Implement real synchronized processing time in Flink runner #18198
Description
The "continuation trigger" for a processing time trigger is a synchronized processing time trigger. Today, this throws an exception in the FlinkRunner.
The supports the following:
- GBK1
- GBK2
When GBK1 fires due to processing time past the first element in the pane and that element arrives at GBK2, it will wait until all the other upstream keys have also processed and emitted corresponding data.
Sorry for the terseness of explanation - writing quickly so I don't forget.
Imported from Jira BEAM-1641. Original Jira may contain additional context.
Reported by: kenn.