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https://issues.apache.org/jira/browse/HTTPCORE-599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16926601#comment-16926601
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Oleg Kalnichevski commented on HTTPCORE-599:
--------------------------------------------
[~rhashimoto] The cause of the problem turns out the HTTP/1.1 protocol handler
being a bit too greedy when reading data. It would not break the loop in the
`readable ` event as long as it could read some data from the underlying
channel, so cleared interest in read events would never get a change to take
effect. This issue probably only really manifests itself in extreme scenarios
with literally zero latency but it did not get around to verifying that
assumption.
The fix was to moderate the protocol handler greed when interest in read events
got disabled as a result of the actual message exchange running out of
capacity. It however required some changes in the {{IOSession}} API that now
acts as a {{ByteChannel}} and exercises extra control over read / write
operations.
Pull request coming soon.
Oleg
> Capacity feedback does not throttle AsyncDataConsumer.consume() for Http1
> -------------------------------------------------------------------------
>
> Key: HTTPCORE-599
> URL: https://issues.apache.org/jira/browse/HTTPCORE-599
> Project: HttpComponents HttpCore
> Issue Type: Bug
> Components: HttpCore NIO
> Affects Versions: 5.0-beta8
> Environment: macOS Mojave using the IntelliJ CE 2019.2.1 runtime
> Reporter: Roy Hashimoto
> Priority: Major
> Attachments: SlowConsumerTest.java
>
>
> The capacity window mechanism in AbstractHttp1StreamDuplexer does not appear
> to be throttling calls to AsyncDataConsumer.consume(). This affects both
> client and server asynchronous entity consumers.
> The attached test program implements a simple 5.0 asynchronous HTTP/1.1
> server. Aside from boilerplate code, the significant parts are:
> # Set the HTTP1 initial window size to 8192.
> # Add an AsyncExchangeHandler that creates an empty response and logs the
> AsyncDataConsumer method calls to the console.
> # Updating the capacity channel is intentionally omitted, effectively
> providing an infinitely slow consumer.
> To test, post data of more than 8 KB to the server (e.g. using curl). I
> expect to see in the log consume() calls totaling at least 8192 and nothing
> after that until the socket times out. Instead, what I see is consume() calls
> delivering all the data and then streamEnd().
> Here is sample output for uploading almost 32 KB. I have used my IDE to add a
> logging breakpoint to show the capacity window on this line:
> [https://github.com/apache/httpcomponents-core/blob/a60528ea58877d55dab266bd2813e065aac6ff2c/httpcore5/src/main/java/org/apache/hc/core5/http/impl/nio/AbstractHttp1StreamDuplexer.java#L313]
> so those are also included in the output below.
> {{Mon Sep 09, 2019 10:27:18.893 AM SlowConsumerTest main FINE: Listening on
> /0:0:0:0:0:0:0:0:8080}}
> {{Mon Sep 09, 2019 10:27:31.294 AM SlowConsumerTest$MyExchangeHandler
> handleRequest FINEST: handleRequest called}}
> {{Mon Sep 09, 2019 10:27:31.332 AM SlowConsumerTest$MyExchangeHandler
> consume FINEST: consume 8192 total 8192}}
> {{AbstractHttp1StreamDuplexer:313 capacity=0}}
> {{Mon Sep 09, 2019 10:27:31.341 AM SlowConsumerTest$MyExchangeHandler
> updateCapacity FINEST: updateCapacity called}}
> {{Mon Sep 09, 2019 10:27:31.342 AM SlowConsumerTest$MyExchangeHandler
> consume FINEST: consume 8192 total 16384}}
> {{AbstractHttp1StreamDuplexer:313 capacity=-8192}}
> {{Mon Sep 09, 2019 10:27:31.346 AM SlowConsumerTest$MyExchangeHandler
> updateCapacity FINEST: updateCapacity called}}
> {{Mon Sep 09, 2019 10:27:31.348 AM SlowConsumerTest$MyExchangeHandler
> consume FINEST: consume 8192 total 24576}}
> {{AbstractHttp1StreamDuplexer:313 capacity=-16384}}
> {{Mon Sep 09, 2019 10:27:31.352 AM SlowConsumerTest$MyExchangeHandler
> updateCapacity FINEST: updateCapacity called}}
> {{Mon Sep 09, 2019 10:27:31.354 AM SlowConsumerTest$MyExchangeHandler
> consume FINEST: consume 8150 total 32726}}
> {{AbstractHttp1StreamDuplexer:313 capacity=-24534}}
> {{Mon Sep 09, 2019 10:27:31.357 AM SlowConsumerTest$MyExchangeHandler
> streamEnd FINEST: streamEnd called}}
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