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

[Gary Adams]

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 + 
>
>