zhijiangW opened a new pull request #9905: [FLINK-14396][network] Implement rudimentary non-blocking network output URL: https://github.com/apache/flink/pull/9905 ## What is the purpose of the change Considering the mailbox model and unaligned checkpoints requirements in future, task network output should be non-blocking. In other words, as long as output is available, it should never block for a subsequent/future single record write. In the first version, we only implement the non-blocking output for the most regular case, and do not solve the following cases which still keep the previous behavior. 1. Big record which might span multiple buffers 2. Flatmap-like operators which might emit multiple records in every process 3. Broadcast watermark which might request multiple buffers at a time The solution is providing the `RecordWriter#isAvailable` method and respective `LocalBufferPool#isAvailable` for judging the output beforehand. As long as there is at-least one available buffer in `LocalBufferPool`, the `RecordWriter` is available for network output in most cases. This doesn’t include runtime handling of this non-blocking and availability behavior in `StreamInputProcessor`. Note: It requires the minimum number of buffers in output `LocalBufferPool` adjusting to (numberOfSubpartitions + 1) and also adjusting the monitor of backpressure future. ## Brief change log - Refactor to extract `AbstractAvailabilityProvider` class from `InputGate` logics. - Provide the #isAvailable method for `RecordWriter`, `ResultPartitionWriter` and `BufferPool`. - Refactor the relevant implementations in `LocalBufferPool` for supporting updating the available state. ## Verifying this change Add new `RecordWriterTest#testIsAvailableOrNot` for verifying the changes. ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): (yes / `no`) - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (yes / `no`) - The serializers: (yes / **no** / don't know) - The runtime per-record code paths (performance sensitive): (yes / **no** / don't know) - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / **no** / don't know) - The S3 file system connector: (yes / **no** / don't know) ## Documentation - Does this pull request introduce a new feature? (yes / **no**) - If yes, how is the feature documented? (**not applicable** / docs / JavaDocs / not documented)
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