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Date: Fri, 21 Oct 2016 13:16:58 +0000 (UTC)
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Subject: [jira] [Commented] (FLINK-4862) NPE on EventTimeSessionWindows with
 ContinuousEventTimeTrigger
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archived-at: Fri, 21 Oct 2016 13:17:00 -0000


    [ https://issues.apache.org/jira/browse/FLINK-4862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15595033#comment-15595033 ] 

ASF GitHub Bot commented on FLINK-4862:
---------------------------------------

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

    https://github.com/apache/flink/pull/2671#discussion_r84464167
  
    --- Diff: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/windowing/triggers/ContinuousEventTimeTrigger.java ---
    @@ -88,9 +96,13 @@ public TriggerResult onProcessingTime(long time, W window, TriggerContext ctx) t
     	@Override
     	public void clear(W window, TriggerContext ctx) throws Exception {
     		ReducingState<Long> fireTimestamp = ctx.getPartitionedState(stateDesc);
    -		long timestamp = fireTimestamp.get();
    -		ctx.deleteEventTimeTimer(timestamp);
    -		fireTimestamp.clear();
    +		Long timestamp = fireTimestamp.get();
    +		if (timestamp != null) {
    +			ctx.deleteEventTimeTimer(timestamp);
    +			fireTimestamp.clear();
    +		} else if (cachedFireTimestamp != null){
    +			ctx.deleteEventTimeTimer(cachedFireTimestamp);
    +		}
    --- End diff --
    
    The above `else if` block is not correct because there is only one instance of the trigger which is reused for each Window. Hence the abstraction using the state descriptor to retrieve the appropriate state.


> NPE on EventTimeSessionWindows with ContinuousEventTimeTrigger
> --------------------------------------------------------------
>
>                 Key: FLINK-4862
>                 URL: https://issues.apache.org/jira/browse/FLINK-4862
>             Project: Flink
>          Issue Type: Bug
>          Components: Streaming, Windowing Operators
>    Affects Versions: 1.2.0, 1.1.3
>            Reporter: Manu Zhang
>            Assignee: Manu Zhang
>             Fix For: 1.2.0, 1.1.4
>
>
> h3. what's the error ?
> The following NPE error is thrown when EventTimeSessionWindows with ContinuousEventTimeTrigger is used.
> {code}
> Caused by: java.lang.NullPointerException
> 	at org.apache.flink.streaming.api.windowing.triggers.ContinuousEventTimeTrigger.clear(ContinuousEventTimeTrigger.java:91)
> 	at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$Context.clear(WindowOperator.java:768)
> 	at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:310)
> 	at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:297)
> 	at org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSet.addWindow(MergingWindowSet.java:196)
> 	at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.processElement(WindowOperator.java:297)
> 	at org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:183)
> 	at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:66)
> 	at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:271)
> 	at org.apache.flink.runtime.taskmanager.Task.run(Task.java:609)
> 	at java.lang.Thread.run(Thread.java:745)
> {code}
> h3. how to reproduce ?
> use {{ContinuousEventTimeTrigger}} instead of the default {{EventTimeTrigger}} in [SessionWindowing | https://github.com/apache/flink/blob/master/flink-examples/flink-examples-streaming/src/main/java/org/apache/flink/streaming/examples/windowing/SessionWindowing.java#L84] example. 
> h3. what's the cause ?
> When two session windows are being merged, the states of the two {{ContinuousEventTimeTrigger}} are merged as well and the new namespace is the merged window. Later when the context tries to delete {{Timer}} from the old trigger and looks up the timestamp by the old namespace, null value is returned. 


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