AttributeSource holds strong reference to class instances and prevents
unloading e.g. in Solr if webapplication reload and custom attributes in
separate classloaders are used (e.g. in the Solr plugins classloader)
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Key: LUCENE-2260
URL: https://issues.apache.org/jira/browse/LUCENE-2260
Project: Lucene - Java
Issue Type: Bug
Affects Versions: 3.0, 2.9.1
Reporter: Uwe Schindler
Assignee: Uwe Schindler
Fix For: 2.9.2, 3.0.1, 3.1
When working on the dynmaic proxy classes using cglib/javaassist i recognized a
problem in the caching code inside AttributeSource:
- AttributeSource has a static (!) cache map that holds implementation classes
for attributes to be faster on creating new attributes (reflection cost)
- AttributeSource has a static (!) cache map that holds a list of all
interfaces implemented by a specific AttributeImpl
Also:
- VirtualMethod in 3.1 hold a map of implementation distances keyed by
subclasses of the deprecated API
Both have the problem that this strong reference is inside Lucene's classloader
and so persists as long as lucene lives. The classes referenced can never be
unloaded therefore, which would be fine if all live in the same classloader. As
soon as the Attribute or implementation class or the subclass of the deprecated
API are loaded by a different classloder (e.g. Lucene lives in bootclasspath of
tomcat, but lucene-consumer with custom attributes lives in a webapp), they can
never be unloaded, because a reference exists.
Libs like CGLIB or JavaAssist or JDK's reflect.Proxy have a similar cache for
generated class files. They also manage this by a WeakHashMap. The cache will
always work perfect and no class will be evicted without reason, as classes are
only unloaded when the classloader goes and this will only happen on request
(e.g. by Tomcat).
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