Re-use existing ProcessLauncher from wsgi in RPC workers

If both are run under the same process, and api_workers >= 2, the server
process will instantiate two oslo_service.ProcessLauncher instances

This should be avoided [0], and indeed causes issues on subprocess and
signal handling: killed RPC workers not respawning, SIGHUP on master
process leading to unresponsive server, signal not properly sent to all
child processes, ...

To avoid this, use the wsgi ProcessLauncher instance if it exists

[0] https://docs.openstack.org/oslo.service/latest/user/usage.html#launchers

Conflicts:
	neutron/service.py

Depends-On: https://review.opendev.org/708825/
Change-Id: Ic821f8ca84add9c8137ef712031afb43e491591c
Closes-Bug: #1780139
(cherry picked from commit 13aa00026f)

neutron/server/wsgi_eventlet.py

@@ -27,7 +27,7 @@ def eventlet_wsgi_server():
 
 def start_api_and_rpc_workers(neutron_api):
     try:
-        worker_launcher = service.start_all_workers()
+        worker_launcher = service.start_all_workers(neutron_api)
 
         pool = eventlet.GreenPool()
         api_thread = pool.spawn(neutron_api.wait)

neutron/service.py

@@ -217,7 +217,7 @@ class AllServicesNeutronWorker(neutron_worker.BaseWorker):
         self._launcher.restart()
 
 
-def _start_workers(workers):
+def _start_workers(workers, neutron_api=None):
     process_workers = [
         plugin_worker for plugin_worker in workers
         if plugin_worker.worker_process_count > 0
@@ -225,9 +225,14 @@ def _start_workers(workers):
 
     try:
         if process_workers:
-            worker_launcher = common_service.ProcessLauncher(
-                cfg.CONF, wait_interval=1.0
-            )
+            # Get eventual already existing instance from WSGI app
+            worker_launcher = None
+            if neutron_api:
+                worker_launcher = neutron_api.wsgi_app.process_launcher
+            if worker_launcher is None:
+                worker_launcher = common_service.ProcessLauncher(
+                    cfg.CONF, wait_interval=1.0
+                )
 
             # add extra process worker and spawn there all workers with
             # worker_process_count == 0
@@ -259,9 +264,9 @@ def _start_workers(workers):
                           'details.')
 
 
-def start_all_workers():
+def start_all_workers(neutron_api=None):
     workers = _get_rpc_workers() + _get_plugins_workers()
-    launcher = _start_workers(workers)
+    launcher = _start_workers(workers, neutron_api)
     registry.publish(resources.PROCESS, events.AFTER_SPAWN, None)
     return launcher
 

neutron/wsgi.py

@@ -224,6 +224,12 @@ class Server(object):
                              log_format=CONF.wsgi_log_format,
                              socket_timeout=self.client_socket_timeout)
 
+    @property
+    def process_launcher(self):
+        if isinstance(self._server, common_service.ProcessLauncher):
+            return self._server
+        return None
+
 
 class Request(wsgi.Request):