Q: 8071326: ThreadPoolExecutor in endless thread creation loop if workQueue.take() throws RuntimeException

[David Holmes]

On 28/01/2015 7:03 AM, Lev Priima wrote:
> Yes. And if we have BlockingQueue w/ some amount of tasks which fail
> with exceptions, same amount of threads(not limited by neither
> maximumPoolSize/corePoolSize) will hang under TPE which takes tasks from
> this queue.
>
> It may cause problems if queue has a big percentage of exception-fail
> tasks and we eventually get OOME while unable to create new native thread.

If you use your pathological example then of course you can get into a 
situation where the thread creation outpaces the thread termination - it 
takes time and CPU cycles for a thread to actually complete.

A BlockingQueue implementation should not have an expected failure mode 
that results in regularly throwing Errors or RuntimeExceptions. Such a 
BQ implementation would need to be fixed in my opinion.

The TPE is working as designed - if errors/runtime-exceptions are 
encountered the worker thread will terminate and be replaced by a fresh 
worker. If you keep feeding the worker threads such exceptions then you 
incur a high rate of thread churn. So don't do that. :)

Cheers,
David

> Lev
>
> On 01/27/2015 11:31 PM, Martin Buchholz wrote:
>>
>>
>> On Tue, Jan 27, 2015 at 7:43 AM, Lev Priima <lev.priima at oracle.com
>> <mailto:lev.priima at oracle.com>> wrote:
>>
>>     And these thread will be cleaned only when whole TPE finished.
>>
>>
>> Is this really true?  Each thread should be replaced while running and
>> so the total number of threads retained by the TPE at any one time
>> should be no more than core pool size.
>