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

[Jaroslav Bachorik]

On 07/24/2013 01:21 PM, 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.

So, if I understand it correctly, it is not possible to get 100%
accuracy of the thread related counters in situations when you create
and terminate a number of threads rapidly.

In that case this test could be fixed with a small waiting period after
all the joined threads were terminated - just to make sure that all the
exiting threads were properly collected.

The only question remains whether a bug should be filed for the
discrepancy between the thread counters obtained from ThreadMXBean and
the ones coming from different paths.

-JB-

> 
> David
> -----
> 
>> Mandy