Merge pull request #134 from huazh/subrace

fix race condition in subscription

opcua/common/subscription.py

@@ -272,27 +272,28 @@ class Subscription(object):
         params.ItemsToCreate = monitored_items
         params.TimestampsToReturn = ua.TimestampsToReturn.Neither
 
-        mids = []
+        # insert monitoried item into map to avoid notification arrive before result return
+        # server_handle is left as None in purpose as we don't get it yet.
+        with self._lock:
+            for mi in monitored_items:
+                data = SubscriptionItemData()
+                data.client_handle = mi.RequestedParameters.ClientHandle
+                data.node = Node(self.server, mi.ItemToMonitor.NodeId)
+                data.attribute = mi.ItemToMonitor.AttributeId
+                data.mfilter = mi.RequestedParameters.Filter
+                self._monitoreditems_map[mi.RequestedParameters.ClientHandle] = data
         results = self.server.create_monitored_items(params)
-        # FIXME: Race condition here
-        # We lock as early as possible. But in some situation, a notification may arrives before
-        # locking and we will not be able to prosess it. To avoid issues, users should subscribe
-        # to all nodes at once
+        mids = []
+        # process result, add server_handle, or remove it if failed
         with self._lock:
             for idx, result in enumerate(results):
                 mi = params.ItemsToCreate[idx]
                 if not result.StatusCode.is_good():
+                    del self._monitoreditems_map[mi.RequestedParameters.ClientHandle]
                     mids.append(result.StatusCode)
                     continue
-                data = SubscriptionItemData()
-                data.client_handle = mi.RequestedParameters.ClientHandle
-                data.node = Node(self.server, mi.ItemToMonitor.NodeId)
-                data.attribute = mi.ItemToMonitor.AttributeId
+                data = self._monitoreditems_map[mi.RequestedParameters.ClientHandle]
                 data.server_handle = result.MonitoredItemId
-                #data.mfilter = result.FilterResult
-                data.mfilter = mi.RequestedParameters.Filter
-                self._monitoreditems_map[mi.RequestedParameters.ClientHandle] = data
-
                 mids.append(result.MonitoredItemId)
         return mids