Check dnsmasq process is active when spawned

After spawning the "dnsmasq" process in the method
"Dnsmasq._spawn_or_reload_process", we need to check that the "dnsmasq"
process is running and could be detected by the ProcessManager instance
controlling it.

ProcessManager determines if a process is "active":
- If the network ID is in the cmdline used to execute the process.
- If the process is detected by psutil.Process(pid), returning the
  cmdline needed in the first condition.
- If the PID file exists; this is written by the dnsmasq process
  once is started and is needed in the second condition.

To make this feature available for any other process using
ProcessManager, the implementation is done in this class.

Change-Id: I51dc9d342c613afcbcfdc50a1d2811502748f170
Closes-Bug: #1849502
(cherry picked from commit 7c5ce50a0c)

neutron/agent/linux/dhcp.py

@@ -467,7 +467,7 @@ class Dnsmasq(DhcpLocalProcess):
         pm = self._get_process_manager(
             cmd_callback=self._build_cmdline_callback)
 
-        pm.enable(reload_cfg=reload_with_HUP)
+        pm.enable(reload_cfg=reload_with_HUP, ensure_active=True)
 
         self.process_monitor.register(uuid=self.network.id,
                                       service_name=DNSMASQ_SERVICE_NAME,

neutron/agent/linux/external_process.py

@@ -26,6 +26,7 @@ import six
 
 from neutron.agent.linux import ip_lib
 from neutron.agent.linux import utils
+from neutron.common import utils as common_utils
 from neutron.conf.agent import common as agent_cfg
 
 
@@ -78,7 +79,7 @@ class ProcessManager(MonitoredProcess):
         fileutils.ensure_tree(os.path.dirname(self.get_pid_file_name()),
                               mode=0o755)
 
-    def enable(self, cmd_callback=None, reload_cfg=False):
+    def enable(self, cmd_callback=None, reload_cfg=False, ensure_active=False):
         if not self.active:
             if not cmd_callback:
                 cmd_callback = self.default_cmd_callback
@@ -89,6 +90,8 @@ class ProcessManager(MonitoredProcess):
                                      run_as_root=self.run_as_root)
         elif reload_cfg:
             self.reload_cfg()
+        if ensure_active:
+            common_utils.wait_until_true(lambda: self.active)
 
     def reload_cfg(self):
         if self.custom_reload_callback:

neutron/tests/unit/agent/linux/test_dhcp.py

@@ -1343,7 +1343,7 @@ class TestDnsmasq(TestBase):
 
             self.assertTrue(test_pm.register.called)
             self.external_process().enable.assert_called_once_with(
-                reload_cfg=False)
+                ensure_active=True, reload_cfg=False)
             call_kwargs = self.external_process.mock_calls[0][2]
             cmd_callback = call_kwargs['default_cmd_callback']
 
@@ -2108,7 +2108,7 @@ class TestDnsmasq(TestBase):
         dm.reload_allocations()
         self.assertTrue(test_pm.register.called)
         self.external_process().enable.assert_called_once_with(
-            reload_cfg=True)
+            ensure_active=True, reload_cfg=True)
 
         self.safe.assert_has_calls([
             mock.call(exp_host_name, exp_host_data),

neutron/tests/unit/agent/linux/test_external_process.py

@@ -21,6 +21,7 @@ from oslo_utils import fileutils
 import psutil
 
 from neutron.agent.linux import external_process as ep
+from neutron.common import utils as common_utils
 from neutron.tests import base
 
 
@@ -169,6 +170,24 @@ class TestProcessManager(base.BaseTestCase):
                 manager.enable(callback)
                 self.assertFalse(callback.called)
 
+    def test_enable_with_ensure_active(self):
+        def _create_cmd(*args):
+            return ['sleep', 0]
+
+        pm = ep.ProcessManager(self.conf, 'uuid', pid_file='pid_file',
+                               default_cmd_callback=_create_cmd)
+        with mock.patch.object(psutil, 'Process') as mock_psutil_process, \
+                mock.patch.object(ep.ProcessManager, 'pid',
+                                  new_callable=mock.PropertyMock) as mock_pid:
+            mock_pid.return_value = 'pid_value'
+            mock_process = mock.Mock()
+            mock_process.cmdline.side_effect = [[], ['the', 'cmd', 'uuid']]
+            mock_psutil_process.return_value = mock_process
+            try:
+                pm.enable(ensure_active=True)
+            except common_utils.WaitTimeout:
+                self.fail('ProcessManager.enable() raised WaitTimeout')
+
     def test_reload_cfg_without_custom_reload_callback(self):
         with mock.patch.object(ep.ProcessManager, 'disable') as disable:
             manager = ep.ProcessManager(self.conf, 'uuid', namespace='ns')