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

[Gary Adams]

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 + 
>>>
>>>
>>
>
>