Hi Mandy,

On 08/08/2017 18:03, mandy chung wrote:
Throwing UOE would be clearer than throwing UndeclaredThrowableException and ReflectionException.

That's what will happen if someone had a custom implementation
of ThreadMXBean which is compiled against JDK 9 but runs in JDK 10,
and therefore does not have the new methods. Then it inherits
the default body that throes UOE.

With the default body then the implementation can still be compiled
against jdk 10, without having to add the new method.

However MBean proxy simply forwards the call to the remote MBeanServer and calls invoke or getAttribute/setAttribute. NoSuchMethodException will be thrown in the remote VM and the client would get UndeclaredThrowableException or ReflectionException.

You will get UndeclaredThrowableException if the remote VM is a JDK 9
VM and the client is JDK 10 VM and that's OK.

I don't see how the client will invoke the default method unless the JMX MBeanInvocationHandler catches the exception and have special handling to the default methods.

That's not what we're trying to address here.

For the case of missing method in the remote VM but the client has the default method, I got UndeclaredThrowableException. Is that what you see?

That's what I would expect. I did some testing to verify that if an
interface I had a default method m and an MBean M implemented I,
providing an implementation of m, then the result you get by calling
JMX.newMXBeanProxy(connection, name, I.class).m() is actually what
is returned by M.m(), not what is returned by I.m().

This means that you can evolve MBean interfaces by adding methods
to them as long as you provide a default body (which is rather cool :-))

best regards,

-- daniel


On 8/8/17 2:22 AM, Daniel Fuchs wrote:
Hi Ujwal,

I have made a small experiments and it seems that having
a default body doesn't prevent an interface method from
being called from either a JMX or a Platform proxy.

So in the light of this I'll suggest to add a default body
that throw UnsupportedOperationException to the new methods
added to the ThreadMXBean interface, and add an @implSpec
to specify that if not implemented, the method will throw
an UnsupportedOperationException.

This should guarantee better backward compatibility in case
someone has implemented the ThreadMXBean interface.

Mandy, would you agree?

best regards

-- daniel

On 08/08/2017 09:27, Ujwal Vangapally wrote:

below is the link to new webrev incorporating review comments.

webrev: http://cr.openjdk.java.net/~uvangapally/webrev/2017/8185003/webrev.02/

verified that

MBeanServerConnection.invoke throws ReflectionException when invoked with a method that doesn't exist in remote MBean server.

UndeclaredThrowableException will be throwed when a client gets proxy of remote MBean server and calls a method that doesn't exist on remote Mbean server.

do we need to develop Automated tests for verifying above cases ?


On 8/4/2017 5:42 AM, Mandy Chung wrote:
On Aug 3, 2017, at 2:10 PM, Daniel Fuchs <daniel.fu...@oracle.com> wrote:

Hi Mandy,

On 03/08/17 21:04, Mandy Chung wrote:
Adding a public method to an interface is an incompatible source change unless there is a default body. On the other hand I am not sure how MXBean proxies will work when proxying an interface containing a default body. It would be interesting to check this.

ThreadMXBean is a platform MXBean and so JDK implementation is the one implementing it. The real question here is that when MBeanServerConnection.invoke is called on this new method that does not exist in the remote MBeanServer (running on JDK 9 for example), does it get javax.management.ReflectionException? Or something else?
I believe that will be a ReflectionException:

Similarly, when the client gets a proxy of ThreadMXBean from a remote MBeanServer running on JDK 9 VM, and it calls this method, what exception does it get? We may need to update the spec to indicate this error cases if it’s not clear. The notes in ManagementFactory.newPlatformMXBeanProxy covers some cases due to the difference in the client/server are running on.
AFAIK that should be handled by the proxy code - I'd expect that you
will get an UndeclaredThrowableException wrapping the ReflectionException. http://hg.openjdk.java.net/jdk9/dev/jdk/file/65464a307408/src/java.management/share/classes/javax/management/MBeanServerInvocationHandler.java#l308
Thanks. That’s what I think but need assurance. We should add tests to verify.


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