RFR: JDK-8210252: com/sun/jdi/DebuggerThreadTest.java fails with NPE

[Chris Plummer]

Hi Gary,

The failed case only had:

Thread [0] group = 'system' name = 'Reference Handler' daemon = true
Thread [1] group = 'system' name = 'Finalizer' daemon = true
Thread [2] group = 'system' name = 'Signal Dispatcher' daemon = true
Thread [3] group = 'system' name = 'process reaper' daemon = true

That would indicate that 'main' is likely the thread that exited. Seems 
odd. Isn't that the thread that the test is executing in?

If you can't reproduce it, maybe it would be better to commit a 
diagnostic fix like the one I suggested and keep an eye on it. However, 
it only seems to have failed once due to this reason, so unless it is a 
new problem we may never see it again.

Chris

On 9/4/18 11:28 AM, Gary Adams wrote:
> I haven't been able to reproduce the problem locally.
> Trying larger test runs on mach5 now.
>
> Here's the output from a successful test run.
> If any of the threads exited, they would have a null group name.
>
> Howdy!
> Thread [0] group = 'system' name = 'Reference Handler' daemon = true
> Thread [1] group = 'system' name = 'Finalizer' daemon = true
> Thread [2] group = 'system' name = 'Signal Dispatcher' daemon = true
> Thread [3] group = 'system' name = 'process reaper' daemon = true
> Thread [4] group = 'main' name = 'main' daemon = false
> Thread [5] group = 'main' name = 'pool-1-thread-1' daemon = true
> Thread [6] group = 'AgentVMThreadGroup' name = 'AgentVMThread' daemon 
> = false
> Thread [7] group = 'AgentVMThreadGroup' name = 'output reader' daemon 
> = false
> Thread [8] group = 'AgentVMThreadGroup' name = 'output reader' daemon 
> = false
> Thread [9] group = 'AgentVMThreadGroup' name = 'Thread-5' daemon = true
> Thread [10] group = 'InnocuousThreadGroup' name = 'Common-Cleaner' 
> daemon = true
> Thread [11] group = 'JDI [1485331767]' name = 'JDI Internal Event 
> Handler' daemon = true
> Thread [12] group = 'JDI [1485331767]' name = 'JDI Target VM 
> Interface' daemon = true
> Goodbye from DebuggerThreadTarg!
>
>
> On 9/4/18, 2:16 PM, Chris Plummer wrote:
>> Can you reproduce the problem? If so, maybe to find out which thread 
>> is a problem you could check for null, print the thread info, and 
>> then fail the test.
>>
>> Chris
>>
>> On 9/4/18 11:14 AM, Gary Adams wrote:
>>> I'm not sure which thread exited causes the NPE.
>>> This patch will let  the test continue and at least
>>> let the list of threads be processed.
>>>
>>> The test walks up the parents to the initial thread
>>> and then "enumerates()" the set of the threads to check.
>>> There is an inherent race condition in enumerate()
>>> that recognizes it is a snapshot of a moving target.
>>>
>>> On 9/4/18, 1:51 PM, Chris Plummer wrote:
>>>> Hi Gary,
>>>>
>>>> Why has the thread exited if the debuggee is still running?
>>>>
>>>> Chris
>>>>
>>>> On 9/4/18 5:22 AM, Gary Adams wrote:
>>>>> Here's a quick fix to avoid the NPE using a getThreadGroup() which 
>>>>> could be null
>>>>> if the thread has terminated.
>>>>>
>>>>>   Issue: https://bugs.openjdk.java.net/browse/JDK-8210252
>>>>>
>>>>> diff --git a/test/jdk/com/sun/jdi/DebuggerThreadTest.java 
>>>>> b/test/jdk/com/sun/jdi/DebuggerThreadTest.java
>>>>> --- a/test/jdk/com/sun/jdi/DebuggerThreadTest.java
>>>>> +++ b/test/jdk/com/sun/jdi/DebuggerThreadTest.java
>>>>> @@ -77,7 +77,8 @@
>>>>>          int gotThreads = tg.enumerate(list, true);
>>>>>          for (int i = 0; i < Math.min(gotThreads, list.length); i++){
>>>>>              Thread t = list[i];
>>>>> - String groupName = t.getThreadGroup().getName();
>>>>> + ThreadGroup tga = t.getThreadGroup();
>>>>> + String groupName = (tga == null ? "<completed>": tga.getName());
>>>>>
>>>>>              System.out.println("Thread [" + i + "] group = '" +
>>>>>                                 groupName + 
>>>>
>>>>
>>>
>>
>>
>