[FLINK-17903] Evolve WatermarkOutputMultiplexer to make it reusable in FLIP-27 Sources

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.11.0
• Component/s: API / DataStream
• Assignee: Stephan Ewen
• Reporter: Stephan Ewen
• Created: 24/May/20 21:17
• Updated: 27/May/20 20:14
• Resolved: 27/May/20 20:14

Description

The WatermarkOutputMultiplexer merges multiple independently generated watermarks.

To make it usable in the FLIP-27 sources, we need to

• Change its IDs from integers to Strings (match splitIDs)
• Support de-registration of local outputs (when splits are finished)