RFR: 8222422: vmTestbase/nsk/jdi/ClassLoaderReference/definedClasses tests failed with Unexpected Exception: null

[Chris Plummer]

On 5/10/19 9:03 PM, Chris Plummer wrote:
> On 5/10/19 8:59 PM, David Holmes wrote:
>> Hi Daniil,
>>
>> On 11/05/2019 12:10 pm, Daniil Titov wrote:
>>> Please review the change that fixes an intermittent failure of the 
>>> test.
>>>
>>> The tests checks the implementation of  the 
>>> com.sun.tools.jdi.ClassLoaderReference class. The problem here is 
>>> that while 
>>> com.sun.tools.jdi.ClassLoaderReferenceImpl.definedClasses() iterates 
>>> over all loaded classes to retrieve a classloader and compares it to 
>>> the current one, some of the classes might become unloaded and 
>>> garbage collected (e.g. 
>>> org.graalvm.compiler.nodes.InliningLog$$Lambda$41.899832640 or 
>>> jdk.internal.reflect.GeneratedConstructorAccessor1, etc.). If this 
>>> happens then the attempt to retrieve a classloader for the collected 
>>> class results in com.sun.jdi.ObjectCollectedException being thrown.
>>
>> That seems odd to me. If you have a reference to the Class then it 
>> can't be unloaded. I would not expect allClasses() to have 
>> weak-references, so a class should not be unloadable while you are 
>> examining it. Unless it is finding VM anonymous classes (which it 
>> should not!).
>>
> I was just typing up something similar. Shouldn't the test do a 
> vm.suspend() and then call disableCollection() on each class returned 
> by vm.allClasses()?
Oh wait, this isn't a test. It's part of JDI. I guess it would be up to 
the user of ClassLoaderReference.definedClasses() to do the suspend. In 
fact I'm not sure there's much purpose in calling 
ClassLoaderReference.definedClasses() without suspending first. Even 
with your changes, the list returned can end up with references to 
unloaded classes.

Chris
>
> Chris
>> David
>> -----
>>
>>> The fix catches this com.sun.jdi.ObjectCollectedException and 
>>> continues iterating over the rest of the classes.
>>>
>>> Webrev: http://cr.openjdk.java.net/~dtitov/8222422/webrev.01
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8222422
>>>
>>> Thanks!
>>> --Daniil
>>>
>>>
>
>