Changeset 60e401c in trunk

Timestamp:

2020-12-16T21:19:33Z (4 years ago)

Author:

Jean-Paul Calderone <exarkun@…>

Branches:

master

Children:

b2c9296

Parents:

3513e9b

Message:

Make ObserverList? synchronous, reentrant, and exception safe

with tests

Location:

src/allmydata

Files:

• test/test_observer.py (modified) (1 diff)
• util/observer.py (modified) (3 diffs)

src/allmydata/test/test_observer.py ¶

@@ -102 +102 @@
         d.addCallback(_check2)
         return d
+
+    def test_observer_list_reentrant(self):
+        """
+        ``ObserverList`` is reentrant.
+        """
+        observed = []
+
+        def observer_one():
+            obs.unsubscribe(observer_one)
+
+        def observer_two():
+            observed.append(None)
+
+        obs = observer.ObserverList()
+        obs.subscribe(observer_one)
+        obs.subscribe(observer_two)
+        obs.notify()
+
+        self.assertEqual([None], observed)
+
+    def test_observer_list_observer_errors(self):
+        """
+        An error in an earlier observer does not prevent notification from being
+        delivered to a later observer.
+        """
+        observed = []
+
+        def observer_one():
+            raise Exception("Some problem here")
+
+        def observer_two():
+            observed.append(None)
+
+        obs = observer.ObserverList()
+        obs.subscribe(observer_one)
+        obs.subscribe(observer_two)
+        obs.notify()
+
+        self.assertEqual([None], observed)
+        self.assertEqual(1, len(self.flushLoggedErrors(Exception)))

src/allmydata/util/observer.py ¶

@@ -17 +17 @@
 from twisted.internet import defer
 from foolscap.api import eventually
+from twisted.logger import (
+    Logger,
+)
 
 """The idiom we use is for the observed object to offer a method named
@@ -98 +101 @@
 
 class ObserverList(object):
-    """A simple class to distribute events to a number of subscribers."""
+    """
+    Immediately distribute events to a number of subscribers.
+    """
+    _logger = Logger()
 
     def __init__(self):
@@ -110 +116 @@
 
     def notify(self, *args, **kwargs):
-        for o in self._watchers:
-            eventually(o, *args, **kwargs)
+        for o in self._watchers[:]:
+            try:
+                o(*args, **kwargs)
+            except:
+                self._logger.failure("While notifying {o!r}", o=o)
 
 class EventStreamObserver(object):