[infinispan-dev] Distributed Executor remote cancellation

[Dennis Reed]

On 03/30/2016 12:26 PM, Sanne Grinovero wrote:
> On 30 March 2016 at 17:40, William Burns <mudokonman at gmail.com> wrote:
>> You can still attempt to cancel a task.  This email is specifically about
>> interruption though.  Let me explain the nuances in a bit more detail.
>>
>> With the suggestion we would still fully support if the task hasn't yet
>> started that it would be cancellable.
>>
>> However when you cancel a task, there is an mayInterruptIfRunning boolean.
>> If mayInterruptIfRunning is true and the task is already running it will try
>> to interrupt the thread processing it.  This is what this email trail is
>> about.  We all know that java interruption can be flaky to begin with and
>> then adding a remote aspect to it, it becomes even more unreliable.
>>
>> So do you guys think we need to support "interrupting" a task in progress?
>
> Yes, absolutely! Resources are precious :)
>
> See also the reasoning of our old friend:
>   - https://corner.squareup.com/2016/01/query-sniper.html
>
> Take the example of a non-correctly tuned Hibernate Search "rebuild
> all indexes" task. On a non-trivial data set it might need to run for
> weeks... you need a way to kill it.

Do you want a way to "kill" it, or a way to "interrupt" it?  Your reply 
appeared to equate these, but the terms are actually quite different.

Interruption is more of a "hey, if you don't mind could you please 
stop?", and requires the code to correctly handle it.  The vast majority 
of code isn't written with interruption in mind.

As William mentioned, interruption is not reliable (and there isn't any 
reliable and safe way to stop a single thread in Java).  So the question 
is whether we want to support "ask it to stop, and it might stop or it 
might not" functionality.

-Dennis


> Thanks,
> Sanne
>
>>
>>   - Will
>>
>> On Wed, Mar 30, 2016 at 12:29 PM Tristan Tarrant <ttarrant at redhat.com>
>> wrote:
>>>
>>> I agree with Sanne, we need cancellable  tasks.
>>>
>>> Tristan
>>>
>>> On 30/03/2016 18:19, Sanne Grinovero wrote:
>>>> The term "Interruption" might have been too specific, but being able
>>>> to cancel a task seems essential to me.
>>>>
>>>> On 30 March 2016 at 17:04, William Burns <mudokonman at gmail.com> wrote:
>>>>> Recently we have been moving a lot of our methods that return Future
>>>>> [1] to
>>>>> CompletableFuture [2].  Unfortunately the latter, CompletableFuture,
>>>>> doesn't
>>>>> allow for cancellation of the future, since there is no thread tied to
>>>>> it.
>>>>> So I am proposing that our DistributedExecutorService [3] no longer
>>>>> allows
>>>>> for interruption of remote threads on a cancellation.  This way we can
>>>>> have
>>>>> our distributed executor service return CompletableFuture instances
>>>>> which do
>>>>> not support interruption.
>>>>>
>>>>> Also to note that DistributedExecutorService extends ExecutorService
>>>>> which
>>>>> returns a normal Future which is documented as allowing cancellation.
>>>>> In
>>>>> this case I would just document on DistributedExecutorService that we
>>>>> don't
>>>>> support interruption anyways.
>>>>>
>>>>> Does anyone require the use of interruptable tasks with Distributed
>>>>> Executor?
>>>>>
>>>>> Thanks,
>>>>>
>>>>>    - Will
>>>>>
>>>>> [1]
>>>>>
>>>>> https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Future.html
>>>>> [2]
>>>>>
>>>>> https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html
>>>>> [3]
>>>>>
>>>>> https://docs.jboss.org/infinispan/8.1/apidocs/org/infinispan/distexec/DistributedExecutorService.html
>>>>>
>>>>> _______________________________________________
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>>>
>>> --
>>> Tristan Tarrant
>>> Infinispan Lead
>>> JBoss, a division of Red Hat
>>> _______________________________________________
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>>> infinispan-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>
>>
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