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https://issues.apache.org/jira/browse/FLINK-3674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15585557#comment-15585557
 ] 

ASF GitHub Bot commented on FLINK-3674:
---------------------------------------

Github user StefanRRichter commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2570#discussion_r83861268
  
    --- Diff: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/AbstractStreamOperator.java
 ---
    @@ -390,4 +425,141 @@ public void close() {
                        output.close();
                }
        }
    +
    +   // 
------------------------------------------------------------------------
    +   //  Watermark handling
    +   // 
------------------------------------------------------------------------
    +
    +   /**
    +    * Returns a {@link InternalTimerService} that can be used to query 
current processing time
    +    * and event time and to set timers. An operator can have several timer 
services, where
    +    * each has its own namespace serializer. Timer services are 
differentiated by the string
    +    * key that is given when requesting them, if you call this method with 
the same key
    +    * multiple times you will get the same timer service instance in 
subsequent requests.
    +    *
    +    * <p>Timers are always scoped to a key, the currently active key of a 
keyed stream operation.
    +    * When a timer fires, this key will also be set as the currently 
active key.
    +    *
    +    * <p>Each timer has attached metadata, the namespace. Different timer 
services
    +    * can have a different namespace type. If you don't need namespace 
differentiation you
    +    * can use {@link VoidNamespaceSerializer} as the namespace serializer.
    +    *
    +    * @param name The name of the requested timer service. If no service 
exists under the given
    +    *             name a new one will be created and returned.
    +    * @param keySerializer {@code TypeSerializer} for the keys of the 
timers.
    +    * @param namespaceSerializer {@code TypeSerializer} for the timer 
namespace.
    +    * @param triggerable The {@link Triggerable} that should be invoked 
when timers fire
    +    *
    +    * @param <K> The type of the timer keys.
    +    * @param <N> The type of the timer namespace.
    +    */
    +   public <K, N> InternalTimerService<N> getInternalTimerService(
    +                   String name,
    +                   TypeSerializer<K> keySerializer,
    +                   TypeSerializer<N> namespaceSerializer,
    +                   Triggerable<K, N> triggerable) {
    +
    +           @SuppressWarnings("unchecked")
    +           HeapInternalTimerService<K, N> service = 
(HeapInternalTimerService<K, N>) timerServices.get(name);
    +
    +           if (service == null) {
    +                   if (restoredServices != null && 
restoredServices.containsKey(name)) {
    +                           @SuppressWarnings("unchecked")
    +                           HeapInternalTimerService.RestoredTimers<K, N> 
restoredService =
    --- End diff --
    
    `contains()` + `remove()` seems a bit redundant for this use. I would just 
always remove and check the return value for null. 


> Add an interface for Time aware User Functions
> ----------------------------------------------
>
>                 Key: FLINK-3674
>                 URL: https://issues.apache.org/jira/browse/FLINK-3674
>             Project: Flink
>          Issue Type: New Feature
>          Components: Streaming
>    Affects Versions: 1.0.0
>            Reporter: Stephan Ewen
>            Assignee: Aljoscha Krettek
>
> I suggest to add an interface that UDFs can implement, which will let them be 
> notified upon watermark updates.
> Example usage:
> {code}
> public interface EventTimeFunction {
>     void onWatermark(Watermark watermark);
> }
> public class MyMapper implements MapFunction<String, String>, 
> EventTimeFunction {
>     private long currentEventTime = Long.MIN_VALUE;
>     public String map(String value) {
>         return value + " @ " + currentEventTime;
>     }
>     public void onWatermark(Watermark watermark) {
>         currentEventTime = watermark.getTimestamp();
>     }
> }
> {code}



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