server:main
-    tacker-conductor = tacker.cmd.eventlet.conductor:main
+    tacker-conductor = tacker.cmd.conductor:main
     tacker-status = tacker.cmd.status:main
 tacker.service_plugins =
     dummy = tacker.tests.unit.dummy_plugin:DummyServicePlugin

tacker/cmd/conductor.py

@@ -10,8 +10,19 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from tacker.conductor import conductor_server
-from tacker import objects
+# NOTE: init_backend() can be called only once per process and must run
+# before any other oslo.service module is imported, otherwise the default
+# eventlet backend is selected implicitly. The get_backend_type() guard
+# avoids BackendAlreadySelected when this module is imported alongside
+# tacker.cmd.eventlet in the same process, e.g. by Sphinx autodoc during
+# the docs build.
+from oslo_service import backend
+
+if backend.get_backend_type() is None:
+    backend.init_backend(backend.BackendType.THREADING)
+
+from tacker.conductor import conductor_server  # noqa: E402
+from tacker import objects  # noqa: E402
 
 
 def main():

tacker/common/rpc.py

@@ -206,8 +206,11 @@ def get_server(target, endpoints, serializer=None):
     assert TRANSPORT is not None
     serializer = RequestContextSerializer(serializer)
     access_policy = dispatcher.DefaultRPCAccessPolicy
+    # NOTE: The executor is auto-detected by oslo.messaging: 'eventlet'
+    # when the process is monkey patched (tacker-server), 'threading'
+    # otherwise (tacker-conductor).
     return oslo_messaging.get_rpc_server(TRANSPORT, target, endpoints,
-                                         'eventlet', serializer,
+                                         serializer=serializer,
                                          access_policy=access_policy)