RFR: 8343855: HTTP/2 ConnectionWindowUpdateSender may miss some unprocessed DataFrames from closed streams [v2]

[Daniel Fuchs]

> [JDK-8342075](https://bugs.openjdk.org/browse/JDK-8342075) has introduced more flow controls checks, but also introduced a race condition where DataFrames for closed streams may fail to be discounted from the connection window.
> 
> The consequence is that WINDOW_UPDATE frames for the connection window may not be sent when they should, preventing the server from making progress and stalling the connection.
> 
> This can be shown by modifying the StreamFlowControlTest to send less but bigger frames (e.g. chunks of 1600 bytes instead of chunks of 12 bytes). With such a modification the test can be seen failing intermittently, when sameClient=true.
> 
> The race happens when frames that have been added to Stream::inputQ fail to be drained after the stream is closed (or continue to be added to the inputQ after the stream is closed).
> 
> The fix ensures that Stream::drainInputQueue() is called when the stream is closed, and that no further data farme will be added to the inputQ after the stream is marked closed.
> 
> The modified StreamFlowControlTest could be observed failing relatively frequently on linux-aarch64 without the fix.
> With the fix the test no longer fails.

Daniel Fuchs has updated the pull request incrementally with one additional commit since the last revision:

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21991/files
  - new: https://git.openjdk.org/jdk/pull/21991/files/318b1811..9d21e58f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21991&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21991&range=00-01

  Stats: 23 lines in 1 file changed: 21 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21991.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21991/head:pull/21991

PR: https://git.openjdk.org/jdk/pull/21991