[FLINK-19223] Simplify Availability Future Model in Base Connector

• Type: Improvement
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 1.12.0
• Component/s: Connectors / Common
• Assignee: Stephan Ewen
• Reporter: Stephan Ewen
• Created: 14/Sep/20 21:13
• Updated: 15/Nov/20 22:09
• Resolved: 15/Sep/20 20:15

Description

The current model implemented by the FutureNotifier and the SourceReaderBase has a shortcoming:

• It does not support availability notifications where the notification comes before the check. IN that case the notification is lost.

• One can see the added complexity created by this model also in the SourceReaderBase#isAvailable() where the returned future needs to be "post-processed" and eagerly completed if the reader is in fact available. This is based on queue size, which makes it hard to have other conditions.

I think we can do something that is both easier and a bit more efficient by following a similar model as the org.apache.flink.runtime.io.AvailabilityProvider.AvailabilityHelper.

Furthermore, I believe we can win more efficiency by integrating this better with the FutureCompletingBlockingQueue.

I suggest to do a similar implementation as the AvailabilityHelper directly in the FutureCompletingBlockingQueue.