BaseOptimizedSessionPersistedObject does not work correctly with Tomcat & Jetty
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Key: TAP5-834
URL: https://issues.apache.org/jira/browse/TAP5-834
Project: Tapestry 5
Issue Type: Bug
Components: tapestry-core
Affects Versions: 5.0.18, 5.1.0.5, 5.1.0.4, 5.1.0.3, 5.1.0.2, 5.1.0.1,
5.1.0.0
Reporter: Andy Blower
Priority: Critical
OptimizedSessionPersistedObject's suggestion for implementing
isSessionPersistedObjectDirty(), as used by
BaseOptimizedSessionPersistedObject, does not work correctly with Tomcat &
Jetty. (and quite possibly other servlet containers too, but we only use Jetty
& Tomcat so have only confirmed it with them)
OptimizedSessionPersistedObject model relies on the servlet container session
object triggering a HttpSessionBindingEvent when an object is re-stored in the
session to reset the dirty flag. I've only looked at the source of Tomcat 5.5
and 6 but when an object is replaced in the session using setAttribute() the
new object and the existing object are compared by reference only, if they both
refer to the same object then no HttpSessionBindingEvent is triggered.
>From Tomcat StandardSession.java:
// Call the valueBound() method if necessary
if (notify && value instanceof HttpSessionBindingListener) {
// Don't call any notification if replacing with the same value
Object oldValue = attributes.get(name);
if (value != oldValue) {
event = new HttpSessionBindingEvent(getSession(), name, value);
try {
((HttpSessionBindingListener) value).valueBound(event);
} catch (Throwable t){
manager.getContainer().getLogger().error
(sm.getString("standardSession.bindingEvent"), t);
}
}
}
So, using OptimizedSessionPersistedObject, there is currently no way of setting
the dirty flag to false after the object has been saved in the session - hence
we are propagating all of the SSOs across the cluster all of the time because
the dirty flag stays set to true.
I think there are two possible solutions to this issue - I prefer the first by
a large margin, but both modify the SessionImpl.restoreDirtyObjects() method.
1) Add a new method to OptimizedSessionPersistedObject interface to reset the
dirty flag, and a corresponding method in SessionPersistedObjectAnalyzer -
implementing them as appropriate, then call the new reset method after setting
the session attribute in SessionImpl.restoreDirtyObjects().
2) Remove the session attribute before adding it in
SessionImpl.restoreDirtyObjects(). Although I have a worry that this may
potentially cause hard to find concurrency problems.
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