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https://issues.apache.org/jira/browse/FLINK-7416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16212726#comment-16212726
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ASF GitHub Bot commented on FLINK-7416:
---------------------------------------
Github user pnowojski commented on a diff in the pull request:
https://github.com/apache/flink/pull/4533#discussion_r145978661
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/netty/CreditBasedClientHandler.java
---
@@ -269,4 +315,49 @@ private void decodeBufferOrEvent(RemoteInputChannel
inputChannel, NettyMessage.B
bufferOrEvent.releaseBuffer();
}
}
+
+ private void writeAndFlushNextMessageIfPossible(Channel channel) {
+ if (channelError.get() != null || !channel.isWritable()) {
+ return;
+ }
+
+ while (true) {
+ RemoteInputChannel inputChannel =
inputChannelsWithCredit.poll();
+
+ // The input channel may be null because of the write
callbacks that are executed
+ // after each write, and it is also no need to notify
credit for released channel.
+ if (inputChannel == null || inputChannel.isReleased()) {
+ return;
+ }
+
+ AddCredit msg = new AddCredit(
+ inputChannel.getPartitionId(),
+ inputChannel.getAndResetCredit(),
+ inputChannel.getInputChannelId());
+
+ // Write and flush and wait until this is done before
+ // trying to continue with the next input channel.
+ channel.writeAndFlush(msg).addListener(writeListener);
+
+ return;
--- End diff --
So what is the point of having this `while (true)` if it always terminates
after first iteration?
I still think this return is a mistake. Let's say
1. `notifyCreditAvailable` is called 4 times, enqueuing 4 `InputChannel`s
and calling `writeAndFlushNextMessageIfPossible()` 4 times. However because
`channel.isWritable()` returned true, nothing was executed and
`inputChannelsWithCredit` has 4 `inputChannels`
2. channel writability changes, `writeAndFlushNextMessageIfPossible` is
called once, this loop rotates only once, only one `inputChanel` is processed,
`inputChannelsWithCredit` still has 3 elements, which are dangling indefinitely?
> Implement Netty receiver outgoing pipeline for credit-based
> -----------------------------------------------------------
>
> Key: FLINK-7416
> URL: https://issues.apache.org/jira/browse/FLINK-7416
> Project: Flink
> Issue Type: Sub-task
> Components: Network
> Reporter: zhijiang
> Assignee: zhijiang
> Fix For: 1.4.0
>
>
> This is a part of work for credit-based network flow control.
> The related works are :
> * We define a new message called {{AddCredit}} to notify the incremental
> credit during data shuffle.
> * Whenever an {{InputChannel}}’s unannounced credit goes up from zero, the
> channel is enqueued in the pipeline.
> * Whenever the channel becomes writable, it takes the next {{InputChannel}}
> and sends its unannounced credit. The credit is reset to zero after each sent.
> * That way, messages are sent as often as the network has capacity and
> contain as much credit as available for the channel at that point in time.
> Otherwise, it would only add latency to the announcements and not increase
> throughput.
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