loserwang1024 opened a new pull request, #24171:
URL: https://github.com/apache/flink/pull/24171

   ## What is the purpose of the change
   As shown in 
[FLIP-389](https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=278465498),
 this PR has 2 goals:
   
   - To expose the SplitFetcherManager / SingleThreadFetcheManager as Public, 
allowing connector developers to easily create their own threading models in 
the SourceReaderBase.
   
   - To hide the element queue from the connector developers and make 
SplitFetcherManager the only owner class of the queue
   
   
   
   ## Brief change log
   
   - By exposing the SplitFetcherManager / SingleThreadFetcheManager, connector 
developers can easily create their own threading models in the 
SourceReaderBase, by implementing addSplits(), removeSplits() and 
maybeShutdownFinishedFetchers() functions.
   - Note that the SplitFetcher constructor is package private, so users can 
only create SplitFetchers via SplitFetcherManager.createSplitFetcher(). This 
ensures each SplitFetcher is always owned by the SplitFetcherManager.
   
   -  This FLIP essentially embedded the element queue (a 
FutureCompletingBlockingQueue) instance into the SplitFetcherManager. This 
hides the element queue from the connector developers and simplifies the 
SourceReaderBase to consist of only SplitFetcherManager and RecordEmitter as 
major components.
   
   ## Verifying this change
   This change is already covered by existing tests, such as 
HybridSourceReaderTest and SplitFetcherManagerTest.
   
   
   
   ## Does this pull request potentially affect one of the following parts:
   
     - Dependencies (does it add or upgrade a dependency): (no)
     - The public API, i.e., is any changed class annotated with 
`@Public(Evolving)`: (yes)
     - The serializers: ( no )
     - The runtime per-record code paths (performance sensitive): ( no )
     - Anything that affects deployment or recovery: JobManager (and its 
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
     - The S3 file system connector: (no)
   
   ## Documentation
   
     - Does this pull request introduce a new feature? no
     -  how is the feature 
documented?https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=278465498


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