Review request: 8010151 : nsk/regression/b6653214 fails "assert(snapshot != NULL) failed: Worker should not be started"

[Zhengyu Gu]

Thanks for the suggestion, it is a better solution, the race can result 
snapshot not been freed.

-Zhengyu

On 4/3/2013 7:59 PM, Dean Long wrote:
> If the analysis by Christian Törnqvist is correct then you should be 
> able to reproduce the problem by adding sleeps
> where he suggested.  You will then probably discover that "volatile" 
> does not solve the problem.  I think there are
> still races and the code is not MT-safe.
>
> This may not solve all the races, but you could try something like:
>
> bool MemTracker::start_worker(MemSnapshot *snapshot) {
>   assert(_worker_thread == NULL, "Just Check");
>   _worker_thread = new (std::nothrow) MemTrackWorker(snapshot);
>
> so that the worker thread doesn't need to call get_snapshot().
>
> dl
>
> On 4/3/2013 3:21 PM, Zhengyu Gu wrote:
>> Thanks for pointing it out. Yes, it should be a volatile pointer.
>>
>> -Zhengyu
>>
>> On 4/3/2013 2:40 PM, Coleen Phillimore wrote:
>>>
>>> Is the _snapshot volatile or what it points to is volatile? The code 
>>> you have is what it points to.
>>>
>>> I think you want:
>>>
>>> *!    static_   _MemSnapshot*   volatile  _snapshot;*
>>>
>>> Coleen
>>>
>>> On 04/03/2013 01:59 PM, Zhengyu Gu wrote:
>>>> The assertion appears due to snapshot variable still is not visible 
>>>> to worker thread, so make snapshot volatile.
>>>>
>>>> NMT creates snapshot before starting NMT worker thread and the 
>>>> snapshot is released by worker thread during shutdown, so the 
>>>> assertion should not fail. I can not reproduce the problem 
>>>> with/without volatile modifier.
>>>>
>>>>
>>>> Bug: http://bugs.sun.com/view_bug.do?bug_id=8010151
>>>> Webrev: http://cr.openjdk.java.net/~zgu/8010151/webrev.00/ 
>>>> <http://cr.openjdk.java.net/%7Ezgu/8010151/webrev.00/>
>>>>
>>>> Test:
>>>>   nsk/regression/b6653214  on Windows x64
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> -Zhengyu
>>>>
>>>
>>
>

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