Do not fork compute workers in native threading mode

Force running the Compute Service within the main Process with native
threading to keep the baseline behavior.

In eventlet mode with workers=1 or workers=None it is oslo.service's
default behavior[1]. But with native threading we need to explicitly
pass no_fork=True to oslo to get this behavior instead of forking a
single worker [2].

Forking a single worker for compute would also be problematic as compute
initializes the conductor RPC client before such fork and the rabbitmq
oslo.messaging driver does not support forking with a connected client
[3].

Patch bumps the minimum oslo.service version to 4.4.1 to pick up the fix
https://review.opendev.org/c/openstack/oslo.service/+/966458 nova now
depends on.

[1] https://github.com/openstack/oslo.service/blob/37b90521ea01baa0c8e6412453c42972a28e3b12/oslo_service/backend/_eventlet/service.py#L749C1-L753
[2] https://github.com/openstack/oslo.service/blob/37b90521ea01baa0c8e6412453c42972a28e3b12/oslo_service/backend/_threading/service.py#L296-L300
[3] https://docs.openstack.org/oslo.messaging/latest/reference/transport.html#forking-processes-and-oslo-messaging-transport-objects

Change-Id: If6daffc25d737f53b1a478d42fd85a0446b09e6d
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

nova/cmd/compute.py

@@ -61,5 +61,6 @@ def main():
     objects.Service.enable_min_version_cache()
     server = service.Service.create(binary='nova-compute',
                                     topic=compute_rpcapi.RPC_TOPIC)
-    service.serve(server)
+    # Compute service should never fork worker processes
+    service.serve(server, workers=1, no_fork=True)
     service.wait()

nova/service.py

@@ -322,13 +322,13 @@ class Service(service.Service):
 _launcher = None
 
 
-def serve(server, workers=None):
+def serve(server, workers=None, no_fork=False):
     global _launcher
     if _launcher:
         raise RuntimeError(_('serve() can only be called once'))
 
     _launcher = service.launch(CONF, server, workers=workers,
-                               restart_method='mutate')
+                               restart_method='mutate', no_fork=no_fork)
 
 
 def wait():

nova/tests/unit/test_service.py

@@ -324,7 +324,8 @@ class TestLauncher(test.NoDBTestCase):
         mock_launch.assert_called_once_with(mock.ANY,
                                             mock.sentinel.service,
                                             workers=None,
-                                            restart_method='mutate')
+                                            restart_method='mutate',
+                                            no_fork=False)
 
     @mock.patch.object(_service, 'launch')
     def test_launch_app_with_workers(self, mock_launch):
@@ -333,7 +334,19 @@ class TestLauncher(test.NoDBTestCase):
         mock_launch.assert_called_once_with(mock.ANY,
                                             mock.sentinel.service,
                                             workers=mock.sentinel.workers,
-                                            restart_method='mutate')
+                                            restart_method='mutate',
+                                            no_fork=False)
+
+    @mock.patch.object(_service, 'launch')
+    def test_launch_app_with_workers_no_fork(self, mock_launch):
+        service._launcher = None
+        service.serve(
+            mock.sentinel.service, workers=mock.sentinel.workers, no_fork=True)
+        mock_launch.assert_called_once_with(mock.ANY,
+                                            mock.sentinel.service,
+                                            workers=mock.sentinel.workers,
+                                            restart_method='mutate',
+                                            no_fork=True)
 
     @mock.patch.object(_service, 'launch')
     def test_launch_app_more_than_once_raises(self, mock_launch):

requirements.txt

@@ -43,7 +43,7 @@ oslo.messaging>=14.1.0 # Apache-2.0
 oslo.policy>=4.5.0 # Apache-2.0
 oslo.privsep>=2.6.2 # Apache-2.0
 oslo.i18n>=5.1.0 # Apache-2.0
-oslo.service[threading]>=4.2.0 # Apache-2.0
+oslo.service[threading]>=4.4.1 # Apache-2.0
 rfc3986>=1.2.0 # Apache-2.0
 oslo.middleware>=3.31.0 # Apache-2.0
 psutil>=3.2.2 # BSD