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From Vlad Rozov <v.ro...@datatorrent.com>
Subject Re: Occasional Out of order tuples when emitting from a thread
Date Tue, 21 Feb 2017 20:31:02 GMT
Please see Threads section at 
http://apex.apache.org/docs/apex/development_best_practices/

Note that an operator has only one thread created by the Apex that it 
can use to interact with the system. Starting with 3.5.0 release, this 
is enforced by the platform and it will throw an exception if an 
operator tries to emit on a different thread.

Thank you,

Vlad

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On 2/21/17 11:54, Munagala Ramanath wrote:
> To amplify Sandesh's answer a bit, the main operator thread invokes 
> user callbacks like beginWindow(), endWindow(), process() method of 
> input ports, and emitTuples() in input operators.
>
> Additionally, if the operator implements the IdleTimeHandler, and if 
> the operator is deemed to be idle, the handleIdleTime() callback will 
> be called. All tuple output must be done in one of these callbacks.
>
> So you can check the thread-safe queue in any of these callbacks and 
> emit output tuples as needed.
>
> Ram
>
> On Tue, Feb 21, 2017 at 11:42 AM, Sandesh Hegde 
> <sandesh@datatorrent.com <mailto:sandesh@datatorrent.com>> wrote:
>
>     -Removed dev@
>
>     Operators can implement idle Time Handler.
>     https://www.datatorrent.com/docs/apidocs/com/datatorrent/api/Operator.IdleTimeHandler.html
>     <https://www.datatorrent.com/docs/apidocs/com/datatorrent/api/Operator.IdleTimeHandler.html>
>
>     On Tue, Feb 21, 2017 at 11:33 AM Sunil Parmar
>     <sparmar@threatmetrix.com <mailto:sparmar@threatmetrix.com>> wrote:
>
>         Ram,
>         Thanks for the prompt response. If we use the approach you
>         suggested we’re dependent on main thread’s process call I.e.
>         Tuples in the thread safe queue gets only processed when main
>         thread is processing incoming tuples. How can we explicitly
>         call the process from polling of delay queue ?
>
>         Just for reference here’s the sample code snippet for our
>         operator.
>
>         public class MyOperator extends BaseOperator implements
>
>                 Operator.ActivationListener<Context.OperatorContext> {
>
>         …..
>
>         @InputPortFieldAnnotation
>
>         public transient DefaultInputPort<String> kafkaStreamInput =
>
>         new DefaultInputPort<String>() {
>
>                 List<String> errors = new ArrayList<String>();
>
>         @Override
>
>         public void process(String consumerRecord) {
>
>         //Code for normal tuple process
>
>         //Code to poll thread safe queue
>
>         }
>
>
>         *————————————**—————————————————————————*
>         *From: *Munagala Ramanath <ram@datatorrent.com
>         <mailto:ram@datatorrent.com>>
>         *To: *users@apex.apache.org <mailto:users@apex.apache.org>
>         *CC: *"dev@apex.apache.org <mailto:dev@apex.apache.org>"
>         <dev@apex.apache.org <mailto:dev@apex.apache.org>>, Allan De
>         Leon <adeleon@threatmetrix.com
>         <mailto:adeleon@threatmetrix.com>>, Tim Zhu
>         <tzhu@threatmetrix.com <mailto:tzhu@threatmetrix.com>>
>         *Subject: *Re: Occasional Out of order tuples when emitting
>         from a thread
>         *Date: *2017-02-21 10:08 (-0800)
>         *List: *users@apex.apache.org
>         <https://lists.apache.org/list.html?users@apex.apache.org>
>
>         Please note that tuples should not be emitted by any thread other than the
>         main operator thread.
>
>         A common pattern is to use a thread-safe queue and have worker threads
>         enqueue
>         tuples there; the main operator thread then pulls tuples from the queue and
>         emits them.
>
>         Ram
>
>         _______________________________________________________
>
>         Munagala V. Ramanath
>
>         Software Engineer
>
>         E:ram@datatorrent.com <mailto:ram@datatorrent.com>  | M:(408) 331-5034
<tel:%28408%29%20331-5034>  | Twitter: @UnknownRam
>
>         www.datatorrent.com <http://www.datatorrent.com>   |apex.apache.org <http://apex.apache.org>
 
>
>         From: Sunil Parmar <sparmar@threatmetrix.com
>         <mailto:sparmar@threatmetrix.com>> Date: Tuesday, February 21,
>         2017 at 10:05 AM To: "users@apex.apache.org
>         <mailto:users@apex.apache.org>" <users@apex.apache.org
>         <mailto:users@apex.apache.org>>, "dev@apex.apache.org
>         <mailto:dev@apex.apache.org>" <dev@apex.apache.org
>         <mailto:dev@apex.apache.org>> Cc: Allan De Leon
>         <adeleon@threatmetrix.com <mailto:adeleon@threatmetrix.com>>,
>         Tim Zhu <tzhu@threatmetrix.com <mailto:tzhu@threatmetrix.com>>
>         Subject: Occasional Out of order tuples when emitting from a
>         thread
>         Hi there,
>         We have the following setup:
>
>           * we have a generic operator that’s processing tuples in its
>             input port
>           * in the input port’s process method, we check for a
>             condition, and:
>               o if the condition is met, the tuple is emitted to the
>                 next operator right away (in the process method)
>               o Otherwise, if the condition is not met, we store the
>                 tuple  in some cache and we use some threads that
>                 periodically check the condition to become true. Once
>                 the condition is true, the threads call the emit
>                 method on the stored tuples.
>
>         With this setup, we occasionally encounter the following error:
>         2017-02-15 17:29:09,364 ERROR
>         com.datatorrent.stram.engine.GenericNode: Catastrophic Error:
>         Out of sequence BEGIN_WINDOW tuple 58a4046100003b7f on port
>         transformedJSON while expecting 58a4046100003b7e
>         Is there a way to make the above work correctly?
>         If not, can you recommend a better way of doing this?
>         How can we ensure window assignment is done synchronously
>         before emitting tuples ?
>         Thanks very much in advance…
>         -allan
>
>     -- 
>     /Join us at ApexBigDataWorld-San Jose
>     <http://www.apexbigdata.com/san-jose.html>, April 4, 2017!/
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>
> -- 
>
> _______________________________________________________
>
> Munagala V. Ramanath
>
> Software Engineer
>
> E: ram@datatorrent.com <mailto:ram@datatorrent.com> | M: (408) 
> 331-5034 | Twitter: @UnknownRam
>
> www.datatorrent.com <http://www.datatorrent.com>  | apex.apache.org 
> <http://apex.apache.org>
>

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