RFR: 8253429: Error reporting should report correct state of terminated/aborted threads

[David Holmes]

Hi Thomas,

On 25/09/2020 2:31 pm, Thomas Stuefe wrote:
> On Thu, 24 Sep 2020 18:14:10 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:
> 
>> For some non-JavaThread, their object instances can outlast threads' lifespan. For example, we still can query/report
>> thread's state after thread terminated.
>> But the query/report currently returns wrong state. E.g. a terminated thread appears to be alive and seemly has valid
>> thread stack, etc.
>> This patch sets non-JavaThread's state to ZOMBIE just before it terminates, so that we can distinguish terminated
>> thread from live thread.
>> Also, thread should not report its SMR info, if it has terminated or it never started (thread->osthread() == NULL).
>>
>> Note: Java thread does not have such issue, its thread object is deleted before thread terminates.
> 
> Hi Zhengyu,
> 
> Could this expose us to a race?
> 
> What I mean is: on Linux and BSD I see this code in os::create_thread() after thread creation and after the initial
> handshake with the parent thread:
> 
>> A pthread_create ...
>> B initial handshake...
>>
>> C // Aborted due to thread limit being reached
>>   if (state == ZOMBIE) {
>>     thread->set_osthread(NULL);
>>     delete osthread;
>>     return false;
>>   }
> 
> (Weirdly enough we don't do (C) for Windows and AIX).
> 
> I may be wrong do not find anywhere in the code where we set the ZOMBIE state today. So (C) may be just dead code now.

Funnily enough it seems to be dead code that you created:

https://bugs.openjdk.java.net/browse/JDK-8078513

but mea culpa too as I missed it in the review. :)

Otherwise, yes this would be a theoretical race. So lets just delete the 
above.

Cheers,
David

> With your patch, we now set the state to ZOMBIE in post_run. If child finishes and sets ZOMBIE state before parent
> reaches (C) os::create_thread would return not false even though the child thread started correctly and ran through?
> 
> -------------
> 
> PR: https://git.openjdk.java.net/jdk/pull/341
>