9:48 a.m.
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(a)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/co...
>
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