Re: [equinox-dev] problem with ServiceTracker.open() and refreshThread i

[BJ Hargrave <hargrave@xxxxxxxxxx>]

Yes, open a bug Tim. I can see that a fix
is needed here.
--

BJ Hargrave Senior Technical Staff Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargrave@xxxxxxxxxx

office: +1 386 848 1781 mobile: +1 386 848 3788

From:	Tim Diekmann <tdiekman@xxxxxxxxx>
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:	2010/01/29 22:46
Subject:	[equinox-dev] problem with ServiceTracker.open() and refreshThread        in Equinox
Sent by:	equinox-dev-bounces@xxxxxxxxxxx

---

I ran into a problem with Equinox 3.5.1.R35x_v20090806:

In my log file I find the following exception stack trace
after calling PackageAdmin.refreshPackages(null).

org.osgi.framework.BundleException: Exception in com.tibco.xxx.Activator.start()
of bundle com.tibco.xxx.
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:805)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.start(BundleContextImpl.java:754)
at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(BundleHost.java:352)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:280)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:272)
at com.tibco.xxx.refreshRuntime(xxx.java:872)
at com.tibco.xx.access$6(xxxImpl.java:569)
at com.tibco.xxx$2.run(xxxImpl.java:229)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.IllegalStateException: The service
has been unregistered
at org.eclipse.osgi.internal.serviceregistry.ServiceRegistrationImpl.getReferenceImpl(ServiceRegistrationImpl.java:277)
at org.eclipse.osgi.internal.serviceregistry.ServiceRegistry.lookupServiceRegistrations(ServiceRegistry.java:867)
at org.eclipse.osgi.internal.serviceregistry.ServiceRegistry.getServiceReferences(ServiceRegistry.java:290)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.getAllServiceReferences(BundleContextImpl.java:577)
at org.osgi.util.tracker.ServiceTracker.getInitialReferences(ServiceTracker.java:360)
at org.osgi.util.tracker.ServiceTracker.open(ServiceTracker.java:321)
at com.tibco.xxx.start(xxx.java:150)
at com.tibco.xxx.Activator.start(Activator.java:39)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl$1.run(BundleContextImpl.java:782)
at java.security.AccessController.doPrivileged(Native
Method)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:773)

The exception is thrown while starting a bundle after
the refreshPackages call. I assume the refreshThread is still ongoing in
the background and as part of the process stops and restarts bundles, which
causes OSGi services to be unregistered and then (hopefully) registered
again.

The ServiceTracker of the bundle that is started wants
to look for all services that have a certain property set. However, during
the initial scan of all services, one of them is unregistered, which causes
the seen exception.

There seems to be a race condition in which lookupServiceRegistrations()
acquires the lock to ServiceRegistry and copies the results to an ArrayList.

private List lookupServiceRegistrations(String
clazz, Filter filter) {
List result;
synchronized (this)
{
if (clazz == null)
{ /* all services */
result = allPublishedServices;
} else
{
/* services registered under the class name
*/
result = (List) publishedServicesByClass.get(clazz);
}

if ((result == null)
|| (result.size() == 0)) {
return Collections.EMPTY_LIST;
}

result = new
ArrayList(result); /* make a new list
since we don't want to change the real list */
}

In the meantime the service is unregistered
and removed from allPublishedServices:

void
removeServiceRegistration(BundleContextImpl context, ServiceRegistrationImpl
serviceReg) {
// Remove the ServiceRegistrationImpl
from the list of Services published by BundleContextImpl.
List contextServices = (List) publishedServicesByContext.get(context);
if
(contextServices != null)
{
contextServices.remove(serviceReg);
}

// Remove the ServiceRegistrationImpl
from the list of Services published by Class Name.
String[] clazzes = serviceReg.getClasses();
for
(int
i = 0, size = clazzes.length;
i < size; i++) {
String clazz = clazzes[i];
List services = (List) publishedServicesByClass.get(clazz);
services.remove(serviceReg);
}

// Remove the ServiceRegistrationImpl
from the list of all published Services.
allPublishedServices.remove(serviceReg);
}

However, lookupServiceRegistrations() goes
on to iterate over the result list and runs into the exception above.

for
(Iterator iter = result.iterator(); iter.hasNext();) {
ServiceRegistrationImpl registration = (ServiceRegistrationImpl)
iter.next();
if
(!filter.match(registration.getReferenceImpl())) {
iter.remove();
}
}


Has anyone seen this? Is this a know problem? I guess
I could file a bug for this.

Thanks,

   Tim.

"It is a simple task to make things
complex, but a complex task to make them simple."
 -- Fortune Cookie
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