-
Bug
-
Resolution: Done
-
Minor
-
None
Under some circumstances, the "core" field of a hudson.util.CopyOnWriteMap.Tree instance can be an instance of java.util.Collections.EmptyMap, which is not a subclass of TreeMap. When this happens, the following error is seen during serialization:
2010-02-25 00:43:09,238 ERROR [hudson.model.Executor] Executor throw an exception unexpectedly
java.lang.RuntimeException: Failed to serialize com.example.MyBuild#detailsMap for class com.example.MyBuild
at hudson.util.RobustReflectionConverter$2.writeField(RobustReflectionConverter.java:160)
at hudson.util.RobustReflectionConverter$2.visit(RobustReflectionConverter.java:131)
at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.visitSerializableFields(PureJavaReflectionProvider.java:130)
at hudson.util.RobustReflectionConverter.doMarshal(RobustReflectionConverter.java:116)
at hudson.util.RobustReflectionConverter.marshal(RobustReflectionConverter.java:89)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63)
at com.thoughtworks.xstream.core.TreeMarshaller.start(TreeMarshaller.java:98)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.marshal(AbstractTreeMarshallingStrategy.java:38)
at com.thoughtworks.xstream.XStream.marshal(XStream.java:837)
at com.thoughtworks.xstream.XStream.marshal(XStream.java:826)
at com.thoughtworks.xstream.XStream.toXML(XStream.java:801)
at hudson.XmlFile.write(XmlFile.java:161)
at hudson.model.Run.save(Run.java:1235)
at hudson.model.Run.run(Run.java:1162)
at hudson.model.Build.run(Build.java:74)
at hudson.model.ResourceController.execute(ResourceController.java:93)
at hudson.model.Executor.run(Executor.java:122)
Caused by: java.lang.ClassCastException: java.util.Collections$EmptyMap cannot be cast to java.util.TreeMap
at com.thoughtworks.xstream.converters.collections.TreeMapConverter.marshal(TreeMapConverter.java:50)
at hudson.util.CopyOnWriteMap$Tree$ConverterImpl.marshal(CopyOnWriteMap.java:221)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63)
at hudson.util.RobustReflectionConverter.marshallField(RobustReflectionConverter.java:168)
at hudson.util.RobustReflectionConverter$2.writeField(RobustReflectionConverter.java:156)
... 18 more
It looks like this can happen either when the Tree() or Tree(Comparator) constructors are called or when clear() is called. In those cases, if you don't add any elements, you'll get the wrong kind of map in the core and serialization will fail. The one case that should work is if you do putAll() with an empty Map after creation; that will successfully replace the core with a TreeMap.
I've attached a proposed patch. It adds an emptyMap() method to CopyOnWriteMap that is implemented by the two subclasses. All calls that previously went to Collections.emptyMap() now let the subclass decide what type of map to return. It also adds a test for serializing an empty CopyOnWriteMap.Tree. This patch takes the naive approach of creating a new TreeMap every time that emptyMap() is called. It may or not be worthwhile to try to reuse a TreeMap instance for this purpose since CopyOnWriteMap guarantees that the core itself won't be updated.
