[Hawkular-dev] [metrics] Looking for advice on ListenableFuture usage

[Thomas Segismont]

Sorry I overlooked the metrics-core code.

Indeed, almost every call where a ListenableFuture returned by the C* 
driver is involved uses the overloaded version (with the metricsTasks 
ListenableExecutor instance).
Should I open a JIRA for the few places where it's missing?

My understanding from you reply is that:
* all transformations on ListenableFuture returned by the C* driver 
should happen in a thread of the metricsTasks pool
==> use the overloaded version
* subsequent transformations may happen on the metricsTasks thread or on 
the thread executing the rest handler code
==> use the base version
Is that correct?

Thanks

Le 16/01/2015 14:23, John Sanda a écrit :
> In the metrics code, at least where a response from the C* driver is involved, the versions that take an executor is used almost everywhere. We do not want to block I/O threads doing work so in general it is best to use the overloaded versions of the methods.
B>
>> On Jan 16, 2015, at 4:47 AM, Thomas Segismont <tsegismo at redhat.com> wrote:
>>
>> Hi everyone,
>>
>> I'm looking for advice on how to use Futures#transform[1] and friends
>> (#addCallback, #withFallback)
>>
>> These methods all have an overloaded version which takes a JDK Executor
>> instance as additional argument.
>>
>> When the base method is called, Guava will use the so-called
>> "sameThreadExecutor". Consequently, the code will be executed:
>> * by the caller thread, if the underlying Future has completed already
>> * otherwise, by the thread completing the underlying Future
>>
>> When the overloaded method is called, Guava will submit tasks to the
>> provided executor.
>>
>> In the metrics code right now, the base method is used almost
>> everywhere. Considering that in most cases it will take more time to get
>> the response from C* than to complete the REST Handler code, it's the
>> Datastax driver threads which will execute the chain of callbacks, down
>> to the call to javax.ws.rs.container.AsyncResponse#resume
>>
>> Could that be a problem? I guess it's safe when callbacks only
>> transforms the data loaded. I'm not sure about the call to
>> AsyncResponse#resume.
>>
>> Thoughts?
>>
>> Thanks,
>> Thomas
>>
>>
>> [1]
>> http://docs.guava-libraries.googlecode.com/git-history/v16.0.1/javadoc/com/google/common/util/concurrent/Futures.html
>>
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