Github user NicoK commented on a diff in the pull request:
https://github.com/apache/flink/pull/4552#discussion_r161241148
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/netty/SequenceNumberingViewReader.java
---
@@ -49,10 +50,24 @@
private volatile ResultSubpartitionView subpartitionView;
+ /**
+ * The status indicating whether this reader is already enqueued in the
pipeline for transferring
+ * data or not. It is mainly used for avoid registering this reader to
the pipeline repeatedly.
+ */
+ private boolean isRegisteredAvailable;
+
+ /** The number of available buffers for holding data on the consumer
side. */
+ private int numCreditsAvailable;
--- End diff --
Just a note since I was wondering whether we need synchronization here (not
needed after verifying the things below):
1) `numCreditsAvailable` is increased via
`PartitionRequestServerHandler#channelRead0` which is a separate channel
handler than `PartitionRequestQueue` (see
`NettyProtocol#getServerChannelHandlers`). According to [Netty's thread
model](https://netty.io/wiki/new-and-noteworthy-in-4.0.html#wiki-h2-34), we
should be safe though:
> A user can specify an EventExecutor when he or she adds a handler to a
ChannelPipeline.
> - If specified, the handler methods of the ChannelHandler are always
invoked by the specified EventExecutor.
> - If unspecified, the handler methods are always invoked by the EventLoop
that its associated Channel is registered to.
2) `numCreditsAvailable` is read from
`PartitionRequestQueue#enqueueAvailableReader()` and
`SequenceNumberingViewReader#getNextBuffer()` which are both accessed by the
channel's IO thread only.
---
