zhijiang created FLINK-8747:

             Summary: The tag of waiting for floating buffers in 
RemoteInputChannel should be updated properly
                 Key: FLINK-8747
                 URL: https://issues.apache.org/jira/browse/FLINK-8747
             Project: Flink
          Issue Type: Sub-task
          Components: Network
    Affects Versions: 1.5.0
            Reporter: zhijiang
            Assignee: zhijiang

In credit-based flow control mode, when the number of available buffers is less 
than required buffers (backlog + initialCredit), the {{RemoteInputChannel}} 
will request floating buffers from {{BufferProvider}}. If not get enough 
available floating buffers, the {{RemoteInputChannel}} registers itself as 
listener in {{BufferProvider}} and updates the tag 
{{isWaitingForFloatingBuffers}} as {{true}} to avoid registration repeatedly.


When a floating buffer is recycled to {{BufferProvider}}, it will notify the 
listener of available buffer. But the listener may not need floating buffers 
currently if the available buffers is not less than required buffers, then the 
floating buffers will be returned to {{BufferProvider}} directly. Most 
importantly, the tag {{isWaitingForFloatingBuffers}} should also be updated as 
{{false,otherwise the }}{{RemoteInputChannel}} will not request floating 
buffers any more after the available buffers less than required buffers.


There are two scenarios for causing the above issue:
 * The recycled exclusive buffers increase the total available buffers which is 
equal to or more than required buffers.
 * The decreased sender's backlog resulting the available buffers equal to 
required buffers.

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