rkhachatryan commented on a change in pull request #11507: [FLINK-16587] Add
basic CheckpointBarrierHandler for unaligned checkpoint
URL: https://github.com/apache/flink/pull/11507#discussion_r408111888
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/SingleInputGate.java
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@@ -170,9 +173,14 @@
private final CompletableFuture<Void> closeFuture;
+ @Nullable
+ protected BufferReceivedListener bufferReceivedListener;
Review comment:
Just adding a guard is not enough to protect against visibility issues.
To clarify, I don't agree with @pnowojski:
> I think currently there are no concurrency issues, as this field is being
set very shortly after the construction, before passing it to different threads?
IMO, it doesn't matter whether it is set during construction or not if there
are no memory barriers.
And since `final` is not an option we are only left with `volatile`. Which
as I said we can be cached.
By caching I mean:
1. mark the field `volatile`
1. "constructing thread" writes the value before any following reads
1. "reading thread" uses a non-volatile field which is updated once per
thread in the beginning:
```
if (cachedBufferReceivedListener == null) {
cachedBufferReceivedListener = bufferReceivedListener;
}
cachedBufferReceivedListener.notify(...)
```
I'm not sure whether it's better to place `cachedBufferReceivedListener` in
the input channel or input gate.
(please unresolve this thread)
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