[FLINK-19680] Add EventAnnouncement priority message

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.12.0
• Fix Version/s: 1.12.0
• Component/s: Runtime / Checkpointing
• Labels: pull-request-available
• Assignee: Piotr Nowojski
• Reporter: Piotr Nowojski
• Created: 16/Oct/20 12:51
• Updated: 04/Nov/20 11:07
• Resolved: 29/Oct/20 11:31

Description

When an aligned checkpoint barrier arrives in an input channel, we should enqueue at the head of the queue priority event, announcing arrival of the checkpoint barrier.

Such announcement event should be propagated to the `CheckpointBarrierHandler`. Based on that, `CheckpointBarrierHandler` will be able to implement logic of time outing from aligned checkpoint to unaligned checkpoint.

Issue Links

• links to: GitHub Pull Request #6
• links to: GitHub Pull Request #13741