RFR: JDK-8210252: com/sun/jdi/DebuggerThreadTest.java fails with NPE
Chris Plummer
chris.plummer at oracle.com
Wed Sep 5 18:56:06 UTC 2018
I was thinking something like the resume() call. At the very least just
try setting finishedThreads = 1 to exercise the error handling.
Chris
On 9/5/18 11:49 AM, Gary Adams wrote:
> I had tried sleeping after each entry in dumpThreads was checked, but the
> failure never occurred.
>
> I had tried using mach5 --jvm-args to set UseZGC, but that never failed.
>
> Could attempt a resume() before calling dumpThreads() - haven't tried
> that , yet.
>
> On 9/5/18, 2:31 PM, Chris Plummer wrote:
>> Ok. Have you found a way to test your changes? Maybe just force or
>> simulate a failure somehow.
>>
>> Chris
>>
>> On 9/5/18 11:26 AM, Gary Adams wrote:
>>> If we go ahead with this proposed fix, the next time it fails
>>> we will have more information about the other threads
>>> captured in the log.
>>>
>>> One last observation, the test that failed was running with UseZGC.
>>> Not sure how that might impact this particular test.
>>>
>>> On 9/5/18, 2:07 PM, Chris Plummer wrote:
>>>>
>>>> Hi Gary,
>>>>
>>>>> If the DebugThreadTarg is resumed prematurely,
>>>>
>>>> The failure explanation seems to hinge on this, but I don't see how
>>>> this can happen. What is resuming DebugThreadTarg? Only the call to
>>>> listenUntilVMDisconnect() should be doing this, and we aren't even
>>>> getting that far. The only thing I can think of is due to some
>>>> other issue (maybe host out of memory so process was killed off),
>>>> the DebugThreadTarg process has exited unexpectedly. In this case I
>>>> guess the fix you have is appropriate defensive programming,
>>>> causing the test to fail when this happens, but still won't explain
>>>> why it happens and also won't prevent future failures of this test.
>>>> Also, this type of Debuggee early exit problem could happen with
>>>> other tests too. I'm leaning towards just closing this bug as CNR.
>>>> I don't think we want to be writing our tests to defend against
>>>> random system related failures, especially when the end result is
>>>> still going to be a test failure that we don't fully understand.
>>>>
>>>> thanks,
>>>>
>>>> Chris
>>>>
>>>> On 9/5/18 7:33 AM, Gary Adams wrote:
>>>>> The DebuggerThreadTest ensures it is in sync
>>>>> at the beginning of RunTests with a breakpoint event
>>>>> in DebuggerThreadTarg ready() method.
>>>>>
>>>>> The DebuggerThreadTest then continues with
>>>>> dumpThreads() and listenUntilVMDisconnect()
>>>>> completes.
>>>>>
>>>>> If the DebugThreadTarg is resumed prematurely,
>>>>> the main thread in the debuggee could complete
>>>>> before the dumpThreads enumeration is complete.
>>>>>
>>>>> DebuggerThreadTest
>>>>> main()
>>>>> startTests()
>>>>> runTests()
>>>>> startTo( "DebuggerThreadTarg.ready()")
>>>>> dumpThreads()
>>>>> listenUntilVMDisconnect()
>>>>>
>>>>> DebuggerThreadTarg
>>>>> main()
>>>>> ready()
>>>>>
>>>>> Revised fix:
>>>>> - Prevents the NPE from a finished thread group
>>>>> - Fails the test with a message indicating
>>>>> number of premature completed threads.
>>>>>
>>>>> 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
>>>>> @@ -1,5 +1,5 @@
>>>>> /*
>>>>> - * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All
>>>>> rights reserved.
>>>>> + * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All
>>>>> rights reserved.
>>>>> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
>>>>> *
>>>>> * This code is free software; you can redistribute it and/or
>>>>> modify it
>>>>> @@ -76,8 +76,16 @@
>>>>> Thread list[] = new Thread[listThreads * 2];
>>>>> int gotThreads = tg.enumerate(list, true);
>>>>> for (int i = 0; i < Math.min(gotThreads, list.length); i++){
>>>>> + int finishedThreads = 0;
>>>>> Thread t = list[i];
>>>>> - String groupName = t.getThreadGroup().getName();
>>>>> + ThreadGroup tga = t.getThreadGroup();
>>>>> + String groupName;
>>>>> + if (tga == null) {
>>>>> + groupName = "<completed>";
>>>>> + finishedThreads++ ;
>>>>> + } else {
>>>>> + groupName =tga.getName();
>>>>> + }
>>>>>
>>>>> System.out.println("Thread [" + i + "] group = '" +
>>>>> groupName +
>>>>> @@ -89,7 +97,10 @@
>>>>> failure("FAIL: non-daemon thread '" + t.getName() +
>>>>> "' found in ThreadGroup '" + groupName +
>>>>> "'");
>>>>> }
>>>>> -
>>>>> + if (finishedThreads > 0 ) {
>>>>> + failure("FAIL: " + finishedThreads +
>>>>> + " threads completed while VM suspended.");
>>>>> + }
>>>>> }
>>>>> }
>>>>>
>>>>>
>>>>> On 9/4/18, 3:15 PM, Chris Plummer wrote:
>>>>>> 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 +
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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