RFR: 6815126 intermittent SimulResumerTest.java failure

[shanliang]

Jaroslav Bachorik wrote:
> Thanks Shanliang, it is clear now.
>
> The patch will get rid off the IOOBE but I have my doubts about what 
> the test actually tests. It is supposed to make sure that certain 
> operations will not throw NPE when the debugged thread is resumed 
> (from a concurrent debugger thread) before the operation has managed 
> to finish. However, there seems to be no synchronization logic between 
> the thread invoking the operations and the thread resuming the paused 
> debugged thread, relying only on hitting this condition by chance.
>
> This test seems to be a good candidate for a thorough revision/rewrite.
Not sure how to make the checking happen during a "resuming" window, the 
test creates 2 threads and each repeats "resume"10000 times, and one 
another thread repeats checking with 100ms sleeping time,  just hoping 
some checking would fail into a resuming window.

Shanliang
>
> -JB-
>
> On 31.3.2014 11:26, shanliang wrote:
>> Erik Gahlin wrote:
>>> I also like to understand better.
>> Possibly my previous reply was not clear enough or I missed something
>> there.
>>
>> The test was to test JDK-6751643 as I cited in the last mail, here is
>> the info from JDK-6751643 to which this test was developed:
>> ------
>> This bug can only occur if a debugger has multiple threads and calls any
>> of the following methods in one thread while simultaneously resuming the
>> same debuggee thread in a different debugger thread. Debuggers shouldn't
>> do this because it is a race condition and the result returned by these
>> methods will vary depending upon just where in the processing of these
>> methods the resume takes effect. EG, the frameCount() method could
>> return 6 in a case where the debuggee has already been resumed and there
>> are no frames.
>> ------
>>
>> To reproduce the bug, test did mainly 2 things by different threads:
>> 1) received vm events and resumed vm, this was done by thread "Thread-1"
>> in the class TestScaffold which registered a listener and called the
>> following method:
>>     /**
>>      * Events handled directly by scaffold always resume (well, almost
>> always)
>>      */
>>         public void eventSetComplete(EventSet set) {
>>         // The listener in connect(..) resumes after receiving our
>>         // special VMDeathEvent.  We can't also do the resume
>>         // here or we will probably get a VMDisconnectedException
>>         if (!containsOurVMDeathRequest(set)) {
>>             traceln("TS: set.resume() called");
>>             set.resume();
>>         }
>>   }
>>
>> 2) called the method "check" in the class SimulResumerTarg, to see
>> whether a NullPointerException was thrown, the thread name was "test
>> resumer" (better to named as "checking thread"?)
>>
>> So one thread was doing resume, another thread was doing check at same.
>> I added the code to see the different values of  frames.size() at 
>> line 185:
>>     for (i=0; i<10:i++) {
>>         System.out.println("---frames.size(): "+frames.size());
>>         Thhread.sleep(200);
>>     }
>>
>> if printing out frames, sometime we could see one more frame:
>>     ------------------ java.lang.Thread.yield()+-1 in thread instance of
>> SimulResumerTarg(name='Thread 2', id=109)
>>
>>
>> Shanliang
>>>
>>> I looked at this failure before and I couldn't see what was wrong, not
>>> in the test or product.
>>>
>>> Erik
>>>
>>> Jaroslav Bachorik skrev 3/27/14 4:49 PM:
>>>> On 27.3.2014 15:49, shanliang wrote:
>>>>> Hi,
>>>>>
>>>>> The call
>>>>>     thr.frames(0, frames.size() - 1);
>>>>> suffers a synchronization issue, the size may be changed after
>>>>> frames.size() returns.
>>>>
>>>> Any idea why there is a synchronization issue? The code seems to be
>>>> intended to run only when a breakpoint is hit and the target thread
>>>> is suspended.
>>>>
>>>> -JB-
>>>>
>>>>>
>>>>> webrev:
>>>>> http://cr.openjdk.java.net/~sjiang/JDK-6815126/00/
>>>>>
>>>>> bug:
>>>>> https://bugs.openjdk.java.net/browse/JDK-6815126
>>>>>
>>>>> Shanliang
>>>>
>>>
>>
>