zhijiangW commented on issue #9483: [FLINK-13767][task] Migrate isFinished 
method from AvailabilityListener to AsyncDataInput
URL: https://github.com/apache/flink/pull/9483#issuecomment-525606173
 
 
   My previous thought for this PR is migrating `isFinished` method from 
`AvailabilityListener` to `PollingAsyncDataInput`, and also refactoring the 
`StreamInputProcessor#processInput` to return `InputStatus` instead of boolean 
value as now.
   
   But after thinking through it again, now I find that it would bring 
additional overheads for the implementation of 
`StreamTwoInputSelectableProcessor`.
   
   -  If we do not maintain the `isFinished` flag in `StreamTaskNetworkInput`, 
we have to introduce another two variables for maintaining the first and second 
input status in `StreamTwoInputSelectableProcessor`, because the finished state 
needs to be checked in other processes before calling `emitNext`. 
   
   - Furthermore, only if two inputs are both finished then we can return 
`InputStatus.END_OF_INPUT` to the `StreamTask` while calling `processInput`. So 
we need add additional check process in every call 
`StreamTwoInputSelectableProcessor#processInput`.
   
   Therefore I do not think it is very necessary to do so now. WDYT? @pnowojski 

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