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https://issues.apache.org/jira/browse/BEAM-7520?focusedWorklogId=294928&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-294928
 ]

ASF GitHub Bot logged work on BEAM-7520:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 14/Aug/19 18:46
            Start Date: 14/Aug/19 18:46
    Worklog Time Spent: 10m 
      Work Description: je-ik commented on pull request #9190: [BEAM-7520] Fix 
timer firing order in DirectRunner
URL: https://github.com/apache/beam/pull/9190#discussion_r314028231
 
 

 ##########
 File path: 
runners/direct-java/src/main/java/org/apache/beam/runners/direct/StatefulParDoEvaluatorFactory.java
 ##########
 @@ -244,27 +249,40 @@ public void 
processElement(WindowedValue<KeyedWorkItem<K, KV<K, InputT>>> gbkRes
         delegateEvaluator.processElement(windowedValue);
       }
 
+      Instant lastFired = null;
       for (TimerData timer : gbkResult.getValue().timersIterable()) {
         checkState(
             timer.getNamespace() instanceof WindowNamespace,
             "Expected Timer %s to be in a %s, but got %s",
             timer,
             WindowNamespace.class.getSimpleName(),
             timer.getNamespace().getClass().getName());
-        WindowNamespace<?> windowNamespace = (WindowNamespace) 
timer.getNamespace();
-        BoundedWindow timerWindow = windowNamespace.getWindow();
-        delegateEvaluator.onTimer(timer, timerWindow);
+        checkState(
+            lastFired == null || !lastFired.isAfter(timer.getTimestamp()),
+            "lastFired was %s, current %s",
+            lastFired,
+            timer.getTimestamp());
+        if (lastFired != null && lastFired.isBefore(timer.getTimestamp())) {
+          pushedBackTimers.add(timer);
+        } else {
+          lastFired = timer.getTimestamp();
+          WindowNamespace<?> windowNamespace = (WindowNamespace) 
timer.getNamespace();
+          BoundedWindow timerWindow = windowNamespace.getWindow();
+          delegateEvaluator.onTimer(timer, timerWindow);
 
 Review comment:
   I will add the test and check if there are any issues. Regarding the logic 
you described - generally, yes, that would be the ideal approach. It would also 
solve some other issues, that still remain, even after this PR - but - it would 
require a larger refactoring, because there is currently no simple (or simple 
and apparent to me) way of knowing if `@OnTimer` method actually setup any new 
timer. The `delegateEvaluator` would have to signal that, and that boils down 
to `PushbackSideInputDoFnRunner.onTimer` would have to return the new timers. 
That is API change in core and I wanted to avoid that. But maybe I've 
overlooked  some other way.
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 294928)
    Time Spent: 4h 40m  (was: 4.5h)

> DirectRunner timers are not strictly time ordered
> -------------------------------------------------
>
>                 Key: BEAM-7520
>                 URL: https://issues.apache.org/jira/browse/BEAM-7520
>             Project: Beam
>          Issue Type: Bug
>          Components: runner-direct
>    Affects Versions: 2.13.0
>            Reporter: Jan Lukavský
>            Assignee: Jan Lukavský
>            Priority: Major
>          Time Spent: 4h 40m
>  Remaining Estimate: 0h
>
> Let's suppose we have the following situation:
>  - statful ParDo with two timers - timerA and timerB
>  - timerA is set for window.maxTimestamp() + 1
>  - timerB is set anywhere between <windowStart, windowEnd), let's denote that 
> timerB.timestamp
>  - input watermark moves to BoundedWindow.TIMESTAMP_MAX_VALUE
> Then the order of timers is as follows (correct):
>  - timerB
>  - timerA
> But, if timerB sets another timer (say for timerB.timestamp + 1), then the 
> order of timers will be:
>  - timerB (timerB.timestamp)
>  - timerA (BoundedWindow.TIMESTAMP_MAX_VALUE)
>  - timerB (timerB.timestamp + 1)
> Which is not ordered by timestamp. The reason for this is that when the input 
> watermark update is evaluated, the WatermarkManager,extractFiredTimers() will 
> produce both timerA and timerB. That would be correct, but when timerB sets 
> another timer, that breaks this.



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