[FLINK-6464][streaming] Stabilize default window operator names

[zentol]

What is the purpose of the change

This PR modifies the generation of default operator names for window operators to be more concise, and more importantly, stable across job submissions.

Example: SocketTextWordCount

Before:

TriggerWindow(TumblingProcessingTimeWindows(5000), ReducingStateDescriptor{serializer=org.apache.flink.api.java.typeutils.runtime.PojoSerializer@591ae253, reduceFunction=org.apache.flink.streaming.examples.socket.SocketWindowWordCount$1@48974e45}, ProcessingTimeTrigger(), WindowedStream.reduce(WindowedStream.java:241))

After:

Window(TumblingProcessingTimeWindows(5000), ProcessingTimeTrigger, WindowedStream.reduce(WindowedStream.java:243))

Brief change log

• create shared static utility method to generate names
• remove state-descriptor from operator name
• replace TriggerWindow with Window
• trigger/assigner are now included with their simple class name instead of fully qualified class name + object reference

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[aljoscha]

Changes look good!

It might make sense to also remove the line number from the string because this might also change in the future. It's not a must, though.

[zentol]

How about we replace the line-number with the UDF class name?

[aljoscha]

👍

[zentol]

@aljoscha Done, we now include the function name instead. Is a bit more complicated that I had hoped though...

[aljoscha]

Looks good 👍

[zentol]

merging.