Revert "service: replace eventlet event by threading"

This reverts commit f08f6ba7e80729fb6028b24568da0f651a75fcd6.

This was a terrible idea: as soon as you don't monkey patch threading,
this does not work as expected in the end.

So it's better to say that it's explicitly eventlet mechanisms that are
required, at least for now.

Conflicts:
	tests/unit/test_service.py

Partial-Bug: #1274044

Change-Id: I4d4f112d4550d912c4f81e62bc9a4714cf117384

openstack/common/service.py

@@ -23,7 +23,6 @@ import os
 import random
 import signal
 import sys
-import threading
 import time
 
 try:
@@ -35,6 +34,7 @@ except ImportError:
     UnsupportedOperation = None
 
 import eventlet
+from eventlet import event
 from oslo.config import cfg
 
 from openstack.common import eventlet_backdoor
@@ -419,10 +419,11 @@ class Service(object):
         self.tg = threadgroup.ThreadGroup(threads)
 
         # signal that the service is done shutting itself down:
-        self._done = threading.Event()
+        self._done = event.Event()
 
     def reset(self):
-        self._done = threading.Event()
+        # NOTE(Fengqian): docs for Event.reset() recommend against using it
+        self._done = event.Event()
 
     def start(self):
         pass
@@ -431,7 +432,8 @@ class Service(object):
         self.tg.stop()
         self.tg.wait()
         # Signal that service cleanup is done:
-        self._done.set()
+        if not self._done.ready():
+            self._done.send()
 
     def wait(self):
         self._done.wait()
@@ -442,7 +444,7 @@ class Services(object):
     def __init__(self):
         self.services = []
         self.tg = threadgroup.ThreadGroup()
-        self.done = threading.Event()
+        self.done = event.Event()
 
     def add(self, service):
         self.services.append(service)
@@ -456,7 +458,8 @@ class Services(object):
 
         # Each service has performed cleanup, now signal that the run_service
         # wrapper threads can now die:
-        self.done.set()
+        if not self.done.ready():
+            self.done.send()
 
         # reap threads:
         self.tg.stop()
@@ -466,7 +469,7 @@ class Services(object):
 
     def restart(self):
         self.stop()
-        self.done = threading.Event()
+        self.done = event.Event()
         for restart_service in self.services:
             restart_service.reset()
             self.tg.add_thread(self.run_service, restart_service, self.done)

tests/unit/test_service.py

@@ -25,11 +25,11 @@ import multiprocessing
 import os
 import signal
 import socket
-import threading
 import time
 import traceback
 
 import eventlet
+from eventlet import event
 import mock
 import mox
 
@@ -274,11 +274,11 @@ class ServiceRestartTest(ServiceTestBase):
 class _Service(service.Service):
     def __init__(self):
         super(_Service, self).__init__()
-        self.init = threading.Event()
+        self.init = event.Event()
         self.cleaned_up = False
 
     def start(self):
-        self.init.set()
+        self.init.send()
 
     def stop(self):
         self.cleaned_up = True
@@ -358,7 +358,7 @@ class LauncherTest(test.BaseTestCase):
 
         launcher.stop()
         self.assertTrue(svc.cleaned_up)
-        self.assertTrue(svc._done.is_set())
+        self.assertTrue(svc._done.ready())
 
         # make sure stop can be called more than once.  (i.e. play nice with
         # unit test fixtures in nova bug #1199315)