service: don't acquire lock when pool already initialized

mitogen/service.py

@@ -77,20 +77,25 @@ else:
 def get_or_create_pool(size=None, router=None):
     global _pool
     global _pool_pid
+
+    my_pid = os.getpid()
+    if _pool is None or my_pid != _pool_pid:
+        # Avoid acquiring heavily contended lock if possible.
         _pool_lock.acquire()
         try:
-        if _pool_pid != os.getpid():
+            if _pool_pid != my_pid:
                 _pool = Pool(router, [], size=size or DEFAULT_POOL_SIZE,
                              overwrite=True)
                 # In case of Broker shutdown crash, Pool can cause 'zombie'
                 # processes.
                 mitogen.core.listen(router.broker, 'shutdown',
-                                lambda: _pool.stop(join=False))
+                                    lambda: _pool.stop(join=True))
                 _pool_pid = os.getpid()
-        return _pool
         finally:
             _pool_lock.release()
 
+    return _pool
+
 
 def call(service_name, method_name, call_context=None, **kwargs):
     """