Catch exceptions from weakref callbacks

src/gc/collector.cpp

@@ -660,7 +660,12 @@ static void graphTraversalMarking(Worklist& worklist, GCVisitor& visitor) {
 
 static void callWeakrefCallback(PyWeakReference* head) {
     if (head->wr_callback) {
-        runtimeCall(head->wr_callback, ArgPassSpec(1), reinterpret_cast<Box*>(head), NULL, NULL, NULL, NULL);
+        try {
+            runtimeCall(head->wr_callback, ArgPassSpec(1), reinterpret_cast<Box*>(head), NULL, NULL, NULL, NULL);
+        } catch (ExcInfo e) {
+            setCAPIException(e);
+            PyErr_WriteUnraisable(head->wr_callback);
+        }
         head->wr_callback = NULL;
     }
 }

test/tests/finalizer_exception.py

+# Exceptions from finalizers should get caught:
 import sys
 from testing_helpers import test_gc
 
@@ -24,4 +25,27 @@ test_gc(test, 10)
 
 print sorted(strs)
 
-print "done"
+
+
+# Similarly for exceptions from weakref callbacks:
+import weakref
+
+called_callback = False
+def callback(ref):
+    global called_callback
+    if not called_callback:
+        print "callback"
+        called_callback = True
+        raise ValueError()
+
+class C(object):
+    pass
+
+import gc
+l = []
+
+# Make a bunch of them just to make sure at least one gets collected:
+for i in xrange(100):
+    l.append(weakref.ref(C(), callback))
+
+gc.collect()