jmx-dev RFR: 8020875 java/lang/management/ThreadMXBean/ResetPeakThreadCount.java fails intermittently

[Jaroslav Bachorik]

On 07/24/2013 02:32 PM, Chris Hegarty wrote:
> On 24/07/2013 12:21, David Holmes wrote:
>> On 24/07/2013 7:31 PM, Mandy Chung wrote:
>>>
>>> On 7/24/2013 4:50 PM, shanliang wrote:
>>>> So we have 2 kinds of issues here:
>>>> 1) the test related, like Thread state checking, we can fix them in
>>>> the test
>>>> 2) MBean.getThreadCount() issue, we can create a bug to trace it (add
>>>> your test case to the bug), and add a workaround (sleep or call 2
>>>> times) in the test to make the test pass. Mandy is the expert and
>>>> better to get her opinion.
>>>
>>> It's probably a race in the VM implementation in determining the thread
>>> count. You will need to diagnose the VM implementation and compare the
>>> thread list and the implementation of getting the thread count (check
>>> hotspot/src/share/vm/services/threadService.cpp)
>>
>> There is a considerable code path between the point where a terminating
>> thread causes Thread.join() to be allowed to return, and the point where
>> the live thread count gets decremented. So using join() does not help
>> here. Arguably JVMTI should have based its counts around the lifecycle
>> of the Java thread not the underlying native thread.
> 
> It appears, from my reading of the code, that this situation ( a thread
> exiting ) should be handled. Or maybe I'm looking at the wrong interface.
> 
> JavaThread::exit(...) {
>   ...
>   ThreadService::current_thread_exiting(this);
>   ...
>   ensure_join(..)
>   ...
> }
> 
> So the exiting thread should be removed from the live thread count
> before Thread.join returns.

Unfortunately, ensure_join(...) is called on line 1860 but
Threads::remove(this), which does the actual cleanup of the live threads
counter, is called only on line 1919, leaving at least a few ns window
when the thread is reported as terminated in java but the counters
haven't been updated yet.

-JB-

> 
> -Chris.
> 
>>
>> David
>> -----
>>
>>> Mandy