Thread.getState() very slow

[Jeremy Manson]

Second, FWIW.  Our users are constantly baffled as to why all of their
blocked-on-epoll threads are listed as RUNNABLE.

Jeremy

On Fri, Aug 13, 2010 at 10:18 AM, Martin Buchholz <martinrb at google.com> wrote:
> As a related project, we could fix the JDK so that threads blocked in IO
> operations would be much more likely to also report a thread state of
> BLOCKED.
>
> Martin
>
> On Fri, Aug 13, 2010 at 09:59, Doug Lea <dl at cs.oswego.edu> wrote:
>>
>> Sorry for the long delay on this...
>>
>> On 07/15/10 23:43, Mandy Chung wrote:
>>>
>>> I think making Thread.threadStatus a volatile field and using
>>> JVMTI_JAVA_LANG_THREAD_STATE_MASK to convert Thread.threadStatus to
>>> Thread.State
>>> enum would be a good solution.
>>>
>>>
>>> It'd be great if Doug can do the experiment and evaluate the performance
>>> impact.
>>> If you want me to prototype the jdk change, let me know and I should be
>>> able to
>>> make some time to do it next week.
>>>
>>
>> I did an equivalent experiment (of just directly accessing
>> threadState via Unsafe.getIntVolatile and comparing it to
>> cached values) and it was about 14X faster.  So anything
>> along these lines would be grat. That said, I decided not
>> to try to rely on getState in the near term. (Among other
>> reasons, it does not usually reflect IO blockage.) So this
>> is off the critical path for now. But someday someone is sure
>> to run into similar performance issues unless implementation
>> is improved.
>>
>> -Doug
>>
>
>