RFR: 8357639: DigestEchoClient fails intermittently due to: java.io.IOException: Data received while in pool [v2]

[Daniel Fuchs]

> The java/net/httpclient/DigestEchoClient.java fails intemittently with IOException: HTTP/1.1 header parser received no bytes.
> 
> Analysis shows that this is caused by the CleanupTrigger which receives data after the reused connection has been taken out of the HTTP/1.1 clear pool (Caused by: java.io.IOException: Data received while in pool). This should not happen.
> 
> The fix for [JDK-8338569](https://bugs.openjdk.org/browse/JDK-8338569) has improved the situation but apparently didn't fix the issue completely.
> The issue is that the write publisher manages to come active before the read subscriber has been switched, which opens a window in which the old read subscriber receives the data that should have been passed to the new one.
> 
> To fix that, this change  proposes to pause reading at the selector level before connecting the flows with the new publisher /subscriber pair. This should ensure that data doesn't reach the "old" subscriber, if the new write publisher manage to send data before the new read subscriber is subscribed.

Daniel Fuchs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Access pendingSubscriptions only from InternalReadSubscriptionImpl - and synchronize offer/handle to avoid concurrent removal from the queue
 - Merge branch 'master' into DigestEchoClient-cleanup-8357639
 - Avoid unnecessary volatile reads
 - 8357639

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25416/files
  - new: https://git.openjdk.org/jdk/pull/25416/files/6abcee8f..ad1b28a1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25416&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25416&range=00-01

  Stats: 36183 lines in 726 files changed: 27029 ins; 5883 del; 3271 mod
  Patch: https://git.openjdk.org/jdk/pull/25416.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25416/head:pull/25416

PR: https://git.openjdk.org/jdk/pull/25416