Github user rmetzger commented on the issue:
https://github.com/apache/flink/pull/2080
These are the relevant logs of the task:
```
20:11:35,397 INFO org.apache.flink.runtime.taskmanager.Task
- Attempting to cancel task Source: Custom Source -> Map -> Map (5/8)
20:11:35,398 INFO org.apache.flink.runtime.taskmanager.Task
- Source: Custom Source -> Map -> Map (5/8) switched to CANCELING
20:11:35,398 INFO org.apache.flink.runtime.taskmanager.Task
- Triggering cancellation of task code Source: Custom Source -> Map -> Map
(5/8) (217f8fe570f1c82eb4ec8191e1a73291).
20:12:05,400 WARN org.apache.flink.runtime.taskmanager.Task
- Task 'Source: Custom Source -> Map -> Map (5/8)' did not react to
cancelling signal, but is stuck in method:
org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:235)
org.apache.flink.runtime.taskmanager.Task.run(Task.java:587)
java.lang.Thread.run(Thread.java:745)
20:12:05,510 INFO org.apache.flink.runtime.taskmanager.Task
- Source: Custom Source -> Map -> Map (5/8) switched to CANCELED
```
And this is the code where its waiting:
https://github.com/apache/flink/blob/e7586c3b2d995be164100919d7c04db003a71a90/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java#L235
I don't exactly know why the line numbers don't really match (I would
expect the code to block at the synchronized block) . I've also checked the
lines with the exact commit the error was triggered.
I was not able to reproduce this issue locally. I suspect that somebody is
not releasing the lock...
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