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From Aki Yoshida <elak...@googlemail.com>
Subject server-side endpoint cleanup problem in spring based CXF scenarios in OSGi
Date Wed, 06 Jul 2011 12:39:16 GMT
Hi,
There seems to be a problem in working with a spring based CXF
server-side endpoint in OSGi that can lead to a serious stability
issue. I would like to bring up this problem here for discussion so
that we can find a solution to it.

We can expect that an endpoint bundle (or a CXF scenario bundle,
whatever you call it) does not get automatically stopped when the cxf
bundle is stopped, if the scenario bundle is configured using spring
instead of blueprint. But whichever configuration is used, the
scenario bundle should be releasing all its resources when it is
stopped while the cxf bundle is already stopped.  However, it appears
to be that some resources are not released in this case. And I have
been thinking about a way to fix this issue. This problem is only
relevant when the cxf-bundle is just stopped without a
uninstall/install cycle.

Basically, what appears to be happening is, when the cxf bundle is
started, it instantiates a DestinationRegistryImpl instance and a
CXFNonSpringServlet servlet instance. And they are exposed as OSGi
services. When a scenario bundle is started, it instantiates an
AbstractHTTPDestination, registers it in the servlet’s destination
registry, and stores additional server-side bookkeeping information in
the CXFBusLifeCycleManager.

When the scenario bundle is stopped, the CXFBusLifeCycleManager
executes a series of cleanup actions which are grouped in the
preShutdown and postShutdown phases. In the preShutdown phase, the
corresponding server instance, ServerImpl, is stopped and this in turn
calls the destination’s (AbstractHTTPDestinations’) shutdown method.
This method accesses the registry object and removes the corresponding
path from it. This registry object is exposed as a proxy to the
scenario bundle and accessible while the cxf-bundle is active. When
the cxf-bundle is no longer active (e.g., stopped before), the thread
accessing this object simply gets blocked and never comes back alive.

Consequently, the clean up code placed in the subsequent phases is not
executed and this prevents some objects such as the bus and endpoint
instances to be released from memory. The destination registry is
probably also in some strange state as it goes stale before getting
emptied. The very bad side of this problem is that you don’t see any
errors in the log nor in the console. You only notice that your
console gets slow after a few start/stop cycles. You can observe the
manifestation of this problem when you use JMX or some analytical
tool.

As I mentioned earlier, I have thought about a way to prevent this
failed clean up step and tried the following approach that seems to
solve this issue.

In short, I added the appropriate cleanup code in the destroy method
of CXFNonSpringServlet and slightly modified AbstractHTTPDestination.
The long version follows.

First of all, the destination registry object is held in
CXFNonSpringServlet. I think this registry can get cleaned up when
this servlet itself is no longer in use (when the cxf-bundle is
stopped and the web container unregisters this servlet). Therefore, I
added in its destroy method the appropriate cleanup code for its
destination registry. And as I needed a way to mark the corresponding
destination (AbstractHTTPDestination) as “done/unregistered” so that
when the scenario bundle is stopped and the destination object is to
be cleaned up, the executing thread does not access the stale registry
reference attached to this destination object, I added method
releaseRegistry() in AbstractHTTPDestnation to set its registry to
null and changed the shutdown method of AbstractHTTPDestination to
accesses the registry reference and uses it only when the registry
reference is not null. With these changes, I am observing that the
scenario bundle can complete its clean up steps even when the
cxf-bundle is already stopped, thereby avoiding the problem described.

I am not sure if there is some problem with this approach or if there
are better approaches. I would appreciate your comments.

Thanks.
Regards, aki

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